Andrea Kelly Lee Freeman
Copyright © Andrea Kelly Lee Freeman 1997
A Dissertation Submitted to the Faculty of the
In Partial Fulfillment of the Requirements
For the Degree of
In the Graduate College
As members of the Final Examination Committee, we certify that we have
read the dissertation prepared byAndrea Kelly Lee Freeman
Middle to Late Holocene Stream Dynamics of the Santa Cruz
River, Tucson, Arizona: Implications for Human Settlement,
the Transition to Agriculture, and Archaeological site
and recommend that it be accepted as fulfilling the dissertation
requirement for the Degree of Doctor of Philosophy
C. V
1D ate
Final approval and acceptance of this dissertation is contingent upon
the candidate's submission of the final copy of the dissertation to the
Graduate College.
I hereby certify that I have read this dissertation prepared under my
direction and recommend that it be accepted as fulfilling the dissertation
Dissertation Director C. Vance Hay es, Jr.
/ 27/
This dissertation has been submitted in partial fulfillment of requirements for
an advanced degree at The University of Arizona and is deposited in the University
Library to be made available to borrowers under rules of the Library.
Brief quotations from this dissertation are allowable without special permission,
provided that accurate acknowledgment of source is made. Requests for permission
for extended quotation from or reproduction of this manuscript in whole or in part
may be granted by the copyright holder.
SIGNED: <!!7,2---'-'
Research for this dissertation was funded by the U. of A. Graduate College, ADoT, the
City of Tucson, the Arizona Archaeological and Historical Society, and the Center for
Desert Archaeology. Radiocarbon assays were provided by Beta Analytic, Inc. and the
University of Colorado Institute for Arctic and Alpine Research.
My sincere gratitude goes to Elizabeth Black and Dena McDuffie for
formatting and editing and to Elizabeth Gray, Rob Ciaccio, and Catherine Gilman for
drafting. Additional mapping and drafting was provided by GEO-MAP, Inc. with
particular recognition to Jim Holmlund for long hours and friendly advice when
needed. Stratigraphic pits were excavated by Paul Giacomino (Desert Diggers) and
Dan Arnit (Innovative Excavating). Josh Edwards, Todd Schmitz, Todd Surovell, and
Vance Haynes' "Late Quaternary Geology" class aided me in geologic mapping.
Many friends and colleagues have stimulated my intellectual development and
supported me with friendship and love. I would like to thank the staff of Desert
Archaeology, Inc. (DAI), the founding members of the Quaternary Alliance (Qal), and
the EGS for their support. Helga Wi5cherl, Chaz Tompkins, Louise Senior, and Dunbar
Birnie allowed me share in the joy of raising their daughters and watching them grow.
The unconditional love and cherished phrases from my friends, April Birnie and
Anwyn Tompkins, rescued me many times with a sense of calm and simplicity that no
one else could muster. Six four-footed friends provided occasional companionship:
Zack, Bones, Amos, Lola, Georgia, and Ripley. Numerous bipeds deserve a special
note of appreciation for devoted encouragement: S. Bierwirth, K. Harry, B. Miksa, K.
Nicoll, M. Slaughter, K. Tankersley, R. VanDyke, L. Young, and T. Young. For those
left out, please know that you are in my heart and mind, but not the regulations of the
Graduate College. Field discussions with E. Hajic, B. Huckell, G. Huckleberry, A.
Meglioli, P. Pearthree, B. Roth, K. Vincent, M. Waters, and colleagues at DAI helped
me to refine my thinking on the relationship between streams and archaeology.
My committee, Vance Haynes, John Olsen, and Steve Kuhn, greatly improved
the content and format of this thesis. All flaws or omissions in this dissertation are
expressly my own. Additional members of my examination committee, David Meltzer,
William Longacre, Vic Baker, and Owen Davis helped me through many difficult and
unpleasant lessons. My advisor, Vance and "ldr," David provided me with the rare
(deserved) scowl and unswerving belief in my abilities. Two other professors provided
appropriate words and inspiration during especially trying times: C. Kramer and M.
Schiffer. My strength to continue in this pursuit came from training and support I
received early in my life. For that unique gift, I thank my former swim coaches and
my parents, Hilda and Ralph Freeman, who taught me to break down walls.
Finally, this research would not have been initiated without the support of my
employer, Bill Doe lle. Bill cajoled me into writing this dissertation and provided the
support for me to do so. I can never thank him enough. If I can ever be worthy of the
faith that those mentioned above have had in me, my life will be fulfilled.
To my grandparents...
David Carlson
Grace Carlson
Marvel Carlson
Samuel Freeman
E. Joan Freeman
...from whom I inherited my life's geography.
Arroyo Cutting and Filling 24
Preceramic Archaeology in the Tucson Basin 31
SOUTHERN ARIZONA INTRODUCTION THE SOUTHWESTERN "ARCHAIC" San Dieguito and Pinto-Gypsum Amargosa The Cochise Culture The Desert Culture PICOSA, Oshara, and the Southwestern Archaic THE MIDDLE ARCHAIC Why So Few Middle Archaic Sites? Characteristics of the Southwestern Middle Archaic Middle Archaic Sites in Southern Arizona Status of the Middle Archaic in Southern Arizona New Hallmarks of the Southern Arizona Middle Archaic Middle Archaic Site Types and Site Distributions THE LATE ARCHAIC/EARLY AGRICULTURAL PERIOD Investigations of Late Archaic/Early Agricultural Sites in
Southern Arizona GEOCLIMATIC MODELS FOR ARCHAIC PERIODIZATION Antevs' Altithermal Correlate Human Responses Altithermal Abandonments? MIDDLE TO LATE ARCHAIC TRANSITION 40
QT5 and QT4 (The Univerisity and Cemetary terraces) 112
Qt3 (the Jaynes terrace) 113
Qt2 (the Holoecene terrace) 113
Qt 1 (the Historic terrace) 115
Unit I 117
Unit II 117
Unit III 118
Unit IV 118
Unit V 118
Unit VI 119
Unit VII 119
Clearwater Site (AZ BB:13:6) 120
Project Area Background 124
Methods 126
Stratigraphy 127
Correlation 138
Summary 140
Stratigraphy 142
Rillito Fan Site (AZ AA:12:788) 147
Methods 148
Results of Geomorphic Study Summary INA ROAD AZ AA:12:111/688 AZ AA:12:130 AZ AA:12:503 Geologic Background Previous Geochronological Work in the Project Area Recent Excavation at AA: 12:503 (ASM) by Statistical Research Recent Excavation at AA:12:130 (ASM) by SWCA Results of Testing Along Ina Road Correlation Summary SILVERBELL ROAD SUMMARY 8
PARK SITES INTRODUCTION Santa Cruz Bend (AZ AA:12:746) Stone Pipe (AZ BB:13:425) Square Hearth (AZ AA:12:745) Juhan Park (AZ AA:12:44) Implications of Excavations at the Santa Cruz Bend, Stone Pipe,
and Square Hearth Sites GEOLOGICAL INVESTIGATIONS Description of the Area The Santa Cruz Bend Profile Sediments Revealed in Juhan Park Archaeological Testing The Juhan Park Profile SUMMARY CHAPTER 6: ALLUVIAL STRATIGRAPHY, GEOCHRONOLOGY, AND
GEOMORPHOLOGY OF THE LOS POZOS SITE INTRODUCTION THE LOS POZOS SITE (AZ AA:12:91, ASM) The Middle Archaic Component The Early Agricultural Period Component METHODS ALLUVIAL STRATIGRAPHY West Side Stratigraphic Trench 173
East-Side Excavation GEOCHRONOLOGY AND CORRELATION Intrasite Geochronology and Correlation Intersite Geochronology and Correlation GEOMORPHOLOGY Environmental Implications of Channel Changes Implications for Human Settlement and Site Preservation SUMMARY CHAPTER 7: THE IMPACT OF MIDDLE HOLOCENE STREAM
Cruz River Short-Term Climatic Changes or Small Scale Threshold Breaches HUMAN SETTLEMENT THE TRANSITION TO AGRICULTURE Models of the Transition to Agriculture New Chronology for Maize The Relationship between Stream Changes
Location of study and focus areas 18
FIGURE 1.2a Location of sites and relevant geologic cross-sections within the study
area 19
FIGURE 1.2b Location of sites and relevant geologic cross-sections with the study
area 20
Distribution of archaeological sites in the study area and their location
on the Holocene (Qt2) terrace 77
Location of Clearwater site showing surficial geologic deposits and
relevant Rio Nuevo and Alameda Street cross-sections, A-A', B-13 1.
C-C 1
FIGURE 4.2 Location of allostratigraphic units identified at the Clearwater site and
relevant trench locations referred to in text 128
FIGURE 4.3 Stratigraphic column south wall of Trench 112 129
FIGURE 4.4 Stratigraphic profile of Trench 12, showing the relationship between
allostratigraphic unit 1 and possible allostratigraphic unit 3 130
FIGURE 4.5 Profile of trenched area showing a north-to-south cross-section of the
alluvial soils (from Elson and Doe lle 1987) 133
FIGURE 4.6 Profile of south wall of Clearwater site stratigraphic pit 135
FIGURE 4.7 Generalized stratigraphic profile of the Clearwater site 137
FIGURE 4.8 Generalized stratigraphic diagram of Alameda Street 143
Surficial geology of the Rillito Fan project area (after McKittrick
1988) showing location of the Rillito Fan site and trenches
described in text
FIGURE 4.10 Historic channel locations along Rillito Creek (after Graf 1984) . 154
FIGURE 4.11 Surficial geology in the Ina Road area (after McKittrick) showing
relevant archaeological sites and geologic cross-sections 163
FIGURE 4.12 Generalized diagram of alluvial stratigraphy along Ina Road (from
Haynes and Huckell 1986) 168
Surficial geology of the Juhan Park and Santa Cruz Bend site areas
showing relevant geologic cross-sections and stratigraphic profiles 174
Generalized stratigraphic columns at the Santa Cruz Bend and Square
Hearth sites, showing inferred correlation of stratigraphic units by
Huckell (1996) 186
Generalized stratigraphic columns at the Santa Cruz Bend and Square
Hearth sites, showing alternate interpretation of correlation between
stratigraphic units 190
FIGURE 5.4 Location of excavated trenches at the Juhan Park site . . . . . . . . . 193
FIGURE 5.6 Stratigraphic column for Juhan Park profile 1 195
FIGURE 5.7 Juhan Park profile 6 196
FIGURE 6.1 Surficial geology of the Los Pozos and Wetlands site areas (after
McKittrick 1988) showing relevant trenches and excavation areas 204
FIGURE 6.2 Map of Wetlands site archaeological excavations 211
FIGURE 6.3 Profile of east side excavation 215
FIGURE 6.4 Profile of west side stratigraphic trench in pocket
FIGURE 6.5 Generalized stratigraphic diagram of the west-side stratigraphic pit at
Los Pozos site 217
FIGURE 7.1 Calibrated radiocarbon age ranges on early maize in the American
Southwest 257
Periodization and chronology of Santa Cruz Valley-Tucson Basin
prehistory (adapted from Mabry 1996) 34
Presence of carbonized maize remains at the Middle Santa Cruz
River sites 78
Correlation between geologic units defined by different researchers 112
AMS radiocarbon dates from A-Mountain mitigation features . . . 123
Stratigraphic descriptions from the south wall of Trench 10,
AZ AA:12:788 150
Stratigraphic descriptions from the north wall of Trench 14,
AZ AA:12:10 151
Radiocarbon dates on alluvial stratigraphic units at the Santa Cruz
Bend and Square Hearth sites (as reported by Huckell 1996) . . . 183
Alternate division of alluvial stratigraphic units at the Santa Cruz
Bend and Square Hearth sites TABLE 6.1
Radiocarbon dates from the Middle Archaic component at Los
Pozos 206
Radiocarbon dates from the Early Agricultural component at Los
Pozos 209
Radiocarbon dates from the Wetlands site 213
TABLE 6.4 Additional radiocarbon dates from the Los Pozos site 218
TABLE 6.5 Estimated age of stratigraphie units at Los Pozos site 233
TABLE 7.1 Earliest radiocarbon dates on cultigens in the Southwest 255
Historic records of arroyo formation have long been used as inferential tools
for reconstructing paleoclimate in the American Southwest. These paleoclimatic
reconstructions have attempted to demonstrate that synchronous incision of river
valleys across the American Southwest was the result of large-scale (regional, global)
climatic change. Projected to the past, the inferred chronological boundaries of certain
climatic periods have been used by archaeologists as convenient boundaries for
demarcating long-term changes in human settlement and subsistence. The rapid
accumulation of new data on middle to late Holocene subsistence and settlement along
the Santa Cruz River, and the application of new theoretical constructs in
hunter-gatherer research require the use of higher resolution data in geoarchaeology.
During the past ten years, advances have been made in our understanding of the
hydroclimatological processes which cause channel changes on the Santa Cruz River
and geologists are now better able to predict the circumstances under which desert
streams become arroyos. Together with high-resolution geologic documentation of
channel exposures, the prehistoric setting of human occupation along the Santa Cruz
River can be addressed at a scale that is more relevant to the archaeological issues of
today. The detail derived addresses specific geomorphic and paleoenvironmental
variables that operate at the site or regional level and that have the most direct effect
on human decision-making.
Though we often think of geologic resources as fixed, they are not. Geologic
resources and features change over time under the force of natural geologic processes.
These geologic processes are initiated by extrinsic and intrinsic forces (or agents),
which include climatic, tectonic, and eustatic forces, biological and chemical agents,
wind, and water. The geologic features created by these processes form the context
for all past and living human groups and influence the lithologic, hydrologic, and
biological resources that are available to these groups.
Of all geologically-formed features, rivers may have the most significant
impact on human decision-making, particularly in prehistory. Rivers provide at least
one critical resource to those groups — water. Rivers form boundaries to human
movement and they provide reliable resources for migratory human groups. They
provide stable, reliable soils on which to grow crops, but they also alter the landscape
on which human groups attempt to live. For archaeologists, rivers provide both the
context for archaeological sites and a force that sometimes removes those sites.
To some extent, geoarchaeology is an opportunistic discipline, because it
exploits the geologic context in which archaeological resources are found' to address
archaeological research issues. Fluvial processes are some of the most active geologic
agents and as a result preserve short-term records of human activity that can span
hundreds or thousands of years. These archaeological records provide chronological
markers by which to measure the activities of rivers and the preserved effects of
fluvial processes. Thus, geoarchaeology can be used as a geoscientific, as well as an
archaeological, research tool. Deposits left by rivers and the archaeological resources
associated with those deposits are interesting to geologists, geoarchaeologists, and
archaeologists, all of whom have had a lengthy relationship with the investigation of
archaeological sites in river settings.
This dissertation explores the relationship between geologic processes and
human occupation of the middle Santa Cruz River, Tucson, Arizona, during the middle
to late Holocene. The geologic period encompassed by this study overlaps the
archaeological periods known as the Middle and Late Archaic. Inferred climatic
changes and the geologic indicators of those changes during the transition from the
middle to late Holocene have been used by archaeologists as convenient boundaries
for demarcating long-term changes in human settlement and subsistence patterns,
including the transition to agriculture. The rapid accumulation of new data used to
address such issues from Middle and Late Archaic sites in southern Arizona and the
application of new theoretical constructs in hunter-gatherer research require the use of
higher resolution data in geoarchaeology.
During the past ten years, advances also have been made in our understanding
of the hydroclimatological processes which cause channel changes on the Santa Cruz
River (Parker 1995). Using data from historic records and recent flooding events in
conjunction with climatic modeling, geologists have been better able to predict the
circumstances under which desert streams become arroyos (Betancourt and Turner
1990; Parker 1995). These data can be used to understand the prehistoric setting of
human occupation in the Tucson Basin at a scale that is more relevant to the
archaeological issues being addressed today. A more complete understanding of
prehistoric stream behavior can also be used to predict the potential for additional, yet
undiscovered, archaeological sites within the prehistoric floodplain of the Santa Cruz
Utilizing prehistoric records of channel change and archaeological evidence for
Middle and Late Archaic sites, this dissertation seeks to evaluate the impact that
current and future discoveries of Middle Archaic sites have on our understanding of
middle to late Holocene prehistory in the Tucson Basin. The dynamic record left by
the Santa Cruz River is used to reconstruct environmental variables important to
understanding prehistoric use of the riverine setting, and to predict the potential for
discovery of additional Middle and Late Archaic sites within the floodplain of the
Santa Cruz River. The dissertation will address the following general issues:
What was the nature of middle to late Holocene floodplain development along
the Santa Cruz River? How are those stream processes related to the
preservation of middle to late Holocene archaeological sites?
What was the nature of human settlement and subsistence along the Santa Cruz
during the middle to late Holocene? How did channel change during this
period influence human decisions regarding settlement and subsistence?
Was the Santa Cruz floodplain environment during the middle Holocene
conducive to the introduction of cultigens and is there support for the presence
of cultigens during this period?
In order to address the above general issues, the middle Santa Cruz River
surrounding Tucson, Arizona, has been subdivided into two areas: the study area and
the focus area (Figure 1.1). The study area refers to the stretch of the Santa Cruz
River from A-Mountain (Sentinel Peak) to Ina Road. The study area represents the
portion of the Santa Cruz that has been investigated by the author. This area has been
sampled (i.e., prehistoric alluvium has been documented) rather thinly, providing
low-resolution data for portions of the study area. With the exception of the
Clearwater site, archaeological sites within the study area but outside the focus area
have also been thinly sampled (i.e., tested rather than mitigated). The results of this
geologic and archaeological sampling effort are presented in Chapter 4. Sites and
relevant geologic sections are presented in Figure 1.2. A portion of the Santa Cruz
outside the study area from Pima Mine Road to A-Mountain has been investigated
previously by other authors (Haynes and Huckell 1986; Stafford 1986; Waters 1987,
1988) and the results of their work are also reviewed in Chapter 4.
Figure 1.1. Location of study and focus areas.
(i" ow.......
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contours ..."'"•• river bank profile
1 AZ AA:12:745 — square hearth
stratigraphic pit
2 AZ AA:12:746 — Santa Cruz Bend
contour interval — 100 feet
contour interval below 2400 feet — 20 feet
3 AZ AA: 12:746 — Santa Cruz Bend,
river bank profile
4 AZ AA:12:44 — Juhon Park profile 6
5 AZ AA:12: 44 — Juhan Park profile 1
B AZ BB:13:16 — Clearwoter site
1 .0
2.0 km
1.0 mi
Digital cartography by CEO—MAP, Inc. 1997
Figure 1.2a. Location of sites and relevant geologic cross-sections within the study area.
AZ AA:12:130
2 AZ AA:12: 503
3 AZ AA:12:111/688
4 AZ AA:12:10 — Trench 14 Sunset Mesa
contour interval — 100 feet
contour interval below 2400 feet — 20 feet
5 AZ AA:12:788 — Trench 10 KR() Fan
6 AZ AA:12: 91 — west side stratigraphic pit
2.0 km
7 AZ AA:12: 91 — Los Pozos excavations
8 AZ AA: 12:91 — Los Pozos east side excavations
9 AZ AA:12:90 — Wetlands site
.1.0 mi
Digital cartography by CEO—MAP, Inc. 1997
Figure 1.2b. Location of sites and relevant geologic cross-sections within the study area.
The focus area, which is inset within the study area, refers to the stretch of the
Santa Cruz River from Grant Road to Ruthrauff Road. The focus area has been
intensively documented, geologically and archaeologically (through site mitigation),
providing high-resolution data for a specific portion of the river. The results of
research within the focus area are presented in Chapters 5 and 6.
Although both the study area and the focus area have been selected, in part, on
the basis of the needs of cultural resource management, the areas are quite appropriate
for the issues presented in this study. In an attempt to provide a geomorphic and
hydrologic explanation for channel change on the Santa Cruz, Parker (1995) has
identified certain landforms within the middle Santa Cruz that provide geologic and
topographic controls on channel changes. His study reaches are defined on the basis
of those landforms. The three reaches that he defines within the Tucson Basin are
either partly or fully covered by the research in the study reach and by the efforts of
previous investigators (Haynes and Huckell 1986; Stafford 1986; Waters 1987, 1988)
outside the study reach. The focus reach samples a limited portion of what Parker
(1995) has identified as the Tucson reach of the middle Santa Cruz. A discussion of
Parker's (1995) defined reaches is provided in Chapter 3, along with a discussion of
the data used to infer the prehistoric character of the Santa Cruz from documented
prehistoric alluvium.
Research within the study and focus areas provides two different scales of data
from which to interpret the relationship between stream processes and prehistoric
human decision-making. General trends can be inferred from low-resolution data
within and outside the study reach, while specific, higher frequency processes are
documented within the focus reach. The scale at which archaeologists and geologists
study the past is related to progress made in data acquisition and data interpretation
(Stein 1993). During the past ten years, both geologic and archaeological research
have made considerable progress, allowing geoarchaeological research to better address
issues in both sciences at an appropriate scale.
The remainder of this chapter briefly charts the history of progress made in the
interpretation of alluvial stratigraphy, the relationship between fluvial processes and
climatic change, and the acquisition of additional data on the Middle and Late Archaic
periods in southern Arizona. Additional background information related to the Middle
to Late Archaic transition in southern Arizona is addressed in Chapter 2. Chapter 3
covers new data on the relationship between channel changes and hydroclimatological
processes on the Santa Cruz River.
The investigation of archaeological sites in the American Southwest has
established a long and close relationship with the geosciences. The two most
influential persons in the early study of Southwestern geoarchaeology were Ernst
Antevs and Kirk Bryan. Both scientists were interested in the relationships between
climatic change and geologic processes and utilized archaeological resources as a
means of measuring these changes. Both scientists also found a place for this research
in the American Southwest. Kirk Bryan's influence on Quaternary geology and
archaeology in the Southwest was passed on from generation to generation by his
students (Haynes 1990), while Antevs began a lifelong collaboration with Ted Sayles
that would define the Cochise culture (Haynes 1990) and set preceramic
geoarchaeology in southern Arizona on its current path.
As time passed, more geologists became interested in the records left by fluvial
systems. During the 1960s, Quaternary scientists, many of them Bryan's students
(Haynes 1990), struggled to understand the processes that cause changes in river
valleys. Detailed observations of these processes in field and laboratory settings
enabled them to better understand the mechanics of fluvial geomorphology (Leopold et
al. 1964).
Interest in field documentation of processes subsided with the development of
computers and their use in simulation modeling. The application of
computer-generated models to the geoscientific study of hazard reduction led scientists
interested in fluvial geomorphology away from studies of the causes of catastrophic
events in river systems to mathematically-based management and prediction of future
flood events (Baker 1988a, b). Questions of scale became even more important when
geologists realized that predictive modeling based on the historical record was poor at
predicting global changes in fluvial systems (Baker and Twidale 1991). Research in
planetary geomorphology, a product of the 1980s and 1990s, has attempted to address
issues of scale. In response to concerns about the nature of global climatic changes
and unusually high frequency of extreme flooding events, geologists have attempted to
extend their predictive models back into the past, a process that involves the field
application of new knowledge. The one issue that pervades attempts to extend
predictive models into the past has come full-circle back to the research of Antevs and
Bryan — the cause of arroyo cutting and filling.
Arroyo Cutting and Filling
One of the predominant themes throughout Bryan's and Antevs' research was
the cause of arroyo cutting and filling and the relationship of these events to climatic
change (Antevs 1936, 1952; Bryan 1925, 1927, 1928, 1940). Interest in these
processes was a result of the fact that most large river valleys across the Southwest
became entrenched during the period 1865-1915. The relative synchroneity of this
event across the region caused scientists to speculate about the cause of arroyo cutting.
Discussion of the "arroyo problem" was highly charged and the interests of those
involved were usually intertwined with their conclusions (Cooke and Reeves 1976;
Haynes 1968, 1990).
...there is a certain correlation between the professional interests of
investigators and the conclusions they reach on the causes of arroyo
cutting. Agriculturalists, foresters, and conservationists commonly
indict man for his excesses. In contrast, some geologists,
paleontologists, and archaeologists have sought and found "natural"
explanations (Cooke and Reeves 1976:6).
Because the events preceding historic entrenchment included a variety of human and
natural agencies, the causes of this event were the subject of intense debate. A
comprehensive discussion of this debate is found in Cooke and Reeves (1976).
Recognizing this implicit warning against ignoring other causes 2, the following
overview of the literature briefly touches on the arroyo cutting and filling debate and
covers only the parameters encompassed by geomorphic, hydrologic, and climatic
processes. Arroyo cutting and filling has been the focus of studies of prehistoric
alluvium and is critical to understanding the history of research preceding this study.
Over the past 75 years, significant progress has been made in understanding the
geomorphic and hydrologic processes involved in arroyo cutting and filling and the
significance of these events. Because much of this literature has been covered in
previous reviews (Betancourt 1990; Betancourt and Turner 1990; Cooke and Reeves
1976; Graf 1983; Webb 1985), only a cursory examination is presented here.
Climatic Changes and Arroyo Incision
During the early part of this century, most geologists agreed that arroyo cutting
was a synchronous event across the American Southwest, and geologists studying past
arroyo cutting events believed that entrenchment was caused predominantly by
climatic change'. The question boiled down to whether the climatic change that
caused arroyo cutting represented a shift to a wet or a dry period.
Original arguments supporting the wet-period incision hypothesis were drawn
out of the flawed concept that stream gradient was a function of "balance between
erosion and deposition" of sediments (Davis 1902:86). Huntington (1914) applied this
concept to arroyo forming processes by arguing that aridity would increase gradients
causing transportation of sediments and aggradation, while humidity would decrease
the gradient of a stream resulting in entrenchment. He contended further that the loss
of vegetative cover during dry periods would overload streams with alluvium, while
improved vegetative cover would reduce sediment loads, causing clearer, more erosive
flows. Huntington's concept would soon take a subordinate position to Bryan's
dry-period incision hypothesis.
In his study of the Rio Puerco, Bryan (1928) advanced the argument that dry
periods would be accompanied by a reduction of vegetative cover resulting in
increased and more powerful runoff which would initiate gullying in critical reaches.
Bryan's concept derived from an understanding that stream gradients were not
necessarily in equilibrium. He further contended that discontinuous arroyos were
integrated by headward migration of cutting during subsequent floods, forming
continuously entrenched arroyos.
Bryan's concepts were soon adopted by other alluvial stratigraphers (Antevs
1952; Euler et al. 1979; Hack 1939; Haynes 1968; Leopold and Miller 1954) to
support the idea that two periods of synchronous arroyo cutting in Holocene prehistory
represented dry periods (the Altithermal and the "Great Drought"). The application of
radiometric dating to alluvial sequences supported the timing of these arroyo cutting
events (Haynes 1968). Some of these studies of prehistoric alluvium have suggested
that lowered groundwater during drought periods would increase the erodability of
unconsolidated sediments near streams (Euler et al. 1979; Haynes 1968).
But understanding the relationship between climate and erodability of
sediments was still considered much more complex. In addition to the difficulty in
identifying specific cause-and-effect relationships, the scale and complexity of
relationships between precipitation, temperature, soils, water table, plant growth, and
other biological activity was still poorly understood. The simple dichotomy created by
earlier studies was considered too restrictive. The concept that united earlier studies
(synchroneity) would be put to the test in future research.
Synchroneity vs. Asynchroneity
The apparent synchroneity of arroyo incision across the Southwest during the
historic period allowed scientists to utilize the concept of synchronous incision to
reconstruct past river behavior. It is important to note the scale at which
climatological changes were supposed to have driven changes in hydrologic processes.
Most of the studies cited above, and a later study relating Holocene ice advances to
valley degradation (Brackenridge 1980), deal with processes occurring on the order of
several millennia. That synchronous incision caused by climatic changes has occurred
during certain periods is undeniable (Knox 1995); however, not all channel cutting
events are caused by climatic changes. Evaluation of both the scale and timing of
these events is critically important to interpreting whether or not they are synchronous.
In his well-documented case for synchroneity, Haynes (1968) demonstrated that the
periods of entrenchment were short compared to the periods of aggradation. The
synchroneity of cutting events is also more difficult to evaluate than the synchroneity
of filling events. This is partly due to conditions of preservation and the presence of
material evidence for the timing of cutting events. Soil formation can continue for
long periods on an unincised surface. Further, Haynes (1968:613) suggests that the
perturbations caused by climatic changes resulted only in trends favoring one process
over another:
This is not to say that either erosion or deposition began everywhere at
the same time. It does suggest, however, that there were periods when,
throughout the Southwest, processes of aggradation were dominant and
other periods when degradation predominated.
However, probabilistic treatments of flood hydrologic processes argue against
synchronous arroyo development (Hirschboeck 1987; Knox 1983). When combined
with the errors inherent in radiometric dating of these events', the localization of storm
events, and the effect of response time of the fluvial system to climatic perturbations
(Brackenridge 1981), the concept that synchronous processes, caused by a single
climatic anomaly, could encompass an entire region becomes less compelling.
Another study has demonstrated that the number, character, and chronological position
of degradation and aggradation phases over the past 15,000 years are out of sequence
across several valleys in southern Arizona (Waters 1985; Waters and Kuehn 1996).
Rainfall, Climatic Change, and Prehistoric Incision
In order to address the relationship between climatic change and arroyo
incision, several scientists conducted studies specifically geared to determine the
effects of rainfall on arroyo development (Leopold 1951; Leopold et al. 1966; Leopold
and Miller 1954; Thorthwaite et al. 1942). The intensity of rainfall appears to be a
critical factor in arroyo development. Leopold and Miller (1954) determined that
monsoonal moisture is the source of most heavy rainfall in the American Southwest.
Martin (1963) used this concept in his interpretation of palynological data from the
Southwest in order to argue that increases in summer rainfall caused arroyo incision.
His work was subsequently scrutinized and overturned (Antevs 1962; Mehringer
1967). Many of these studies probably focused too heavily on vegetation, but the
lasting conclusion was that rainfall intensity caused large floods and entrainment as
well as entrenchment of river sediments.
Floods and Hydrology
Betancourt and Turner (1990) provide convincing evidence that regardless of
the hydrologic and geomorphic constraints posed by human and natural activity,
entrenchment in large valleys across Arizona could not have occurred without
significant flood flows. These flood flows are attributed to three types of storms:
frontal systems, which occur in the winter; dissipating tropical cyclones, which tend to
occur in early fall; and intense, localized convective storms, which occur during the
summer "monsoon" season (Hirschboeck 1985; Webb and Betancourt 1992). The
entrenchment of historic arroyos throughout the American Southwest seems to have
been caused by extraordinary flood events (Betancourt and Turner 1990; Gregory
1917; Hereford 1985; Huntington 1914; Love 1983; Thornthwaite et al. 1942; Tuan
1966; Webb 1985). These floods succeed in entraining channel materials because
discharges exceed the threshold for erosion (Bull 1979), causing channel entrenchment.
Relationships between large floods and atmospheric circulation patterns are
well documented (Hirschboeck 1985, 1987; Maddox et al. 1980). Although flooding
events in the Southwest do cluster temporally (Ely 1992), large-scale atmospheric
circulation patterns cause spatial-clustering in large flood events (Hirschboeck 1987;
Knox 1983), arguing against their synchroneity. Though the time-spans in which these
major floods are clustered are short, they have a significant impact on the character of
desert streams and tend to cross the threshold conditions that cause perturbations in
stream systems (Baker 1988; Bull 1988; Kochel 1988; Kochel et al. 1982). Parker
(1995) has further elucidated this relationship, demonstrating that monsoonal moisture
due to its flashy, but spatially restricted precipitation pattern does not produce
discharges large enough to sustain energy through the stream system, while tropical
and frontal storms are able to sustain such energy due to their widespread distribution
and sustained periods of moisture.
Despite the well-documented relationship between large-scale atmospheric
circulation patterns and the response of fluvial systems today, the prehistoric
relationship between atmospheric circulation and channel change is poorly studied.
Global climatic modeling cannot accurately predict the intricacies of time-clustered
flood events. So, how can prehistoric alluvial records be used to determine the effects
of climatic change on stream systems?
Modeling the Relationship between Hydroclimatic Processes and Channel Change
Recently, Parker (1995) has attempted to utilize the physical characteristics of
the river, the relationship between meteorological events and streamflow, and historic
records of meteorological events, flooding, and channel change to develop a predictive
model for channel changes along the Santa Cruz River. He also attempts to explain
Holocene alluvial history, documented near San Xavier and Ina Road, by extending
this model into the past. The controls that Parker (1995) describes and the model he
creates are addressed in greater detail in Chapter 3. He uses high-resolution events to
develop this predictive model, but is unable to test the model because of the relatively
low resolution of the Holocene stratigraphic record.
Recent archaeological research in the Tucson Basin has exposed additional
sections of the Holocene alluvial record allowing for higher-resolution testing of
Parker's (1995) model. The transitions in human settlement and subsistence covered
by this archaeological record can also be used to determine whether the results of
modeling channel change can be used to address the scale of archaeological research
questions being posed by middle to late Holocene archaeology.
Preceramic Archaeology in the Tucson Basin
Ten years ago the preceramic (Archaic) period in the Tucson Basin was poorly
known and even more poorly understood. Several large surveys (Doelle 1985; Fish et
al. 1985; Huckell 1984a; Simpson and Wells 1983; Tagg and Huckell 1984) had
produced numerous preceramic sites in the upper bajada and surrounding piedmont. A
few Archaic sites were known to exist in the basin itself (Betancourt 1978; Haynes
and Huckell 1986), but fewer yet were excavated (Elson and Doelle 1987). Even less
well known was the extent of Archaic archaeological resources buried under the
floodplain of the Santa Cruz River. Indication that archaeological sites of preceramic
age existed below the floodplain consisted of occasional clusters of artifacts,
fire-cracked rock, human bone, or the rare hearth, discovered in the most unfortunate
of circumstances — fortuitous exposure, in landfill pits, by construction equipment, or
exposure after large-scale flooding events (Betancourt 1978; Haynes and Huckell
During the past six years, numerous new discoveries of preceramic remains
have been made along the Santa Cruz River as part of projects to improve the
interstate and other parcels of land near the river (Diehl 1996a, 1996b; Ezzo and
Deaver 1996; Freeman 1995, 1996, 1997; Gregory 1995, 1997a, 1997b; Huckell 1990,
1995; Huckell et al. 1994; Mabry 1995, 1996a; Mabry and Clark 1994). Contract
archaeologists have discovered large Late Archaic (also referred to as Early
Agricultural Period') settlements along the Santa Cruz River dating between 3500 and
2000 B.P. These earliest farmers utilized a river that was far more reliable than the
dry arroyo that exists today.
In addition to the late preceramic evidence recovered from floodplain sites, the
past two years have witnessed additional evidence for an earlier (Middle Archaic)
occupation along the Santa Cruz River (Gregory 1995, 1997a). Though hints of this
earlier occupation have been recovered through fortuitous discoveries and geologic
investigations of the exposed banks of today's dry arroyo (Haynes and Huckell 1986;
Huckell 1996a), recent excavation of a Middle Archaic component suggests that a
Middle Holocene occupation of the Santa Cruz River did exist and may have been the
precursor to an Early Agricultural period occupation of the river valley. In light of
this new evidence, it has become necessary to re-evaluate the nature of the Middle to
Late Archaic period transition in the Tucson Basin.
Archaic Periodization
Discoveries of these early farming villages have caused archaeologists to
re-evaluate the current cultural-historical scheme and to propose a new sequence for
the Archaic period in southern Arizona (Table 1.1). Under this scheme, the Early
Archaic period, which is poorly known from in southern Arizona, encompasses the
period of time from 10,500 to 8000 B.P. (Mabry 1996a; but see, Haynes 1967:278;
Huckell 1984:137; Huckell 1996b; Huckell and Haynes 1995; Martin 1963:57; Waters
1986b), equivalent to Sayles and Antevs, (1941) Sulphur Spring stage of the Cochise
culture. The Early Archaic is defined predominantly on radiocarbon dates and artifacts
recovered from Ventana Cave and Whitewater Draw, and is characterized by simple
ground stone milling equipment and flaked stone implements. Early studies placed
these milling tools in association with late Pleistocene megafauna (Sayles and Antevs
1941; Haury 1960); however, further study of the stratigraphy at Double Adobe
suggests that the two occupations are not contemporaneous (Waters 1986a).
Nevertheless, it appears that shortly after the extinction of late Pleistocene megafauna,
on which Paleoindians at least partly relied, groups in southern Arizona established an
economy that demonstrates a certain reliance on plant processing.
A gap (8000-5000 B.P.) is represented by a period in which archaeological
Table 1.1
Periodization and chronology of Santa Cruz Valley-Tucson Basin prehistory (adapted
from Mabry 1996a).
Date Ranges
Hohokam Classic Period
Hohokam Sedentary Period
Hohokam Colonial Period
Tucson phase
A.D. 1300--1450?
Tanque Verde phase
A.D. 1150--1300
Late Rincon phase
A.D. 1100--1150
Middle Rincon phase
A.D. 100--1100
Early Rincon phase
A.D. 950--1000
Rillito phase
A.D. 850--950
Canada del Oro phase
A.D. 750--850
Hohokam Pioneer Period
Early Ceramic Period
Late Archaic/
Early Agricultural Period
Archaic Period
Snaketown phase
A.D. 700--750
Sweetwater phase
A.D. 675--700
Estrella phase
A.D. 650--675
Tortolita phase
A.D. 550--650
Agua Caliente phase
A.D. 150--550
Cienega phase
800 B.C.--A.D. 150
San Pedro phase
1200--800 B.C.
Chiricahua phase
3000--1200 B.C.
Unnamed phase (gap?)
6000--3000 B.C.
Sulphur Springs-Ventana
8500--6000 B.C.
Paleoindian Period
materials are not found (Berry and Berry 1986; Huckell 1996b; Irwin-Williams and
Haynes 1970), possibly due to loss of older sediments in river valleys (Waters 1986b).
Preliminary analysis of data from archaeological site records indicates that the gap in
human occupation is real (Mabry et al. 1997). The climatic, chronological, and
archaeological implications of this apparent gap are explored further in this
The Middle Archaic period begins approximately 5000 B.P. and continues to
3500 B.P. (Mabry 1996a; but see Huckell 1996b), at which time the initial transition
to agriculture is thought to have taken place. Middle Archaic groups, discussed
further in Chapter 2, are denoted by the presence of diagnostic projectile points and
ground stone tools that appear to be, on the whole, slightly more sophisticated than
Early Archaic ground stone implements. Much of the ground stone found at Middle
Archaic sites is more heavily worn, suggesting a reduction in mobility and/or perhaps
a frequent return to resource areas. The implications of mobility changes are explored
further in Chapter 2.
From 3500 to 2000 B.P. (Mabry 1996a), large-scale agricultural occupations
are believed to have begun in the American Southwest. This period has been called
the Early Agricultural period (Huckell 1995) and is thought to include groups both
possessing the ability and incentive to produce domesticated plants (Early Agricultural
period groups) and those that remain committed to a hunting and gathering lifestyle
(Late Archaic period groups). Soon after early farming villages appear, pottery
production begins. The Early Ceramic period (2000 to 1500 B.P.) is defined by the
presence of untempered, plain ware pottery and figurines (Mabry 1995).
Middle to Late Holocene Sites within the Study Area
This dissertation focuses predominantly on the middle to late Holocene or
Middle and Late Archaic periods in the Tucson Basin. Evidence for a Late Archaic
occupation of the floodplain is abundant, but Middle Archaic sites are found in only a
few locations. A possible Middle Archaic component was recorded along Ina Road
(Haynes and Huckell 1986) and two others were recorded near Martinez Hill (Haynes
and Huckell 1986; Huckell 1996b:338, unpublished field notes, pers. comm. 1997).
The excavation of the Los Pozos site (Gregory 1997a) provides a third Middle Archaic
locality and suggests that a fourth, at the Cortaro Fan site (Roth 1989), may yet exist 6.
As this evidence has mounted, our knowledge of the transition between the Middle
and Late Archaic periods has changed significantly.
The Middle to Late Archaic Transition
Though projectile points dating to the Middle Archaic period are found
throughout the Tucson Basin, and hearths and occupation horizons radiocarbon dated
to this period have been found buried in floodplain sediments (Haynes and Huckell
1986; Huckell 1996b), relatively little is known about this period. The "transitional"
period (ca. 3500-2800 B.P.) is poorly represented in the Santa Cruz floodplain, but is
known from other drainages in southern Arizona (Huckell 1990, 1995). Within some
of the Middle Archaic and "transitional" features found in the Santa Cruz floodplain is
sporadic evidence of cultigens (represented by fragmentary corn cupules). Further
investigation of the origin and context of the deposits is necessary in order to
accurately assess the importance of these finds.
The period following this initial occupation or reoccupation of the river valley
is thought to have supported the first agriculturally-based economies in the Tucson
Basin. Huckell (1990) has recently suggested that agriculture may have spread from
Mexico to the American Southwest along northward trending river valleys. He
supports this, in part, from the alluvial record, demonstrating that in the period
following 4500-4000 B.P., river valleys in southern Arizona experienced a trend
toward net aggradation. Yet, without excavation of these buried Middle Archaic
components, it is difficult to determine when and how quickly the shift to an
agricultural economy took place.
Middle Archaic sites along the Santa Cruz River are situated along the margins
of the Pleistocene terrace, in an area that is particularly conducive to the recovery of
subsurface data in stratified sites because of its presence away from the active channel,
an issue explored in more detail in Chapter 7. Furthermore, the large number of
well-documented archaeological sites in southeastern Arizona provide a robust record
of the archaeology bracketing the poorly understood Middle Archaic period. Recent
study of a buried Middle Archaic component along the Santa Cruz River (Gregory
1997a) has enhanced a rather mundane picture of the Middle Archaic occupation of
the Tucson Basin.
The Holocene alluvial record in southeastern Arizona has not only preserved
the record for middle to late Holocene archaeological sites, but has provided additional
data on the varieties of human activities in different physical settings. This, combined
with palynological and faunal data available from excavated archaeological and
geologic sites, increases the database necessary to reconstruct human activity during
this period.
At the same time, archaeological sites can also be used as a tool to understand
the nature of arid region stream activity, its relationship to climatic variability, and the
degree of synchroneity of Holocene stream processes. A portion of the dissertation
will address issues critical to understanding the nature of desert stream processes, their
relationship to archaeological deposits and human occupation, and will evaluate
geologic models of Holocene alluvial activity. A summary of these issues is presented
in Chapter 7.
1. Other types of geoarchaeological study can also be opportunistic. For example,
petrography exploits the geologic resources found in artifacts or from which artifacts
are made in order to address archaeological issues.
2. Prehistoric cutting and filling is very likely not a product of human intervention;
however, seismic events may have played a role.
3. Antevs (1936) believed that historic arroyo cutting was caused by human
intervention, but that past episodes of arroyo cutting were climatically induced.
4. Haynes (1968) has developed a method of reducing errors in dating alluvial events;
these include sampling from the base of each paleochannel as well as the top of each
unit "where it is least eroded" (Haynes 1968:596). He also emphasizes paying close
attention to the possibility of redeposition and/or sample contamination.
5. Huckell's (1995) primary reason for defining the Early Agricultural period is to
acknowledge the quite obvious and well-defined transition to agriculture during the
Late Archaic. The term, therefore, reflects an "adaptive" significance rather than a
temporal one.
6. The presence of Cortaro points at Los Pozos in Middle Archaic contexts raises the
question of whether those same types of points found earlier at the Cortaro Fan site
were Late Archaic, as dates from the site suggest, or Middle Archaic, as dates from
Los Pozos suggest. Roth and Huckell (1992) have chosen to view them as both
Middle and Late Archaic in age.
The term "Archaic" was first used to describe groups in eastern North America
(and later in California) with a specific suite of material culture traits. These traits
included the presence of shell mounds, "crude" stemmed projectile points (Haag 1942),
and in some cases, early pottery (Beardsley 1948). The economic implications
associated with these material culture traits included some combination of hunting and
collecting (Fairbanks 1942) or hunting-gathering-fishing (Beardsley 1948, Haag 1942).
By 1946, increasing desire to relate these groups to their post-Paleoindian and
pre-Agricultural counterparts throughout North America led Griffin (1946) to forward
a cultural-developmental framework. This framework related groups in the United
States to late Paleolithic and early Neolithic groups in Europe, using the terms
"Paleo-Indian" and "Neo-Indian," respectively.
Willey and Phillips (1958:07) were perhaps the first to attach an explicitly
adaptive definition of the Archaic, defining it as "...the stage of migratory hunting and
gathering cultures continuing into environmental conditions approximating those of the
present." Though they note that the Archaic postdates the extinction of late
Pleistocene megafauna, their definition is too broad to be applicable today, for it
would encompass (rightly or wrongly) the late Paleoindian period on the High Plains
and all historic hunters and gatherers. Although the concept of an Archaic period is
basically understood by most North American archaeologists, the definition of it is
never quite specific enough to separate it from the preceding Paleoindian period or
from contemporaneous groups with different economic and social practices. The
problem faced by Willey and Phillips (1958) and by other archaeologists (Caldwell
1965; Cleland 1976; Stoltman and Barreis 1983) who have attempted to segregate the
"Archaic" from the preceding "Paleoindian" and numerous antecedant periods—
variously defined in terms of increasing sedentism, and the adoption of agriculture and
ceramic technology—is that no fixed criteria adequately describe the range of behaviors
encompassed during the post-Pleistocene period.
In order to segregate the Archaic from the Paleoindian period, Willey and
Phillips (1958) defined the Archaic period as existing within an environment that was
essentially the same as that of the present. Although the period encompassed by the
Archaic (the Holocene) is in geologic terms essentially a "modern" climate, it actually
represents a series of conditions, most of which were climatically very distinct from
the present (COHMAP Members 1988). Though many significant changes in human
activity appear to broadly follow long-term climatic changes, there may actually be
some lag time (or response time) which allows significant changes in human behavior
to be noticeable after long-term climatic changes are well established.
The definition provided by Willey and Phillips also supplies no termination
point aside from the general concept of "hunting and gathering cultures." The
termination is essentially the successful integration of agriculture and well-established
(sedentary) village life. This very broadly defined concept was acceptable in an era
when archaeologists relied heavily on cultural-historical frameworks. However, since
the late 1950s, American archaeology has undergone a number of significant
theoretical changes in the way that changes in human groups are viewed. Prehistoric
changes in human economy, mobility, and subsistence-related behavior are viewed
very differently by archaeologists in competing theoretical schools (Kelly 1995).
Though today many archaeologists still use the broad and inclusive term "adaptation,"
implying directional evolutionary change in human behavior, most agree that
understanding the complexity of those changes requires sophisticated analytical
techniques based on a thorough understanding of the environmental and cultural
variables about which individuals made choices.
Because Archaic archaeologists in the American Southwest have so little data
to work with, they are often able to skirt issues of theoretical construct, basing
inferences regarding changes in human settlement and subsistence on a database that
encompasses a geographically or temporally broad scale and that is comprised of many
small fragments of data. As a result, their conclusions are the direct result of where in
space or time they have selected to lump each of these small fragments, rather than on
changes that are significant at the human scale. The result is a competition between
paradigms (often north vs. south) that creates little cohesion in the study of the
"Archaic." For instance, working on the Colorado Plateau, Matson (1991) and Geib
(1995) would place the Middle Archaic between 6000 and 4000 B.P., while Huckell
(1996b), working in southern Arizona, would place it between 5500 and 3500 B.P.
Without working from the same set of inferential rules (or at the very least, obvious,
but different sets of inferential rules), archaeologists working in these two areas have
difficulty communicating the results of their analyses.
As a result of historical precedent, definitions of the "Archaic" are often
"adaptive, evolutionary, [unidirectional], and temporal" (Huckell 1993). The single
criterion which most readily segregates the Archaic from the Paleoindian and
Formative (or Early Agricultural) periods is the integration of tools specifically
manufactured for more intensive preparation of wild plant foods. This does not mean,
as some have implied, that the preceding groups "specialized" in big-game hunting or
that wild food processing was abandoned when plants were cultivated. It is important
to understand that the Archaic encompasses a range of human behavior in which some
degree of hunting and gathering was practiced.
Although the concept that preceramic cultures existed in the Southwest was
established early in this century (Kidder 1927), the term "Archaic" did not appear in
Southwestern literature until the late 1960s (Huckell 1996b; Irwin-Williams 1968a, b).
Prior to that time, preceramic cultures in the Southwest were defined by various local
artifact assemblages, grouped into small "complexes" or broader "cultures" and
"traditions." A more complete outline of the development of these concepts is
presented in Huckell (1996b). Those cultural-historical groupings which have had the
most lasting impact on Archaic archaeology in southern Arizona include the Desert
culture (Jennings 1956, 1957, 1973), the Cochise culture (Sayles 1983; Sayles and
Antevs 1941), the PICOSA and Oshara traditions (Irwin-Williams 1967, 1973, 1979),
the Southwestern Archaic (Irwin-Williams 1968a), the Pinto-Gypsum complexes or
cultures (Campbell and Campbell 1935; Harrington 1933; Rogers 1939) and, to a
somewhat lesser extent, the San Dieguito and Amargosa industries (Rogers 1939).
Each of these groupings is described briefly below, with particular attention paid to the
relationships with the archaeology of southern Arizona.
San Dieguito and Pinto-Gypsum
Over the course of several decades, Rogers (1929, 1939, 1958) revised what he
called the San Dieguito complex based on research he conducted in the Mohave
Desert. His studies focused primarily on surface sites and he based the relative ages
of three phases, San Dieguito I, II, and III, on presumed changes in artifact attributes
and the development of patina on artifacts. A rather thorough review of the changes
in Rogers' typological schemes is provided by Warren (1967). In addition to the
problems of interpreting assemblages based on surface distributions of artifacts,
Warren (1967) cautions against the use of chemical changes on artifacts as temporal
markers. To date, the only secure ages that can be assigned to the San Dieguito
complex come from Warren's excavation at the Harris site (Warren and True 1961),
originally excavated by Rogers in 1938. Three radiocarbon dates place San Dieguito
materials at the Harris site between 9000 and 8400 B.P. (Warren 1967).
The names originally derived for Rogers' San Dieguito phases II and III were
Playa I and Playa II, based on the surface distribution of flaked stone artifacts around
playas in the Mohave Desert. At around the same time as Rogers' studies, the
Campbells were excavating at sites in the Pinto Basin (Campbell and Campbell 1935)
and Lake Mohave (Campbell et al. 1937), and Harrington excavated at Gypsum Cave
(Harrington 1933). Each assigned names to projectile points found in these areas:
Pinto, Gypsum, and Lake Mohave. The presence of projectile point types at sites in
the Mohave Desert, in datable contexts, has given archaeologists in southern Arizona a
basis for determining the age of sites with Pinto and Gypsum or Gypsum-like
projectile points in Arizona.
Rogers (1939) defined the Amargosa tradition as the successor to and
concurrent with (for the early Amargosa I phase) the Pinto-Gypsum complex. The
Amargosa tradition was further refined by Haury (1950) based on excavations at
Ventana Cave and has been linked with Middle Archaic occupations there. Difficulty
by Haury (1950) in applying Rogers' San Dieguito terminology (review by Huckell
and Haynes, 1995) led to subsequent collaboration between Rogers and Haury
resulting in a three-phase sequence for the Amargosa tradition. Ventana Cave and the
Stahl site yielded stratified Amargosa materials, but no secure radiocarbon dates. In
addition to Pinto and Gypsum points, several kinds of corner- and side-notched
projectile points are associated with Amargosa II contexts. Ground stone implements,
scrapers, "sleeping circles," linear rock alignments, trails, and intaglios' are also
associated with the Amargosa tradition. Amargosa terminology is used,
predominantly, at the Ventana Cave site, which is discussed in greater detail below.
The Cochise Culture
A post-Pleistocene human occupation in southern Arizona was first recognized
in southeastern Arizona, where Sayles and Antevs in the 1940s utilized geologic and
archaeological investigations of the Sulphur Springs and San Pedro valleys and along
tributary streams to create a three-part sequence called the Cochise culture. The
original report (Sayles and Antevs 1941) suffered from poor distribution and
consequently never received the recognition it deserved (Dean 1987). As a
consequence, assemblages which may have been recognized as part of the Cochise
complex were often subsumed by terms given to other complexes, traditions, or
cultures. By the time the updated monograph was published (Sayles 1983), it was
already outdated. Nevertheless, its influence on our understanding of preceramic
cultural sequences in southern Arizona cannot be ignored.
Part one of Sayles' original (Sayles and Antevs 1941) three-part sequence
consisted of the Sulphur Spring stage (pre-8000 B.C.), characterized by simple slab
grinding stones and a limited chipped stone assemblage; these artifacts were found
associated with late Pleistocene faunal remains, interpreted as indicating a mixed
economy based on collection and processing of wild plants and on procurement of
large game. No projectile points were found with Sulphur Spring stage assemblages,
considerably limiting the recognition of this phase in other areas. The subsequent
Chiricahua stage (8000 to 3000 B.C.) was characterized somewhat more formally,
consisting of basin-shaped metates, hand stones and a more elaborate chipped stone
assemblage, including Chiricahua projectile points. Finally, the San Pedro stage (3000
to 500 B.C.) included implements from earlier stages as well as distinct side-notched
San Pedro projectile points and features such as hearths and cooking or storage pits.
Age estimates for these stages were provided by geologist Ernst Antevs, who
correlated his interpreted paleoclimatic record with North American and better
age-controlled European glacial and postglacial sequences. Though his ages were
remarkably close to subsequently radiocarbon dated sections (Waters 1986a), his
paleoclimatic intervals were based on "grossly oversimplified" reconstructions of the
relationship between alluviation and precipitation (Dean 1987).
Waters' (1986b) reinterpretation of Sayles' three-part chronology placed the
Sulphur Spring stage between 8000 and 6000 B.C., the Chiricahua stage between 1500
and 500 B.C., and the San Pedro stage between 500 B.C. and A.D. 1. He also
rejected Sayles' subsequently defined (1983) Cazador stage and, instead defined a gap
between 6000 and 1500 B.C. for which he argues little evidence for human occupation
exists (Waters 1986b). Whalen (1971) also rejected the applicability of the Cazador
One of the main themes of Sayles' three-stage culture-history was the idea that
Archaic hunter-gatherers became increasingly more reliant on plant foods and that they
invested more time in plant processing and associated technology. As they did, they
naturally became more sedentary, and eventually began cultivating plants.
The Desert Culture
Perhaps the most important contribution to the recognition of an Archaic
lifeway in western North America was Jennings' (1953, 1957; Jennings and Norbeck
1955) definition of the Desert culture. Jennings recognized that many of the Western
Archaic complexes were similar and attempted to equate these with the aridity of the
environment. Based on his excavations in the Great Basin, he described a 10,000-year
continuum of gathering-hunting-gathering from the end of the Pleistocene to the
historic period. This continuum was marked by sparse, small non-sedentary
populations living in caves or rockshelters, reliant on hunting, as well as small seed
harvesting and grinding. Economically, these groups exploited the environment
intensively, but were non-specialized. Although Jennings' interpretation was proposed
principally for the Great Basin, its emphasis on wild plant foods caused archaeologists
to relate it to regional variants such as the Cochise culture and the San Dieguito and
Amargosa industries.
PICOSA, Oshara, and the Southwestern Archaic
Several bold attempts to synthesize the diverse local assemblages in the
Southwest came from Cynthia Irwin-Williams. Her first attempt at synthesizing the
pre-ceramic cultural-histories of the Southwest was a sequence she named PICOSA
(Irwin-Williams1967). The acronym represented three geographically separate
traditions—Pinto, Cochise, and San Jose—which she grouped into "a continuum of
similar closely related preceramic cultures" (Irwin-Williams 1967:441). She noted
similarities between archaeological traditions from different parts of the Southwest, all
of which were being split into individual culture sequences, and which she linked
under a single acronym. She also argued that the economy and organization of these
groups was similar to the Desert culture of the Great Basin, but preferred to recognize
PICOSA and the Desert culture as distinct traditions. Based predominantly on the
recognition of projectile point types, her three divisions conform geographically with
the spatial distributions of later ceramic cultures (the Mogollon and Hohokam,
Anasazi, and Hakataya/Patayan).
Irwin-Williams' PICOSA and Jennings' Desert culture, were part of a
continental effort to make regional cultural-historical sequences more areally inclusive
(Huckell 1996b) and eventually led to the recognition and acceptance of the term
"Archaic" (Irwin-Williams 1968a,b). Like many archaeologists today, Irwin-Williams'
recognition of a regionally inclusive "Archaic" did not prevent her from continuing
efforts to refine regional sequences, one product of which is her Oshara tradition in the
northern part of the American Southwest (Irwin-Williams 1973, 1979).
...one can easily count on the fingers of one hand the archaeologists
who have devoted more than passing attention to preceramic
archaeology in the Southwest,.. .While this situation has been changing
over the last 15 years, it is interesting to note that general texts on
Southwestern archaeology have had little to say concerning the
preceramic period; ...
Huckell (1984a:2-3)
In the 13 years since Bruce Huckell made this statement, the process of
discovery has yielded abundant additional information about the "preceramic" or
Archaic Southwest. However, our knowledge of the middle portion of the Archaic
period is still sorely lacking. Although comparatively few sites have been found, the
diversity of sites found dating to the Middle Archaic hints that we have only scratched
the surface of an abundant source of data, particularly in the southern Basin and Range
Why So Few Middle Archaic Sites?
The paucity of archaeological sites dating to the Middle Archaic is owed, in
part, to several factors most easily summed up by three words: preservation,
identification, and discovery. As in the preceding Paleoindian and Early Archaic
periods, the passage of thousands of years can have profound implications for the
preservation of Middle Archaic resources. The passage of time affects not only the
preservation of the resources themselves, but also those things which act as context for
Middle Archaic archaeological remains (including geologic materials, contemporaneous
plant and animal assemblages, geographic features, etc.). With the passage of time, it
becomes increasingly difficult to reconstruct the environment from proxy data or to
reconstruct human behavior from the archaeological record.
The temporal dimension also influences our ability to distinguish between
Middle Archaic resources and those of other time periods. Certain artifact types, or
sometimes sets of archaeological resources such as lithic assemblages or clusters of
features, serve as "type fossils" for particular time periods. As time passes, parts of
those assemblages or artifacts are lost, destroyed, moved, or transformed. As detail is
lost from each site or activity area, we lose the ability to reconstruct the activities that
occurred there and to correlate those activities with other sites. For nearly all of
preceramic prehistory in North America, the most diagnostic artifacts are projectile
points; however, with further examination, features and assemblages can become
greater diagnostic tools, simply because they have more "staying power 2 ."
In southern Arizona, the ability to distinguish between Middle Archaic and
Late Archaic/Early Agricultural temporary campsites is difficult. As will be
demonstrated, so-called Middle and Late Archaic projectile points have been recovered
together at several sites. Whether these sites represent the accumulation of Middle
Archaic projectile points by Late Archaic groups or multi-component occupations at a
single locale is relatively immaterial. Either perspective suggests that Middle and Late
Archaic groups were utilizing the same environments and locations. One final note:
although the Late Archaic in the Tucson Basin has been recently renamed the Early
Agricultural period (Huckell 1995), based on growing evidence that the cultivation of
domesticated plants was a part of the economy, it is not clear yet whether Late
Archaic sites lacking evidence for cultigens represent another behavioral or economic
aspect of the same group(s) or whether they represent differing, but contemporaneous
groups utilizing the same general area.
Finally, with greater time depth, there is greater chance for deep burial of
archaeological resources. This can be a blessing, because it preserves not only the
archaeological resources but the contextual data used to interpret environmental
conditions and human behavior. However, greater time depth and deep burial can also
be a curse; older sites, by definition, are susceptible to more periods of erosion than
are younger sites and typical archaeological testing rarely exceeds a depth of 2 m (the
depth allowed by OSHA for a small trench). Fortunately, recent advances in
discovery techniques, including greater use of geoarchaeological prediction of
archaeological resource location, have added data to the sparse quantity of Middle
Archaic research.
Characteristics of the Southwestern Middle Archaic
There remain today few ways to segregate Middle Archaic from Early or Late
Archaic sites. The primary and most reliable means of separation is through an
absolute age estimate. Although estimates can sometimes be obtained by other means
(e.g., cation-ratio dating, obsidian hydration, dendrochronology), the technique that is
used most frequently is radiocarbon dating. Dates for the Middle Archaic period are
not entirely agreed upon, but there appears to be significant evidence to suggest that
this period dates to around 5500 to 3500 B.P. (Huckell 1996b). Further examination
of the geochronological implications of dating the Middle Archaic period are explored
below. These dates are often based on association with the next most frequently used
diagnostic tool for assigning age to a site: projectile point typology.
Often, there exist certain items that have not independently been established as
diagnostic of the time period under study, but that have typically been found with the
diagnostic items of that time period. These items should not be used as "diagnostic,"
but represent the characteristics of the time period. In the following sections, I refer
to these items as "hallmarks" of Middle and Late Archaic assemblages.
Projectile Points
Middle Archaic projectile point types are strongly tied to regional chronologies
outlined in the previous section. The recognition and dating of projectile point types
at sites across the West has been used as a way of relating sites which may be located
in geographically different regions, topographically different contexts, and containing
different assemblages of other artifacts and features. Several projectile point types
may serve as hallmarks of the Middle Archaic; these include: Chiricahua and other
side-notched types, San Jose/Pinto, Gypsum, and Elko. Each of these types may have
regional varieties. In addition, certain other projectile point types appear to exist only
within restricted regions. In southern Arizona, the Cortaro point may be indicative of
a Middle Archaic occupation (Roth and Huckell 1992; Sliva 1997). A long
tapering-stemmed variety, which appears to be different from Gypsum, has often been
classified as Early Archaic on the basis of radiocarbon dates from other regions
(Huckell 1984a); however, their recovery from numerous Middle Archaic contexts in
southern Arizona suggests that this point style may be affiliated with the Middle
Middle Archaic Features
Until recently, Middle Archaic features have been thought to be poorly
constructed or nonexistent. In the past few years, however, mounting evidence for
more formalized features has come from excavation of Middle Archaic sites.
Extramural features typically found at Archaic sites include basin-shaped hearths,
rock-filled pits, fire-cracked rock clusters, and ground stone caches (Agenbroad 1970;
Irwin-Williams 1973; O'Laughlin 1980; Windmiller 1973). A single possible storage
feature has been interpreted as part of a Middle to Late Archaic aged occupation near
El Paso, Texas (O'Laughlin 1980). The absence of storage features has been used as
evidence against an early adoption of agriculture; however, negative evidence cannot
be construed as evidence of absence. It is also possible that evidence for storage may
be better preserved in floodplain sites; future excavation of such sites may produce
storage features. Few inhumations have been found and the few known appear to
follow a pattern of burial practices. Two inhumations from the Tucson area were
recovered from beneath rock cairns (Dart 1986; Huckell 1996b). Although not all
Middle Archaic burials are found beneath these cairns, this trait also appears in Middle
Archaic burials in other parts of the Southwest (Mabry 1996b).
In addition to these small features, evidence appears to support the presence of
domestic structures in Middle Archaic sites. Although not an astounding observation,
the recognition of preserved Middle Archaic domestic structures confirms that shelters
are not solely a trait of later periods. Simple structures consisting of irregular outlines
and posthole patterns were first detected by Irwin-Williams (1973) in west-central
New Mexico. Huckell (1984a) has suggested that a rock alignment discovered on the
east side of the Santa Rita Mountains near Tucson, which he interpreted as a
windbreak, may be Middle Archaic in age. At the Tator Hills site in the Santa Cruz
Flats, the remains of a single "brush structure," consisting of a circular depression
filled with a dark homogenous, trash-filled sediment and surrounded by several
postholes located about the perimeter of the structure, appears to be associated with an
Archaic occupation surface on which Chiricahua and tapering-stemmed projectile
points have been recovered (Halbirt and Henderson 1993). Radiocarbon dates from
other features on this surface have given anomalous ages. Additional evidence for
shallow pit structures has been found in the central Rio Grande Valley (Schmader
1996), near El Paso, Texas (O'Laughlin 1980; Whalen 1994), and possibly near
Moquino, New Mexico (Beckett 1973).
Other Characteristics of the Middle Archaic
In addition to these hallmarks, Huckell (1996b) argues that rock art was
probably being created during the Middle Archaic. He suggests that Middle Archaic
rock art may include "linear geometric and representational elements," as well as
anthropomorphic figures. In addition to these forms of artistic or representational
expression, he notes that split twig figurines have been found in rockshelters in
southeastern California, northwestern Arizona, southern Nevada, and southeastern Utah
(Davis and Smith 1981; Emslie et al. 1987; Euler 1984; Janetski 1980; Schroedl
Middle Archaic Sites in Southern Arizona
The evidence for a Middle Archaic occupation in southern Arizona is quite
spotty and appears to be geographically biased toward bajada sites. Large surveys in
this area have identified several sites dating to the Middle Archaic. Areas that have
received little coverage include the floodplain and montane regions. By convention, 3
radiocarbon dates cited are expressed as uncalibrated radiocarbon years before 1950
(B.P.) 4 . Calibrated (calendar) ages are cited using the following abbreviations B.C. or
Ventana Cave
Ventana Cave is located in the Castle Mountains north of Sells, Arizona. Here,
Haury (1950) found a stratified sequence of cultural deposits dating from the early
Archaic (Huckell and Haynes 1995) through the present day. At the time of
excavation, the age of the deposits was based on geologic assessment of the site
deposits by Antevs, Hack, and Bryan (1951; cf. Haury 1950), all of whom had
different interpretations, and on correlation between artifacts found in the deposits and
their known associative ages at other sites. The "volcanic debris" layer contained the
oldest artifacts at the site, the Ventana Complex, and was considered related to Folsom
(Haury 1950) or Clovis (Haury and Hayden 1975). Geologic assessment of the ages
of subsequent materials in the "red sand" was based on this original correlation and
the depth of time represented by an erosional unconformity separating the Ventana
complex from the younger Ventana-Amargosa I deposits (containing stemmed
projectile points similar to those classified elsewhere as Jay points). Recent
radiocarbon dating and correlation of the artifacts with similar assemblages from the
Great Basin place this earliest deposit between 10,700 to 8700 B.P. or, narrowing the
margin based on evaluation and selection of the most reliable dates, between 9500 and
8700 B.P. (Huckell and Haynes 1995).
Overlying the Ventana-Amargosa I deposit was a midden (the "moist midden")
containing Middle Archaic (Haury's Chiricahua-Amargosa II) and Late Archaic
(Haury's San Pedro) artifacts. The midden was subsequently overlain by a second
midden (the "dry midden") containing Hohokam artifacts. Projectile points from the
Chiricahua-Amargosa II levels included San Jose/Pinto, and tapered-stemmed
(Gypsum) projectile points. The San Pedro levels contained San Pedro and Cienega
projectile points. Also found through these deposits were projectile points recently
classified as Cortaro (Roth and Huckell 1992). Roth and Huckell (1992) more fully
discuss the problems involved in using the Ventana Cave data. Unfortunately, no
radiocarbon dates have been derived from the midden deposits, presenting further
difficulty in correlating them with assemblages found at other sites of presumably
similar age.
Ventana Cave was likely used more-or-less continuously as a hunting camp
andJor possibly a base camp during the Middle and Late Archaic periods. Bayham
(1982) focused on the changing use of the cave from the Archaic to Hohokam periods
and concluded that the abundance of artiodactyl remains in more recent levels suggests
a change in the transport costs associated with sedentism. In other words, during the
Hohokam period, the cave was used as a hunting camp, because the relative cost of
transporting an entire deer carcass back to the base settlement would be too high.
Picaclzo Reservoir
Several Archaic sites are known from work near the Picacho Reservoir in
1983-1986 for the Tucson Aqueduct (Bayham et al. 1986). The sites are located at the
northeast edge of a broad flat plain called the Santa Cruz Flats, on the bajada of the
Picacho Mountains. A dune field covers a portion of the bajada and a small eroded
drainage (the "arroyo") crosses the dunes. At least three of the sites had substantial
Middle Archaic components; these include the Buried Dune site [AA:3:16 (ASU)], the
Arroyo site [AA:3:28 (ASU)], and the Gate site [AA:3:8 (ASU)]. Each appears to
represent a different type of activity, at least partially influenced by prehistoric setting
and by the potential for preservation in that setting.
The Buried Dune site consisted of several clusters of fire-cracked rock, which
have been interpreted as cooking features, and a low density scatter of flaked stone
and burned bone. At least some of the flaked stone raw material was acquired in
southwestern New Mexico. Projectile points are San Jose/Pinto varieties. The site has
been interpreted as a short-term field camp occupied during the winter or early spring.
Two radiocarbon dates on features from the Buried Dune site are 4300 ± 310 B.P.
(AA-673A) and 4290 ± 330 B.P. (AA-673B). A third radiocarbon date at the base of
the younger dune overlying this feature is 4000 ± 220 B.P. (AA-675).
A single locus at the Arroyo site consists of a dense midden, near what
archaeologists interpreted, based on the presence of cattail (Typha) pollen in the
midden (Gish 1986), as a Middle Holocene cienega (Bayham et al. 1986:365).
Geomorphologist Mike Waters (Bayham et al. 1986:365; Waters, pers. comm. 1996)
has argued that sedimentary and soil characteristics of this deposit do not indicate
cienega deposition. Middle Archaic projectile points consisted of Chiricahua and
tapering-stemmed points. Radiocarbon dates on features in the Middle Archaic locus
yielded dates of 4500 ± 100 B.P. (Beta-12267) and 3910 ± 290 B.P. (Beta-12270). A
third date at the base of the Middle Archaic midden yielded an age estimate of 4840 ±
100 B.P. (Beta-12268). Lithic resources and subsistence data point to use of local
resources over a relatively lengthy duration. The site has been interpreted as a
long-term base camp occupied principally during the summer and fall.
The Gate site has been interpreted as a base camp reoccupied repeatedly for
short periods of time. The site consists of a small Middle Archaic midden, a large
scatter of features and artifacts dating to both Middle and Late Archaic periods. Both
Chiricahua and Gypsum projectile points were recovered from the Gate site.
Radiocarbon dates are 4910 ± 95 B.P. (Beta-12271) and 4350 ± 90 B.P. (A-2964;
Czaplicki et al. 1984:42). A fourth site, AZ AA:3:9 (ASU) yielded a radiocarbon age
on a feature of 4140 ± 90 B.P. (Bayham et al. 1986).
Based on the presence of non-local raw materials and San Jose/Pinto varieties
at the Buried Dune site, Bayham and others (1986) make the argument that two
different groups, one regionally mobile and one locally mobile, were utilizing the
Picacho Reservoir area during the Middle Archaic period, and that locally mobile
groups reused the same sites into the Late Archaic period.
Santa Cruz Flats
Several Archaic sites are known from work at the southern margin of the Santa
Cruz Flats, near where the Aguirre Valley joins the Santa Cruz River (Halbirt and
Henderson 1993). The flats are named for the distal fan portion of the Santa Cruz
Valley, where outflow from the Tucson reach of the Santa Cruz spreads out over a
vast, flat plain.
Middle Archaic Pinto and Chiricahua style projectile points were recovered
from the Tator Hills site [AZ AA:6:18 (ASM)]. A Chiricahua and a stemmed
projectile point were associated with the oldest radiocarbon age estimate from the site
of 1890 ± 130 B.P. (Beta-25445)*. The site consisted of a concentration of artifacts in
association with the remains of a single "brush" structure, several thermal pits and
fire-cracked rock clusters, and likely represents a temporary, seasonal occupation.
Several Late Archaic San Pedro and Cienega style projectile points were
recovered from the Coffee Camp site [AZ AA:6:19 (ASM)] along with five Middle
Archaic Pinto and Chiricahua style projectile points. The majority of radiocarbon
dates from this site cluster around 2100 B.P. Three older dates [3120 ± 170 B.P.
(Beta-26352)*, 2870 ± 100 B.P. (Beta-27697)*, and 4040 ± 190 B.P. (Beta-27696)1
may represent an earlier occupation of the site; however, many of the dates are run on
mesquite charcoal' and dates of different ages are scattered throughout the
stratigraphy. A total of 354 features including pithouses, burials and pits were found
in three distinct geologic strata 6 . The site appears to represent a "semipermanent
camp, whose occupants exploited the resources of the upper and lower bajada, as well
as riverine and floodplain areas (Halbirt and Henderson 1993:375)."
Middle Archaic projectile points from both Tator Hills and Coffee Camp may
represent scavenged artifacts from earlier occupations. Their presence suggests,
nevertheless, that a Middle Archaic occupation was present somewhere in the vicinity
of the Santa Cruz Flats. The presence of Middle Archaic projectile points at other
sites within the study area and a radiocarbon age estimate of 4580 ± 80 B.P.' on a
roasting pit at site AZ AA:6:27 (ASM) further supports this possibility.
Harquahala Valley
Several Archaic sites are known from work in the Harquahala Plain, south of
Interstate 10 between Salome and Tonopah, Arizona (Bostwick 1988). The principal
drainage flowing through this valley is Centennial Wash, a tributary of the Gila River.
Middle Archaic projectile points were recovered from three of the ten sites
investigated. The majority of projectile points were Late Archaic in age. Apart from
a single corrected date of 7850 ± 400 B.P. (Beta-10959) from the Tortoise Sink site,
the only radiocarbon age estimates were Late Archaic in age. These other dates, 3000
± 120 B.P. (Beta-10957, The Lookout site) and 3290 ± 70 B.P. (Beta-10958, the
Apothecary site) date to the San Pedro period of the Late Archaic.
Like in the Santa Cruz flats area, the presence of Middle Archaic projectile
points does not necessarily indicate site age or duration of site occupation. Their
presence does suggest that the general area was utilized sometime during the Middle
Archaic period.
San Pedro, San Simon, and Sulphur Spring Valleys
In a study of the Middle and Late Archaic of the San Pedro Valley, Whalen
(1971) concluded that Archaic sites were located along river terraces and on the
piedmont. Most of these sites overlooked major stream channels or were near springs
or washes. Of his sample of 82 Archaic period sites, only six were Chiricahua
(Middle Archaic) phase sites. Recent investigations near Kartchner Cavern reiterate
the evidence for repeated seasonal occupation of these sites (Phillips et al. 1993).
While historic (Cummings 1927, 1928; Sayles and Antevs 1941) and more recent
surveys (Altschul and Jones 1990; Phillips et al. 1993; Whalen 1971, 1975) of river
valleys in southeastern Arizona have turned up numerous Late Archaic aged sites, few
Middle Archaic sites have been found and fewer yet intensively investigated.
The Lone Hill site (Agenbroad 1970, 1978), located in the piedmont west of
the San Pedro River, is comprised of multiple hearths, ground stone, and numerous
projectile points. Based on the presence of inverted basin metates, suggesting the
intent to return, Agenbroad concludes that the site was seasonally reused. One of the
metates was completely worn through, suggesting either single, long-term occupation
or intensively repeated seasonal occupation of the site.
Recent studies (Phillips et al. 1993) of a Middle Archaic occupation near
Kartchner Cavern at AZ EE:3:28 (the Kartchner Cavern site) have recovered a single
Clovis Paleoindian projectile point, as well as seven tapering-stemmed projectile
points, 12 Pinto points, a single Chiricahua point, a single Cortaro point, a handful of
later projectile point types, and numerous fragments or unidentifiable point types. The
site is interpreted as a lithic workshop that was reused throughout prehistory.
Sycamore Canyon and Rosemont Sites
Several Archaic sites have been discovered in the foothills and montane areas
of the Santa Rita Mountains, southeast of Tucson. Tagg and Huckell (1984) argued
for an Archaic component in Sycamore Canyon based on the presence of
tapering-stemmed, Pinto, and Cortaro projectile points and on similarities between
flaked stone discovered on those sites and at other Archaic sites. The features in
Sycamore Canyon all appeared to be much younger. The Sycamore Canyon sites are
located on the northwestern edge of the Santa Rita Mountains.
The Rosemont sites are located on the eastern side of the Santa Ritas, in a
drainage area which supplies Cienega Creek. The McCleary Canyon site (AZ
EE:2:102) consists of a small scatter of flaked stone tools and debitage, including San
Jose/Pinto style projectile points, a Cortaro point, and other later styles, and five
handstones. A shallow firepit was also found at this site.
The Wasp Canyon site (AZ EE:2:62) consists of five rock clusters and two
additional rock "structures." A radiocarbon date from the floor of a shallow pithouse
at the site yielded a date of 1990 I..- 370 B.P. (A-3103). Two Late Archaic corner
notched projectile points and fragments of two basin metates were recovered from the
immediate vicinity of this structure, further supporting a Late Archaic age for the
feature. A second feature consisted of an elliptical alignment of rocks which Huckell
interpreted as a simple brush structure or windbreak. A Pinto style projectile point
was recovered from the floor of this structure. Tapering-stemmed and Pinto projectile
points from the Wasp Canyon site suggest an Early or Middle Archaic age (Huckell
Tapering-stemmed, Pinto, and Gypsum points were also recovered from the
South Canyon site (AZ EE:2:82). Five additional features of clustered rock were
found at this site. AZ EE:2:87 yielded a mixed assemblage, including flaked stone
and four pieces of ground stone. Projectile points from AZ EE:2:87 include several
Pinto points and a "lozenge-shaped" projectile point, similar to the Gypsum form. A
single rock cluster was found at this site.
Among the most intriguing results of the Rosemont study is the fact that
Archaic period sites have been located in montane areas. These areas have seldom
been systematically surveyed. Huckell (1984a) also concluded that Early/Middle and
Late Archaic sites were differentially distributed. He found that Early and Middle
Archaic sites tended to be farther up the small montane canyons, while Late Archaic
sites were distributed down valley, closer to the piedmont. He suggested that
differences in site location may be due to changes in environmental conditions or in
subsistence practices.
La Paloma
Several Middle Archaic projectile point types (including the Cortaro, Gypsum,
and Pinto point styles) were recovered from excavated and surface contexts at the La
Paloma site and the nearby Pontatoc site. At La Paloma, Dart (1986) believed he
could stratigraphically separate this Middle Archaic component from a subsequent Late
Archaic component. Radiocarbon dates were not available for the Middle Archaic
component; however, carbonate development in the soils appeared strong enough to
support a Middle Archaic age estimate.
A stone alignment that may have served as a temporary structure and a circular
arrangement of fire-cracked rocks were the only features found associated with the
Middle Archaic aged artifacts. Pollen samples from the site suggested that the
Middle Archaic environment was roughly equivalent to that of the Late Archaic.
Chenopods, amaranths, spiderling, and wild buckwheat were present in these samples
and may have served as plant foods for this Middle Archaic activity area. Evidence
for seasonality was inconclusive, but Dart proposed that the site may have been
occupied during the early spring through autumn. Some lithic materials recovered
were obtained at considerable distance (60-100 km) from the site, suggesting either
mobility outside the Tucson Basin or interaction with groups outside the basin.
Dart concluded that the occupation at La Paloma represented "impermanent
annual settlement." Although he suggests that repeated use of the site during the
Middle Archaic may have been possible, the relative dearth of evidence for features
and extensive amounts of artifact debris directly related to the Middle Archaic suggest
that seasonal reoccupation may have not been so intensive.
Flying V Ranch
During the mid-1980s, three Archaic sites were found in the Ventana Canyon
area (Douglas and Craig 1986) during a survey of the Flying V Ranch. Middle and
Late Archaic projectile points were discovered at each of the three sites. The
diagnostic artifacts from all three sites were collected; however, only one of the two
larger sites was excavated and extensively surface collected. At least 19 projectile
points or fragments were recovered from this site (AZ BB:9:139, ASM). Based on
analysis of this single site, the area appeared to have been seasonally reoccupied by
Archaic groups since the Middle Archaic period. The Middle Archaic projectile points
recovered from the three sites include both Gypsum and Cortaro styles.
Tortolita Mountains Sites
Four Middle Archaic sites were found in the upper bajada of the Tortolita
Mountains during the Tucson Basin survey (Roth 1988, 1989). A fifth, previously
discovered by Hewitt and Stephen (1981), had been recorded prior to the survey.
Projectile points on these sites included Elko, stemmed, Pinto, Pelona, Chiricahua, and
Cortaro point types. Two Pinto points were recovered from the surface of another
Late Archaic site (AZ AA: 12:84; Roth 1995). These sites have been classified as
limited activity and small multiple activity sites (Roth 1989) and appear to have been
used by later occupations, as well.
Mountains Sites
Cortaro projectile points have been recovered from the upper bajada of the
Rincon Mountains (Simpson and Wells 1983). The sites tend to be located near
potential water sources. No features have been associated with these lithic scatters.
A vra Valley
Hundreds of Middle Archaic projectile points have been recovered from the
Avra Valley area (Czaplicki 1983; Dart 1987; Downum et al. 1986; Swartz 1987).
During a survey for the Central Arizona Project (CAP) Aqueduct, Downum and others
(1986) recorded a number of sites with Middle Archaic projectile points in dunes
located at the base of the Tucson Mountains. These areas also appear to have been
utilized during the Late Archaic. Middle Archaic projectile points have occasionally
been discovered eroding from alluvium exposed in entrenched portions of Brawley
Wash. Huckell (ASM site files) suggested that Middle Archaic artifacts eroding from
alluvium in Brawley Wash at the LaBoissiere site were reworked from the floodplain
surface. These conclusions have been supported by recent investigations (Lindeman
and Freeman 1996).
Santa Cruz River Floodplain Sites
Prior to excavation of the Los Pozos site (discussed in detail in Chapter 6),
firm evidence for a Middle Archaic occupation of the Santa Cruz River was extremely
scarce. Chiricahua style projectile points were recovered from AZ AA:12:86, a
predominantly Late Archaic site on the Santa Cruz floodplain. Haynes and Huckell
(1986, Huckell 1996b:338, pers. comm. 1997) have recorded a Middle Archaic site
near the Santa Cruz River south of Martinez Hill in Brickyard Arroyo (AZ BB: 13:70).
This site consists of several rock clusters, a small lithic scatter, an immature bison
skull, and a fragmentary Chiricahua projectile point. A single radiocarbon date from
the site has yielded a date of 4320 ± 120 B.P. (AA-2139). They have also reported a
possible Middle Archaic occupation along Ina Road, near the interstate, at AZ
AA:12:111, and a Middle Archaic component at the Joe Ben site (AZ BB:13:11), just
north of AZ BB: 13:70 in Brickyard Arroyo. A radiocarbon date on the lowest cultural
stratum at AZ AA: 12:111 yielded a date of 4260 ± 140 (A-2234); the stratum also
contained animal bone and fire-cracked rocks. The lowest cultural bearing stratum at
the Joe Ben site yielded three dates: 4850 ± 90 (A-1854), 3980 ± 100 (A-1783), and
4400 ± 220 (A-1853); however, the only diagnostic artifact found at the site was a San
Pedro (Late Archaic) projectile point (Haynes and Huckell 1986). At each of these
sites, strata containing flaked stone, fire-cracked rock, and animal bone have been
found. Hearths or other types of pit features are occasionally exposed.
The Cortaro Fan site (AZ AA: 12:486) is located at the distal portion of an
alluvial fan protruding from the Tortolita Mountains into the Santa Cruz floodplain.
During excavation of the site, Roth (1992) found numerous small surface or subsurface
features, including roasting pits, hearths, middens and clusters of fire-cracked rock.
Maize was recovered from some of the features and yielded radiocarbon dates of 2790
± 60 B.P. (AA-2782) and 2594 ± 90 B.P. (AA-2783). Three additional dates on
mesquite charcoal in roasting pits associated with maize are 2290 ± 240 B.P.
(A-4727), 2270 ± 50 B.P. (A-4728), and 2300 ± 100 (Beta-29803). In addition to
numerous other Middle Archaic projectile points recovered from this site are several
examples of the Cortaro projectile point type, which appears to date to the Middle and
Late Archaic periods (Roth and Huckell 1992; Sliva, 1997).
Status of the Middle Archaic in Southern Arizona
Our knowledge of the Middle Archaic period in southern Arizona has changed
a great deal during the past 10 years. Although the number of new discoveries of
Middle Archaic sites has not been large, the significance of those discoveries has
revolutionized the understanding of the Middle Archaic period. Radiometric dating of
previously discovered sites has confirmed the presence of Middle Archaic features and
artifacts in Santa Cruz floodplain sediments. These discoveries have conveyed a more
dynamic record characterized by the recognition of additional hallmarks, site types,
and site distributions.
New Hallmarks of the Southern Arizona Middle Archaic
As more sites are excavated new hallmark traits of the Middle Archaic are
discovered. With additional research, split twig figurines found in rockshelters and
caves on the Colorado Plateau may be found in other well-preserved contexts and
refinement of dating techniques may be used to determine the difference between rock
art from Middle Archaic sites and that from later periods. Among the most intriguing
discoveries, however, are the recognition of Middle Archaic features and additional
projectile point types. The presence of paleobotanical remains in Middle Archaic
features and the ability to recognize additional surface distributions of Middle Archaic
sites may, in the future, enhance our knowledge of the Middle Archaic and floodplain
resource areas.
Middle Archaic Features
Several criteria have been used to determine sedentism in the archaeological
record. These criteria include: larger site size, thick occupation deposits, and high
artifact densities; the presence of formal architecture, including ceremonial structures;
and access to critical resources, particularly water (Rafferty 1985). Investment in large
features, such as dwellings, is often used as evidence of permanence or
semi-permanence of residence (Eder 1984; Rafferty 1985; Stark 1981). The degree of
investment in dwellings must be considered (Whitelaw 1991), however, as brush
structures or circular rock "wind breaks" require far less investment in time and energy
than do formal pit structures. Storage and caching are also important components
when measuring the mobility of foraging groups (Binford 1980; Gilman 1987). These
types of features typically indicate repeated use of sites.
Although few dwellings have been recognized from Middle Archaic sites in
southern Arizona, the presence of these dwellings in other parts of the southern Basin
and Range may signify the potential for discovery of additional features of this type in
the Tucson Basin. New discoveries in the floodplain are likely to yield more of these
features due to the area's potential for preservation of the remains of these features.
Future discoveries may also be able to glean "hallmark" data from other
Middle Archaic features. Certain types of other features, such as pits, may become
more recognizable and their functions more interpretable. In addition, these features
yield important subsistence and temporal data that may be used to recognize the
differences between Early, Middle, and Late Archaic economy and mobility.
Middle Archaic Projectile Points
It is clear that additional research has yielded new "hallmark" projectile points
for the Middle Archaic period. The appearance of tapering-stemmed (thought to be
Early Archaic) and Cortaro (thought to be Middle or Late Archaic; cf. Roth and
Huckell 1992) projectile points repeatedly at sites dating between 5500 and 4000 B.P.
may signal the presence of two additional diagnostic types. The presence of the
Cortaro point in undeniably Middle Archaic contexts at the Los Pozos site appears to
confirm its legacy as a Middle Archaic hallmark.
Projectile points may also indicate the presence of groups practicing two
distinctly different patterns of mobility. The research conducted by Bayham and
others (1986) at the Picacho Reservoir, by Roth (1995, 1996) in the Tortolitas, and by
Huckell (1984a) in the Santa Rita Mountains seems to suggest that certain Middle
Archaic groups were practicing a more limited pattern of mobility. These groups may
have already been tethered to smaller regions, accessible to both floodplain and upper
bajada environments, a pattern that continued into the Late Archaic/Early Agricultural
Middle Archaic Site Types and Site Distributions
The idea that some Middle Archaic sites in southern Arizona mark groups
tethered to certain resources is further supported by studies of subsistence data from
Middle Archaic sites (Bayham et al. 1986; Huckell 1984a; W6cherl 1997). Although
numerous Middle Archaic limited activity sites have been discovered, additional sites
supporting repeated use of sites and site areas have been discovered.
The presence of sites in floodplain localities which would offer abundant wild
plant foods signals an important change in the relationship between environment and
human occupation. The discoveries at Los Pozos and Cortaro Fan may suggest that
the fortuitous discoveries of past decades are but a minor manifestation of a potential
larger-scale occupation of the floodplain. Future discoveries along channel margins
and in distal fan reaches where entrained sediment from incised reaches is allowed to
accumulate are likely to reveal additional Middle Archaic floodplain occupations.
Some Middle Archaic sites may also be preserved at deeper stratigraphic levels;
however, new archaeological testing and data recovery techniques will have to be
developed before these deeper deposits can be explored. Just five years ago the
number of Late Archaic floodplain sites was very small, but today we recognize an
almost continuous occupation of the floodplain by Early Agricultural populations
during that period.
The environment of the Santa Cruz River may have provided the initial
conditions to support reduced mobility during the Middle Archaic. The presence of
archaeological sites in the floodplain, a pattern of repeated site use, and tethering to
certain resource areas create a pattern of site distribution and site use that is amplified
during the Late Archaic/Early Agricultural period. This pattern has important
implications for the transition to agriculture in the Tucson Basin.
Volumes have been written on the Late Archaic period in southern Arizona
(e.g., Eddy and Cooley 1983; Gregory 1997b; Huckell 1995; Mabry 1996a; Sayles
1983). The following section highlights features that distinguish it from the preceding
period. For the purposes of this discussion, I follow the chronological scheme
presented by Huckell (1995) and utilized by Mabry (1995), which classifies sites with
the earliest evidence for agriculture as the "Early Agricultural Period."
Investigations of Late Archaic/Early Agricultural Sites in Southern Arizona
The Late Archaic, late preceramic, late preagricultural, and Early Agricultural
periods, as they are variously defined, are encompassed under the San Pedro phase of
the Cochise Culture. The same periods from nearby regions include the Fresnal and
Hueco phases of the Chihuahua tradition in Mexico (MacNeish 1993) and the Armijo
and En Medio phases of the Oshara tradition (Irwin-Williams 1973).
Early Investigations
The San Pedro phase was first defined on the basis of artifacts and features
found at the Fairbank and Charleston sites in the San Pedro Valley (Sayles and Antevs
1941; Sayles 1983). The Fairbank site contained only small storage and cooking
features and provided no evidence for agriculture. Initial studies of this phase
suggested that Late Archaic groups were mobile hunters and gatherers following a
seasonal pattern of repeated site occupation. Pit structures were found at the
Charleston site after publication of the original report (Sayles 1983).
Evidence of agriculture came later, with Eddy and Cooley's excavation of sites
in the Cienega Valley (Eddy 1958; Eddy and Cooley 1983). In addition to maize, the
features found at the San Pedro Cochise 8 phase AZ EE:2:35 (ASM), Donaldson and
Los Ojitos sites included small round pit structures, hearths, cooking and storage pits,
and middens.
Defining the Early Agricultural Period
As more Late Archaic sites were discovered, increasing evidence existed that
sites dating to this time period fell into two distinct groups: those having evidence for
agriculture and those without evidence for agriculture. Although some non-ceramic
sites are difficult to place in time, the securely dated Late Archaic sites in the Tucson
Basin were remarkably consistent in the presence of maize (Fish et al. 1990; Roth
1989). Moreover, the ubiquity of maize at these sites often exceeded that of the later
Hohokam period. Few of these sites in the upper portion of the bajada have been
excavated and only one of them has exhibited evidence of agriculture. A pollen wash
on a mano found at the La Paloma site revealed evidence of maize pollen. Roth
(1995) has suggested that sites on the bajada surrounding the Tucson Basin may
represent use of the area during logistical trips from central habitation sites in the
floodplain. Of the many sites dating to this time period, perhaps one of the best
examples of an apparently non-agricultural site is the Coffee Camp site (see above,
Halbirt and Henderson 1993). Coffee Camp epitomizes the problem of distinguishing
between a Late Archaic "base camp" and an Early Agricultural period "logistical
Huckell (1995) recognized the "ecological" problem inherent in classifying sites
of clearly agricultural economy together with sites that lacked evidence of
domesticates, and proposed the resurrection of a concept that was proposed more than
40 years prior (Martin and Rinaldo 1951; Woodbury 1993). The Early Agricultural
period, as Huckell (1995) conceived it, was comprised of two phases: San Pedro
(1500-1200 B.C. to 500 B.C.) and Cienega (500 B.C. to A.D. 200). Huckell based his
assignment of a new period on the mounting evidence for Early Agricultural
populations in the Tucson Basin at the Milagro site (Huckell 1988, Huckell et al.
1994), the Cortaro Fan site (Roth 1992), the Clearwater site, 9 the sites along the Santa
Cruz River, 10 and at other sites with evidence for early agriculture. He also based
much of this new period on reinvestigation of the Fairbank site in the San Pedro
Valley (Huckell 1990) and the Donaldson and Los Ojitos sites in Matty Canyon
(Huckell 1995).
New Discoveries along the Santa Cruz River
In the past two years, additional Early Agricultural sites have been found along
the Santa Cruz River, within the study area. Nearly all of these sites are located on
the Holocene terrace (t2, Figure 2.1). Those that are directly related to
geoarchaeological investigations within the study area are discussed in Chapter 4, and
include the cluster of sites along Ina Road (AZ AA: 12:103, 111/688, and 503), and the
Rillito Fan (AZ AA:12:788) and Clearwater (AZ BB:13:6) sites. Information on
archaeological sites within the focus area is presented in Chapters 5 and 6. Because
the analyses of Square Hearth (AZ AA:12:745), Stone Pipe (AZ BB:13:425), and
Santa Cruz Bend (AZ AA:12:746) have been presented in a synthetic volume, the
three sites are discussed together in Chapter 5, along with archaeological testing at the
Juhan Park site (AZ AA: 12:44), located on the opposite bank of the river, in this area.
t AA:12:85
Ireerna cer--arcelsoratil
ch. y
O. or arbt
difil Archaeological site
II Desert Arch000logy. i;gi
Figure 2.L Distribution of archaeological sites in the study area and their location on the
Holocene (Qt2) terrace. For descriptions of geologic units (after McKittrick 1988), see
Appendix A.
A discussion of the Los Pozos (AZ AA:12:91) and Wetlands (AZ AA:12:90) sites is
presented in Chapter 6.
Florescence of the Early Agricultural Period
Many of the excavated sites dating to the Early Agricultural period are large
and contain numerous pit structures and extramural pit features. Few of the pit
structures overlap, suggesting that the sites were repeatedly occupied over a short
time-span, and many of the pit structures form what appear to be house groups (Mabry
1996a). Possible communal structures have been found at the Santa Cruz Bend site
(Mabry 1996a) and the Wetlands site (Freeman 1997). Maize ubiquity values
(frequency of contexts in which maize is present) at these sites are consistently very
high (see Table 2.1), indicating that maize constituted a substantial portion of the
prehistoric diet.
Table 2.1
Presence of Carbonized Maize Remains at the Middle Santa Cruz
River sites.
No. of Samples
Presence Value
Santa Cruz Bend*
Early Agricultural
Stone Pipe*
Early Agricultural
Early Ceramic
Early Ceramic
Los Pozos**
Early Agricultural
Early Agricultural
Square Hearth*
* Analysis by L. Huckell (1996).
** Analysis by M. Diehl (1997a, 1997b).
Time Period
The majority of sites dating to this period fall between 2500 and 2000 B.P.,
although a San Pedro-type pit structure was recently discovered at the Wetlands site
(Freeman 1997)." There appear to be significant changes in site structure over the
Cienega phase (800 B.C.-A.D. 150) that may reflect temporal changes in site use and
that appear to correspond with seasonality of occupation (Freeman 1997); however,
additional excavation will be needed determine whether these patterns hold.
In addition to these Early Agricultural localities, a number of sites in the Santa
Cruz floodplain display evidence for early ceramic technology. Sites dating to this
later time period have been designated using the term "Early Ceramic period," and
Mabry (1996a) has modified the cultural chronology to reflect those changes (see
Table 1.1). Recent excavations have demonstrated, however, that the earliest evidence
for ceramic production extends into the early Cienega phase (Diehl 1996b; Freeman
Altogether, these new discoveries suggest that the Early Agricultural period
floresced during the Cienega phase. During the early part of this phase it appears that
use of sites (such as Clearwater and Wetlands) was more highly seasonal with
occupations during the late summer or early fall (Freeman 1997), while occupations
later at Santa Cruz Bend, Stone Pipe, and Los Pozos sites may reflect a year round
occupation (Gregory 1997b; Mabry 1996a).I2
Long-term changes in climate are presumed to have had a great effect on
geologic systems, particularly rivers. The changes in climate reflected by Holocene
alluvium also mark changes in the environment to which human groups sometimes
responded. Geoclimatic intervals, therefore, such as early, middle, and late Holocene,
have often been used as criteria for defining boundaries between long-term changes in
human activities. Unfortunately, these geoclimatic periods are also poorly-defined and
there is a deplorable lack of consensus about how to interpret and designate these
intervals. The period marked by Antevs' (1948, 1953) Altithermal appears to represent
a significant set of changes in geologic and climatic parameters. In southern Arizona,
the onset of this period seems to be marked by a complete lack of human occupation
(Berry and Berry 1986; Irwin-Williams and Haynes 1970; Waters 1986b). A recent
inventory of Paleoindian and Archaic sites has indicated, in fact, that a "middle
Holocene" occupation of southern Arizona is virtually nonexistent (Mabry et al. 1997).
As climate apparently ameliorated toward the end of this period, the first
"Middle Archaic" occupations occur. If an Altithermal abandonment took place, then
there is apparently a lack of continuity between Early and Middle Archaic occupations
in southern Arizona. Southern Arizona could have been re-occupied by groups with
no previous knowledge of the area or by groups that occupied the area thousands of
years before or both. Each of these scenarios may involve groups with similar or
different economies, therefore, it is important to consider both origin and economy in
any analysis of post-Altithermal human response. The following section addresses the
ways in which archaeologists have interpreted human response to the Altithermal
drought and the implications this has for examining post-Altithermal groups in
southern Arizona during the Middle to Late Archaic transition.
Antevs' Altithermal
Antevs (1955) defined the Altithermal as a hot, dry period lasting from
approximately 7000 to 4500 B.P. He based this interval on data supporting lake
desiccation, stream entrenchment, eolian erosion, and soil formation in the Great Basin
and the American Southwest (Grayson 1993). Today, we recognize that climatic
change during this period following the onset of the Holocene affords more complex
interpretation than Antevs' original definition and that the timing of these changes may
not be concurrent across elevational and latitudinal gradients. For example, Davis and
others (Davis 1984; Davis et al. 1986) have suggested that multiple thermal maxima
explain the differences in timing of vegetation changes for low versus high elevation
sites. During these maxima, summer temperature probably increased by 2 degrees C.
The first real contest to Antevs' hot, dry Altithermal was advanced by Martin
(1963) who used palynological data from southern Arizona and modern atmospheric
circulation patterns to advance the idea of a warmer, but wetter Altithermal.
Mehringer (1967) subsequently challenged Martin's results, demonstrating that
evidence for increased effective precipitation came from strata younger than 5400 B.P.
However, Martin's proposal that increased solar radiation promoted intensified
monsoonal circulation has retained some credibility (Van Devender 1987; Van
Devender et al. 1984; but see Spaulding 1991). What remains at question, at least for
the American Southwest, is whether or not intensified monsoonal circulation of
precipitation results in increased effective moisture.
The idea of a hot, dry Altithermal has received support from palynology (cf.,
Hall 1985), alluvial cutting and filling events (Haynes 1968; Waters 1986a), lake
desiccation (Waters 1989), eolian deposition and soil formation (Holliday 1989;
Monger 1995), and packrat middens (Spaulding 1991). Moreover, human use of the
landscape, as well as humanly-produced water control features, seem to indicate that
the middle Holocene was dry in the American Southwest and perhaps elsewhere in
North America (Waters and Kuehn 1996). Erosion of small streams in western Iowa
(Bettis and Hajic 1995; Bettis and Thompson 1981, 1982; Thompson and Bettis 1982)
provides potential geologic evidence for widespread climatic changes during this
period, but it also removes or fails to preserve the archaeological records of human
response to these changes that can be found in certain landscapes. Similar erosive
forces have been cited as the cause of missing archaeological site records for the
Middle Holocene in southern Arizona (Waters 1986b).
Correlate Human Responses
Meltzer (1991, cf., Evans 1951) has recently made a case for a correlate human
response to Altithermal climatic change. In West Texas, he discovered more than 60
prehistoric water wells, dug from an "Altithermal surface" to the receding water table
below. These wells and their stratigraphy provide evidence that the warm, dry period
during the Altithermal was pronounced enough to create drought conditions. And,
although Holliday (1985) suggested early in his investigations of soils on the southern
High Plains that there were two droughts during the Altithermal, he more recently
recanted (1989) this earlier hypothesis, claiming that the Altithermal period is more
complex than originally suspected. Evidence for the onslaught of the Altithermal
comes from a marl at the Mustang Springs site, near Midland, Texas; diatoms in the
marl suggest slow, shallow, slightly saline water. Although the top of the marl unit
("Altithermal surface") is highly eroded, marl deposition seems to end concurrently
with the beginning of eolian deposition, around 6900-6800 BP. Well-digging behavior
probably began shortly after. A similar record of well-digging behavior has been
recorded by Haynes (1995) at Blackwater Draw. Utilizing geologic records associated
with the Blackwater Draw wells, Haynes describes the erosional and hydrologic
evidence supporting this interpretation. One of the most important aspects of
archaeological research that both Haynes and Meltzer bring to light is how
archaeologists make decisions about whether humans are actually responding
behaviorally to climatic stress:
...before concluding that the presence of Altithermal-age site is evidence of an
adaptation to drought, one must determine,.. .the degree (if any) of ecological
and climatic stress.. .Then, those selective factors must be linked directly to
human adaptive responses detected archaeologically. Too often efforts to link
Alithermal climates with a human response do not go beyond showing that
certain cultural patterns are roughly "compatible" with a model of severe
drought...(Meltzer 1991:237).
During the Altithermal, there is evidence for bison population decline on the southern
High Plains (Dillehay 1974; MacDonald 1981). Although Reeves (1973) infers, on the
basis of data from only a few sites on the northern Plains, that there is little evidence
for a reduction in the number of bison. Additionally, it has been suggested that bison
underwent evolutionary change during the Altithermal, with the resultant form (smaller
Bison bison) surviving this period (Frison 1991; Reher 1979). Benedict and Olson
(1978) propose that the Mount Albion complex of Colorado may hold the answer to
where these bison and the people subsisting on them went during the Altithermal.
They argue that the timberline environment may have been a "refuge" for both humans
and animals during this drought period. Dillehay (1974) claims that bison population
on the southern Plains declined again from A.D. 500-1200.
Altithermal Abandonments?
Following Antevs' definition of a hot, dry Altithermal, several authors (Berry
and Berry 1986; Huckell 1996b; Irwin-Williams and Haynes 1970; Mabry 1996a;
Waters 1986b; Waters and Kuehn 1996) have suggested that human groups in southern
Arizona may have abandoned the area at the onset of the Altithermal. Preliminary
analyses of site distribution data for identified and recorded Early and Middle
Holocene indicates that there is a significant reduction in the number of sites dating to
the Middle Holocene and that most of the Middle Holocene sites identified in Arizona
are located on the Colorado Plateau (Mabry et al. 1997). This could, in part, be due
to the lack of ease in identifying assemblages dating to the Middle Holocene, though a
scan of the available data suggests this is unlikely (Mabry, pers. comm. 1997).
Furthermore, the distribution of archaeological sites is highly dependent on the
geomorphic processes that have altered the landscape during the Holocene period
(Waters and Kuehn 1996). A similar argument was made for an abandonment of the
High Plains during the same time period, before all the data were in (Frison 1991).
Are we just not recognizing Middle Archaic sites dating prior to 5500 B.P? Were
occupations present, but the remains of them swept away during erosion of river
channels? Or, has the density of hunter-gatherers in southern Arizona always been so
light on the landscape that a gap is apparent rather than real?
Whether or not there is a gap in occupation of southern Arizona during the
Middle Holocene, there appears to be sufficient reason to believe that humans would
have been influenced by climatic changes. The current evidence for southern Arizona
suggests that human occupations changed rather drastically. This is further supported
by studies of modern hunter-gatherers under drought conditions»
Modeling Forager Response to Altithermal Drought
The general !Kung strategy is to camp in an area where a mix of
resources - including water, plant, and animal foods - is readily
available. Shifts in campsite reflect changes in food preference, the
availability of new vegetable resources, or new knowledge about the
location of wide-ranging and constantly moving large game... .Of course,
in all such moves, water is the major, and most limited factor.
(Yellen 1976:56-58)
Water is, indeed, one of the most limiting variables in forager strategies,
particularly in arid and semi-arid settings (Meltzer 1995). Forager responses to severe
droughts can include range shift or expansion, aggregation at permanent water sources,
or abandonment (Meltzer 1995). Each of these strategies should have distinctive
archaeological consequences.
In an effort to provide explanation to the evidence he gained from examination
of Altithermal archaeological sites on the Southern High Plains, Meltzer (1995)
developed a four-part model of Altithermal "adaptive strategies," based on examination
of modern forager response to drought. He assigned names to the four types of human
groups which would practice such strategies: hardscrabblers, collectors, wayfarers, and
expatriates. Hardscrabblers are groups who remain in the region, despite the scarcity
of resources. Collectors abandon the region, but annually or intermittently return to
the region for certain resources. Wayfarers represent groups that abandon the region,
only passing through it to get to another place (sensu Meltzer 1995) or may represent
groups who have never lived in the region, but pass through it on the way to another
place. Expatriates represent groups who, over time, abandon the region in favor of
another, more suitable, territory.
Two of these strategies, wayfarer and expatriate, would result in ephemeral
sites with few, if any, identifying characteristics. The most identifiable characteristic
would be a few water wells, at irregular depths. Collectors and hardscrabblers, on the
other hand, leave more identifiable traces of their presence on the landscape. For both
collectors and hardscrabblers, wells should be more numerous and appear in clusters.
Other features and artifacts should also be more numerous. Though erosion could
account for some site loss, it is likely that the lack of sites dating to the middle
Holocene in southern Arizona is the result of poor identification or erosion of
ephemeral site types produced by wayfarer or expatriate strategies.
Modeling Post-Altithermal Foraging Strategies
Post-Altithermal forager response, presumably what has been called the Middle
Archaic, is partly dependent on landscape use during the Altithermal drought period.
Hardscrabblers and collectors, whose knowledge of the formerly drought-stricken
region would be superior to those who either abandoned the region or who travel
across it ephemerally, would presumably be quicker to identify favorable changes in
the region, while wayfarers and expatriates would require longer time to become
acquainted with the landscape and its available resources. Hardscrabblers and
collectors would be well aware of raw materials located near their settlements.
Wayfarers and expatriates, on the other hand, may spend a considerable amount of
time exploring the region, resulting in a scattered distribution of sites. Exotic raw
materials would comprise a significant portion of their assemblages. A lag in human
response by any of the four idealized groups is unlikely to be geologically visible.
The forces that drive human groups not living in a drought-stricken region
(every group except "hardscrabblers") to claim or reclaim these territories under more
favorable (wetter) climatic conditions is critically important to the evaluation of their
post-drought strategies. A model that evaluates one such force was proposed by
Huckell (1990) to account for the Middle to Late Archaic transition.
Huckell's (1995:16) defined Early Agricultural period is marked by evidence he
cites for the "initial appearance of agriculture between 1500 B.C. and 1200 B.C." The
growth of this conceptual scheme is first expressed best in his dissertation (Huckell
1990). Although he argues that evidence for the earliest appearance of agriculture in
southern Arizona (the San Pedro phase of the Early Agricultural period, 1200-800
B.C.) portrays a mixed farming-hunting-gathering economy, he also cites evidence
from architecture and material culture to suggest that this stage "appears to represent a
surprisingly advanced stage in the transition from hunting and gathering to agriculture
(Huckell 1990)".
Huckell (1990)' 4 proposed that environmental conditions along river valleys
began to improve at the end of the Holocene Altithermal, and that these improved
conditions eventually led to the settlement and exploitation of these environments by
immigrant groups of farmer-foragers. He further suggests that northward trending
river valleys from northern Mexico into the Southwest would have provided a "natural
corridor" for such migration. Huckell (1990) acknowledged the need to "establish the
exact nature of the conditions along these rivers between 3,000 and 5,000 years ago."
The distribution and recognition of Middle Archaic archaeological sites in the
floodplain and their material evidence from those sites suggest that Huckell's argument
may not be as simple as originally proposed. Middle Archaic groups occupying the
floodplain immediately following the end of the Holocene Altithermal signifies
recognition of this resource area by the first (or indigenous) groups in southern
Arizona. The nature of this evidence is presented in Chapters 6 and 7, and has
profound implications for understanding the Middle to Late Archaic transition.
1. Also called "geoglyphs," these are alignments and/or clearings of rock that are
formed to create geometric, anthropomorphic, or zoomorphic designs.
2. Flaked and ground stone assemblages have greater frequency on the landscape,
while features are more likely to be preserved. Additional examination of these two
types of archaeological data, with a keen eye for trends in the co-occurrence of feature
types, artifact types, or the distribution of these materials, could create patterns that are
characteristic of certain time periods. The preservation of botanical or faunal materials
in features could then be used to establish radiometric ages for such patterns.
3. Convention established by the Twelfth International Radiocarbon Conference,
Trondheim, Norway, 1985. Departing from this convention, I have chosen to use the
terms B.C. and A.D. rather than cal B.C. and cal A.D. and do not list the calibration
curve used when citing the work of previous authors who have not reported this
4. Ages from Beta Analytic, Inc. are cited using the age estimate after correction for
813C. In cases where the original site report did not give both measured and
8 13C-corrected age estimates from Beta Analytic, Inc., it is assumed that the original
publication has cited the 6 13C-corrected age estimate; however, these ages are marked
with a star (*). Readers should consult either the original publication, the author of
the volume from which the dates are cited, or laboratory-published date lists for
radiocarbon date information.
5. Schiffer (1986) has demonstrated that mesquite charcoal can provide erroneous age
estimates. Mesquite that has been dead for several hundred or even 1,000 years can
be found on the desert floor. This old wood may have been particularly handy as
firewood since green mesquite is very tough, making it difficult to remove branches
from a live tree. A radiocarbon sample would date the death of the tree, rather than
the cultural event, making the age of the charcoal erroneously old.
6. Geological investigations of the Coffee Camp site were carried out by Keith
Katzer, but the relationships between geologic strata and pit features was established
by the archaeologists after fieldwork was complete by projecting feature elevations
across the site and "correcting" those elevations based on the presumed conformability
of geologic strata. However, the geologic strata need not be conformable or
continuous across the site. It is difficult to tell whether the mixed radiocarbon ages of
some strata are due to radiocarbon date error or error in stratigraphic placement of the
7. The original report (Halbirt and Henderson 1993) gives neither lab number nor
information on the nature of this date. It is assumed that the date was run at Beta
Analytic, Inc. and that the reported age is corrected for •313C.
8. Huckell (1995) would later define the Cienega phase of the Early Agricultural
period on the basis of excavations at these sites.
9. The Clearwater site was at the time comprised of the San Agustin Mission site, the
Brickyard site, and the Mission Road site. For the purposes of simplicity and
distinction from historic occupations of the same area, the Early Agricultural
component of the site has been renamed "Clearwater" (Doelle 1996).
10. At the time of Huckell's publication, only Santa Cruz Bend, Stone Pipe, and
Square Hearth had been excavated (Mabry and Clark 1994; Mabry 1995). Square
Hearth is not included in the Early Agricultural Period.
11. A radiocarbon date on this feature yielded an age estimate of 2790 ± 50 B.P.
(Freeman 1997), falling within the expected range of dates for the San Pedro phase.
The remainder of the features at this site were early Cienega phase in age.
12. Each of these later Cienega phase sites shows evidence for occupation in spring,
summer, and fall. There are no winter indicator plants, making it difficult to
absolutely assign these sites to year-round use.
13. Meltzer (1995) has conducted a rather thorough review of the anthropological and
ethnoarchaeological literature, surveying specifically for studies of how modern
foragers respond to drought conditions. Some of the key points are highlighted in the
following section.
14. The highlights of Huckell's (1990) argument are presented in this discussion.
Those interested in this interpretation should refer to his dissertation for a more
complete discussion.
...the present is the key to the past...
This simple statement, often cited as the definition of uniformitarianism, once
caused great anguish in fluvial geomorphology, particularly among those who observed
that extreme flood events did not occur in historical records (Baker 1988a, b).
However, "uniformitarianism in its twentieth century form... [proposes only that an
hypothesized event]...obeys the laws of physics [or of human behavior] and is
consistent with the field evidence (Baker 1988a, b)." This dictum is useful both in
archaeology and geosciences. In order to utilize this principle, the geologist or
archaeologist must first understand the laws or rules under which natural or human
systems operate. These laws are defined on the observation of modern and historic
stream processes and on the documentation of the effects of those processes preserved
in historic and prehistoric alluvium.
Desert stream systems create particularly dynamic stratigraphic records.
Fluvial processes preserve archaeological sites and geologic deposits, but can also be
erosive, removing parts of the archaeological and geological records that may have
been preserved otherwise. In the course of its history, natural processes of the Santa
Cruz River have exposed preserved portions of this record. Archaeologists and
geologists have recorded these natural exposures as well as exposures artificially
revealed by modern construction activities. We now have a good record of
archaeological and geologic events on the Santa Cruz River over the past 8,000 years.
In addition to the prehistoric sedimentary record, we also have a historic record
of meteorological events and their effects on the character of the Santa Cruz River.
Like archaeology, geology uses analogy to determine what prehistoric landscapes were
like. From analogical reasoning, geologists are able to develop models based on the
physical characteristics of modern systems. Because the known conditions of the
Santa Cruz do not always reflect the possible past conditions of the stream, it is
sometimes necessary to model those conditions using a number of different sources of
The purpose of this chapter is to outline the laws or rules under which desert
streams operate, and to examine the known hydrologic processes that act on the Santa
Cruz River specifically. Five types of paleohydrologic data are typically used to
reconstruct river behavior:
(a) historical reconstructions, which use non-systematic historical
records to reconstruct flow conditions; (b) regime-based reconstructions,
which use properties of the drainage network or channels to infer past
flow conditions; (c) palaeocompetence reconstructions, which relate
characteristics of channel sediments to flow parameters; (d) geobotanic
methods, in which the characteristics of vegetation along the channel are
used to reconstruct flow history; and (e) paleostage indicators, which
record the stage of individual flows (Wohl and Enzel 1995:24).
This dissertation utilizes data from most of the above parameters as well as from the
archaeological record to interpret the sedimentary and stratigraphic record left by the
Santa Cruz River.
Paleocompetence reconstructions focus on the relationship between streamflow
and sediment characteristics. Typically such reconstructions involve calculation of
discharge estimates based on a number of variables including channel width and depth,
and valley slope. Discharge estimates are dependent, in part, on local variables such
as sediment source, transport mechanisms, resisting forces such as vegetation and
geology, and precipitation. Because of the incomplete nature of prehistoric alluvial
records, it is generally inappropriate to calculate discharge estimates.
Paleocompetence can be inferred, however, based on knowledge of the local variables
that affect a particular stream and on flow conditions necessary to produce given
sediment characteristics. What follows, therefore, is a general discussion of flow
conditions in desert streams and the kinds of sediment characteristics that are used in
southern Arizona to make inferences about paleocompetence.
Desert Stream Processes
Desert streams operate in a unique manner (Graf 1988a). The main difference
between streams in humid and dry regions is, of course, precipitation. Precipitation can
work together with a number of other variables, including vegetation, topography,
lithology, temperature, geologic structure, and human behavior in determining
operation of stream systems. Precipitation and temperature affect the kind and number
of plants supported. The small number of plants near desert streams allows
precipitated moisture to flow (as runoff) virtually unhindered into the stream system,
so that water received by the stream system arrives with a higher energy to entrain and
transport sediment (Parker 1995). The kind of vegetation supported by desert
precipitation can also have an effect on sediment entrainment. Desert plants produce
less debris than plants in humid regions, inhibiting pedogenesis (Bull 1991). As a
result, unconsolidated sediments near stream channels are more likely to be entrained
by the energetic desert stream system.
Flow conditions also differ between streams in dry and humid regions. Desert
streams experience intermittent flow in some or all reaches and tend to react quickly
to extreme flow events, enhancing the spatial and temporal variability of streamflow.
The great variability in discharge in dry region streams (Baker 1977; Chippen and Bue
1977) promotes channel instability (Burkham 1981; Graf 1988b), and slow rates of
channel recovery (Wolman and Gerson 1978). Desert streams are characterized as
having unstable channels (Burkham 1981; Graf 1988b), yielding abundant sediment
(Langbein and Schumm 1958) that is entrained or stored depending on streamflow
conditions. Flashy discharge caused by localized meteorological events is transmitted
quickly through a terminable portion of the stream system (Burkham 1970).
Streamflow in humid regions, on the other hand, is more regular and often differs little
during higher streamflow events. Channel dimensions are regulated by previous
streamflows (Schumrn 1977) and are determined by sediment load, discharge, and
valley slope (Waters 1992). Because streamflow is regular, channels in humid regions
are more stable than those in dry regions. The regularity of flow that characterizes
humid region streams promotes channel recovery after extreme events (Costa 1974).
Thus, models for channel change that have been developed for perennial streams in
more humid environments are not adequate for explaining the operation of desert
Sediment Characteristics
Exhaustive discussions of the processes of sedimentary deposition and the
characteristics of sediments in alluvial environments have been compiled by numerous
authors (e.g., naming only a few, Boggs 1987; Church 1981; Miall 1978, 1992;
Morisawa 1985; Ritter 1986; Waters 1992) and to prepare another such discussion
would be pointless. However, a quick review of the factors that contribute most
significantly to streamflow reconstruction and depositional environments along the
focus reach will facilitate later discussions of Santa Cruz River stratigraphy.
A number of factors contribute to sediment characteristics, including stream
morphology, depositional regime, and velocity of streamflow. Each of these factors
creates distinct sedimentary structures, facies, and sediment architecture (features
within a deposit), which can be used to recognize the factors that created them (Miall
1992). The current morphology of the focus reach is that of a meandering stream. In
the past, however, it is possible that the stream had a different morphology. In fact,
Waters (1987, 1988) has suggested that the Santa Cruz was a braided stream during
the middle Holocene.
Braided Streams
Braided streams typically contain numerous bars that represent temporary
storage of sediment deposited during periods of reduced streampower. Braided
streams are characterized by highly variable discharge, allowing for storage of
sediment that the stream is incompetent to handle (Leopold and Wolman 1957).
Either lateral or vertical accretion of sediments is possible under a braided stream
regimen; each of these depositional processes creates vertical sequences that reflect
fluctuations in bedload and discharge (Boggs 1987).
Meandering Streams
The typical model for a meandering stream begins with a basal lag deposit of
gravel overlying an erosional surface and is followed by an upwardly-fining sequence,
terminating in fine overbank deposits typically comprised of mud and/or silt (Allen
1970). Sand and gravel in the basal unit typically decrease in size toward the top of
the pile and display trough cross-bedding features'. These features are created by a
complex set of processes related to low-flow and high-flow conditions. During
low-flow conditions, the river hugs the outer (concave) part of the meander, but during
high-flow conditions it takes a straighter path. Lateral shifting of the current causes
the water to circulate in a strong spiral pattern known as helical flow. This type of
flow carries sediment across the stream channel to the inner bank, releasing it under
lower velocity conditions in point bars. Turbulent, high velocity flow along the outer
bank results in deposition of only the coarsest sediments (Boggs 1987). Overbank
flow occurs during flood stage, leaving behind a deposit of fine silt and mud on the
Inferences regarding paleocompetence can be derived from sedimentary
characteristics displayed in prehistoric alluvial sequences. These inferences are based
on a long history of documentation of the processes that create these characteristics. It
is important to recognize that desert streams will operate in a manner unique to
streams in more humid regions; therefore, historical reconstructions of the mechanisms
under which the Santa Cruz operates can provide additional data to be used in
inferential modeling.
Historic records of the Santa Cruz River, compiled predominantly by
Betancourt and Turner (1990), provide examples of the types of flow conditions
possible under channel parameters which do not exist today, but which may have
existed at different times prehistorically. Historic records prior to incision of the Santa
Cruz (see below) consist predominantly of cadastral surveys, newspaper reports,
personal diaries or journals, and photographic records.
For the early part of the historic period, personal diaries and journals and
historic cadastral surveys have provided some of the most detailed descriptions of the
river. Occasionally, these records provide accounts of the vegetation present along the
banks and on the floodplain of the river, the depth and width of the channel, the
presence of water or of waterlogged areas, the agricultural potential of floodplain soils,
the techniques used in agriculture, and the nature of sediments within the channel.
Each of these types of data can be used to infer the flow conditions under certain
channel parameters. For example, the depth and width of the channel, when combined
with accounts of the frequency and extent of flooding, can yield important data about
the nature of sedimentation that potentially occurs under those channel parameters.
Historic records also provide examples of the way in which cause-and-effect
relationships operate to produce channel changes. Historic records of the incision of
the Santa Cruz channel (discussed in greater detail below) have revealed the
multiplicity of factors that caused the Santa Cruz to incise to its present depth and the
reasons for its extensive channel widening (Betancourt and Turner 1990; Parker 1995).
Historic records also provide information about key landscape and hydrologic features
that may repeatedly be the source of threshold changes in certain river systems.
Stable landscape features such as mountains, bedrock features, and other impenetrable
surfaces can act as boundaries to surface and groundwater flow and can influence
hydrologic and sedimentary input into the stream system.
Together with application of the known laws under which rivers operate, these
historic data can be powerful interpretive tools. The following descriptions are used as
a basis for inferring the flow conditions possible under channel parameters
prehistory that are similar to those during the historic period. The following accounts
of the historic Santa Cruz River are derived predominantly from data presented
Betancourt and Turner (1990).
Historic Descriptions of the Santa Cruz River
The Santa Cruz River is a deeply entrenched drainage much like many of the
drainages found in southern Arizona. The river today exhibits steep, nearly vertical
channel walls. However, before the turn of the century, historic accounts and
photographs portray the Tucson portion of the river as a reliable source of water,
shallowly incised, with perennial reaches that supported cottonwood groves and wet
meadows called cienegas. These cienegas were located historically in at least two
places, at the base of A-Mountain and at Punta de Agua, near San Xavier. Historic
accounts of cienegas are supported by the presence of clay-rich sediments exposed in
the stream banks 2 .
These same historic sources also tell us that the Santa Cruz was a chain made
of diverse microenvironmental links. Perennial reaches present in historic accounts
covered only 20 percent of the entire river course. Other reaches of the Santa Cruz
were intermittent and mesquite bosques were present in some parts of the valley.
Although historic cadastral surveys rarely mentioned depth of the channel, short
entrenched reaches were present by 1849 upstream of Tucson and by 1871 near San
By 1882, the discontinuous arroyo near Tucson had incised three meters.
Hydrologic changes related to an earthquake in 1887 created a new arroyo, Spring
Branch, in a cienega near Martinez Hill. Natural processes were exacerbated by
human impacts and by 1890 a combination of ill-designed diversion ditches, a
declining water table, and a series of large floods caused headward erosion (cutting
upstream) to form or deepen these entrenched reaches. Additional winter floods in
1905 and 1915 resulted in the continuously entrenched, only occasionally flooding,
river with which we are familiar today.
Historical records from specific reaches within the valley portray the individual
character of the Santa Cruz throughout parts of the historic period. Though each reach
changed over time, a fact that is highlighted by in-depth examination of historic
records over several years (Betancourt and Turner 1990), the portrayals noted below
have been gleaned from historical records because of their applicability to the study
area and their apparent consistency over time.
San Xavier and Martinez Hill
Perennial flow during the historic period at San Xavier is ascribed to a buried
dyke of flat-lying basalt. This dyke blocks flow into northern reaches of the Santa
Cruz and draws groundwater to the surface. A spring called Punta de Agua is known
from the San Xavier area and is attributed to the development of a cienega in this part
of the river.
As early as 1699, when Father Kino visited San Xavier, the mission was
well-endowed with extensive agricultural fields, supplied by numerous irrigation
ditches. South of San Xavier, these historic accounts describe "plains and meadows
covered with pasture" (Manje 1954 in Betancourt and Turner 1990:43); however, there
were also miles with no perennial flow in this area.
Springs are also reported at Agua de la Mission, near Martinez Hill and are
attributed to yet another cienega. It is this cienega that was cut by the earthquake in
A-Mountain/Sentinel Peak
Historically, groundwater was forced to the surface by an impenetrable
stratum in the narrow part of the valley surrounding A-Mountain (Hinderlider 1913 as
cited in Betancourt and Turner 1990:58). Some historic accounts describe springs near
the base of A-Mountain (Betancourt and Turner 1990:50), though most historic records
place these springs only on the south side of the mountain (Betancourt and Turner
Historic photographs and records indicate that the bottomlands (floodplain)
surrounding Sentinel Peak were about a mile wide and were crossed by "irrigating
canals in every direction" (Bartlett 1854:292-302, as cited in Betancourt and Turner
Focus Reach: Grant Road to Ruthrauff Road
Few historic records are available for the area surrounding the Los Pozos site
during the historic period; however, the accounts that are available portray a river that
was a relatively reliable, though small stream for about 10 mi north of A-Mountain.
The channel was rarely more than 3 m wide and often no more than 1-2 m deep.
Several early accounts suggest that mesquite bosques were present intermittently along
the course of the channel for several miles south of Point of the Mountains. A later
survey places a thick mesquite grove just south of Los Pozos where the river becomes
a narrow channel after occupying an approximately 10 m width.
Rillito Creek
Although not directly part of the focus area, sedimentary input from Rillito
Creek has significant influence on the Santa Cruz River; its historic character is,
therefore, summarized in the following discussion. As the Santa Cruz reaches Rillito
Creek, historic accounts portray it as broadening slightly. Rillito Creek today exhibits
a relatively straight channel pattern with nearly vertical walls. However, historic
records suggest that the Rillito was once a wide, shallow, braided stream:
[In 1858] The entire valley was an unbroken forest, principally of
mesquite, with a good growth of gramma [sic] and other grasses
between the trees. The river course was indefinite, - a continuous grove
of tall cottonwood, ash, willow, and walnut trees with underbrush and
sacaton and galleta grass, and it was further obstructed by beaver dams
(Smith 1910:98).
This account of the Rillito channel has been confirmed by examination
of paleoflood
records, aerial photographs, and survey records (Slezak-Pearthree and Baker 1987).
Changes in land use, a series of large floods, and the incursion of large, obstructive
linear constructions such as roads, diversion dams, canals, and the Southern Pacific
Railroad caused channel changes that occurred near the turn of the century.
As a tributary channel to it, the Rillito responded to historic incision of the
Santa Cruz by adjusting to a new base level. Headward erosion of the Rillito from its
confluence with the Santa Cruz resulted in entrenchment of the Rillito in several
reaches. Though little documentation of these changes is available, historic accounts
of early floods along the Rillito suggest that the Rillito "[flowed] on an upper surface
of alluvial fill [T-2]" (Graf 1984) and that during high-magnitude floods, water rose
over the floodplain. However, by the 1890s, entrenchment and lateral erosion of
channel banks had begun (Hastings 1958). By 1930, entrenchment was complete (U.S.
Army Corps of Engineers 1986). Smith (1910) suggests that entrenchment of the
Rillito and creation of its now nearly vertical banks was caused in part by overgrazing,
cutting of floodplain grasses for hay production, concentration of runoff in cattle trails,
and summer floods. Most of these effects were felt after the U.S. Army post was
moved to Fort Lowell in 1872.
Canada del Oro to Point of the Mountains
Abundant historic survey data has been compiled from the area north of
Cariada del Oro to the northernmost edge of the Tucson Mountains (Point of the
Mountains). Historically, the river was very broad here and exhibited a very shallow
channel, rarely more than 1 m deep. Few other historic accounts are known from the
area, however, and most of these are vague in placement. Tucson is described as "the
lowest line of constant running water" (Emory 1857 in Betancourt and Turner
1990:51) and the river "never succeeds in reaching the Rio Gila" (Bell 1869 in
Betancourt and Turner 1990:56).
Utilizing data from historic period flows along the Santa Cruz River, Parker
(1995) developed a model for channel change along the Santa Cruz River. Although
his purpose was primarily related to predictive modeling of channel change for flood
hazard assessment and planning purposes, he also employed the results of his research
to develop a conceptual model for prehistoric channel changes. Parker employed
geomorphic concepts developed by fluvial geomorphologists over the past 50 years,
and utilized characteristics of the channel, the drainage network, and geomorphic
surfaces in his model.
Channel pattern, dimensions, and aerial photographs were used to reconstruct
the lateral processes involved in channel change. Meteorological events (storms) and
discharge records were used to examine the effects of spatially and temporally variable
precipitation on hydrologic processes of the Santa Cruz River. He concluded that
spatial variability of channel change is controlled by major landscape elements. The
nature of channel change within a single reach is, therefore, predictable.
Parker (1995) has divided the portions of the Santa Cruz River
flowing through
Tucson into three reaches: San Xavier (Pima Mine
Road to 22nd Street/Sentinel
Peak), Tucson (Sentinel Peak to the Rillito River), and Cortaro (Rillito
Cortaro Road). The study area of this dissertation encompasses all
River to
of the Tucson
reach and parts of the Cortaro reach. Results of previous work
in the San Xavier
reach is examined in Chapter 4 as a reference point from which to understand new
research within the study area. The focus area is contained within Parker's (1995)
Tucson reach. Using Parker's (1995) dissertation as a guide, the geologic and
topographic controls that affect channel change within these reaches are reviewed
San Xavier Reach
Previously confined by intramontane basin fill and the Quaternary Jaynes
terrace, the Santa Cruz River enters the San Xavier reach where the basin widens.
Here, floodwater is able to spread widely, depositing large volumes of fine-grained
material. The reach upstream from Pima Mine Road is characterized by high sediment
production and mobility; these large quantities of sediment are delivered to the San
Xavier reach. As a consequence, the San Xavier reach is characterized by sediment
storage, creating cienega conditions and aggrading floodplains with shallowly-incised
or unincised channels. Coarser sediments are transported through the reach during
intermittent periods of discontinuous arroyo formation. Although the reach has
experienced few periods of continuous arroyo entrenchment, only
a fraction of the
stored sediment was removed during these periods.
Tucson Reach
As the river enters Tucson, it is again constricted into a narrow valley, formed
on the west side by alluvial fans emanating from the Tucson Mountains and on the
east by the Jaynes, Cemetery, and University terraces. Because sediments are
south of A-Mountain, the Tucson reach receives little to no sedimentation from
San Xavier reach. Minor sedimentary input is derived from the Tucson Mountains and
from erosion of the Quaternary terraces, contributing a rather coarse sediment load.'
Low sedimentary input, coupled with sediment storage in upstream reaches, can
cause sediment storage in the Tucson reach. Parker characterizes this stored sediment
as "a wedge...[that] moves downstream through the Tucson reach" (Parker 1995:175).
The steep valley slope causes frequent sediment removal at the downstream margin
this wedge. This zone of "sediment evacuation" serves as the threshold point for rare
episodes of continuous arroyo formation extending upstream through the entire San
Xavier reach. Headward erosion during periods of continuous arroyo formation and
subsequent arroyo widening substantially increase sediment delivery to the Tucson and
San Xavier reaches. Because storage space is low in the Tucson reach, the reach acts
as a zone dominated by sediment transport.
Cortaro Reach
At the Cortaro reach, the valley widens again and is bounded by alluvial fan
sediments, derived on the west from the Tucson Mountains and on the east and north
from the Santa Catalina Mountains.
The resemblance [to the San Xavier reach] does not extend to channel
morphology and the nature of channel change, however, because of
differences in sediment source and hydrologic differences that are at
least partly related to landscape controls. The proximity of the Cortaro
reach to significant sediments sources, particularly the piedmont of the
Catalina Mountains and the upper watersheds of Taupe Verde Creek
and Pantano Wash result in high sediment delivery rates (Parker
Channel widening, shifting channel positions, and frequent, low-magnitude changes in
channel elevation are caused by a combination of increased discharge and coarser
sediments in this reach. High rates of lateral erosion result in short sediment storage
times, but high sediment input have made the Cortaro reach one of long-term
aggradation. As a result, "the residence times of sediments stored more than a few
meters below the flood plain is relatively high" (Parker 1995:176). Downstream of the
Cortaro reach, the river becomes completely unconfined, eventually emptying into the
area known as the Santa Cruz Flats.
Parker (1995) does not address the effects of short-term sediment storage and
gentler valley slope in the Cortaro reach on the upstream Tucson reach. Changes in
sediment delivery, sediment storage, and valley slope within the Cortaro reach should
have significant effects on the Tucson reach. Because flood flows on the southern
portion of the Santa Catalina Mountains are significantly affected by the frequency,
size, and type of storms (Martinez-Goytre 1993; Martinez Goytre et
al. 1994), the
interaction of climatological processes and hydrologic response within the
reach would have played a key role in the removal or storage of sediments
in the
Tucson (focus) reach. According to Parker (1995), tropical and frontal
storms produce
the kind of intensity and extent to cumulate energy in downstream reaches.
Utilizing both regimen-based reconstruction and paleocompetence
reconstruction as a guide, Parker (1995) suggests that prehistoric periods of channel
filling were the result of sustained periods of low to moderate discharge during which
tropical and frontal storms would not occur or would occur with lower frequency than
the present. In the absence of scouring floods created by these storm types, sediment
is removed from or entrained through reaches of long-term sediment storage by
shallowly-incised, meandering channels or through the incision and excavation of
discontinuous arroyos. Parker (1995) cites Waters' (1988) units V 2 and V 3 , as
examples of such channel filling episodes. Parker (1995) further contends that such
periods would be dominated by monsoon-caused flood, incapable of producing storms
of a magnitude or frequency to sustain or intensify streampower in downstream
reaches. Monsoonal storms may, however, have an effect on smaller tributary basins.
Parker (1995) also suggests that continuous and deep channel entrenchment
produced by tropical and frontal storms would have been dependent on the character
of the pre-entrenchment channel. Discontinuous, entrenched reaches would have been
impacted by tropical and frontal storms to a greater effect than indistinct, unincised
channels in vegetated cienega environments. Under the right pre-entrenchment
conditions, these discontinuous, entrenched reaches would have coalesced into a single
continuously entrenched channel.
It is important to recognize that neither Waters (1988) nor Parker (1995) were
equipped with prehistoric records from the Tucson reach to use as a guide for
reconstruction of the prehistoric behavior of the Santa Cruz River. Chapters 4, 5, and
6 (below) describe the prehistoric record in this reach as a to test of Parker's (1995)
model on that prehistoric record and an explanation for the processes that might have
created the record documented for the focus reach.
1. Variations from the fining-upward model do exist (cf., Collinson 1978); therefore,
this model should only be used as an ideal and not the rule.
2. It must be noted that clay-rich sediments, in and of themselves, are not necessarily
indicative of cienega conditions. This term has been misused in much of the
archaeological literature for the Santa Cruz River. Bruce Huckell (pers. comm., 1995)
has suggested that cienega soils would likely display a mollic epipedon, rather than a
histic epipedon, probably indicating hydrophytic plant growth. These soils appear to
be richer in organic matter than other alluvial deposits. Other characteristics of note
appear to be the thickness of the deposit and the presence of a permeable underlying
layer in which evidence for perennial distribution of water is often found.
3. Parker (1995) attributes the coarse sediment load to short transport distance and
coarseness of the source material.
Today the Santa Cruz River and Rillito Creek are deeply incised, ephemeral
streams. The Santa Cruz originates just north of the U.S.-Mexico border in the Canelo
Hills, running south to Santa Cruz Sonora before turning north and re-entering Arizona
east of Nogales. The reach of the middle Santa Cruz encompassing the
project area is
influenced predominantly by large and small drainages originating in the Tucson
Mountains, the Santa Catalina Mountains, and on the surrounding bajada surfaces.
Rillito Creek, which is a tributary to the Santa Cruz, is served by a series of large and
small drainages originating predominantly in the Santa Catalina and Rincon mountains
and farther upstream by Pantano Wash, Cienega Creek, and other drainages originating
in the Santa Rita, Whetstone, and Empire mountains. As a rule, the differing sources
deliver distinct materials to the streams.
In addition to drainage contribution, the surrounding mountains and terrace
surfaces can affect the hydrologic system of the Santa Cruz in other ways. Small
volcanic hills such as Sentinel Peak and Martinez Hill, along with impenetrable
petrocalcic horizons in surrounding terraces, often act as a barrier to surface flow and
occasionally force groundwater to the surface. The mountains also can have an effect
on atmospheric processes, favoring precipitation in some drainages, rather than others
(Martinez-Goytre 1993).
As outlined in the previous chapter, the current character of the Santa Cruz
River is not indicative of its past historic status. During the prehistoric period, the
Santa Cruz was a dynamic stream system, at times entrenched and other times certain
reaches would flow perennially. Where not covered by soil cement, sections exposed
in the walls of today's arroyo provide access to this prehistoric record. Geologists and
archaeologists examining the walls of the present arroyo and excavating trenches in
the floodplain have described pieces of this record in reaches extending from an area
south of the San Xavier reservation to Ina Road north of Tucson's city center. The
purpose of this chapter is to describe previous and current research in each of these
reaches (excepting the focus reach) as a background for the present study, in order to
synthesize work conducted over 30 years by several scholars.
Using a combination of aerial photometric mapping and field reconnaissance,
the Arizona Geologic Survey mapped the geology of the entire Tucson metropolitan
area (Jackson 1989; McKittrick 1988; Pearthree et al. 1988). They defined five
Quaternary terraces of the Santa Cruz River (Qt 1 through Qt5). Throughout this
chapter, the Arizona Geological Survey's units are referred to in locational maps and
in geological referencing of site areas. Four of these terraces were first described in
the early twentieth century by Smith (1938) and have been correlated with the surfaces
defined by the Arizona Geologic Survey and with sedimentary units identified by
Haynes and Huckell (1986, see below). Table 4.1, below, shows the relationship
between geologic units described by different researchers.
Table 4.1.
Correlation between geologic units defined by different researchers.
Smith (1938)
McKittrick (1988)
Haynes and Huckell (1986)
Qt1 and Qt2
A3 through D
Jaynes terrace
Cemetery terrace
University terrace
Qt5 and Qt4 (the University and Cemetery terraces)
The thick petrocalcic horizon (a layer of hard "caliche," calcium carbonate)
capping the oldest and highest terrace (Qt5 or University terrace), suggests an early to
middle Pleistocene age (Anderson 1987). Soils forming the upper surface of the next
lower terrace (Qt4 or Cemetary terrace) exhibit a well developed clay horizon and
varying degrees of carbonate accretion, indicating that deposition terminated sometime
during the middle Pleistocene. Except where buried by more recent deposits, the
Cemetery (Qt4) and University (Qt5) terraces are of little concern archaeologically.
These terraces were deposited during the middle Pleistocene or earlier. To date, no
archaeological material has been discovered in North or South America that predates
the late Pleistocene.
Qt3 (the Jaynes terrace)
The third terrace (Qt3 or Jaynes terrace) is preserved in only a few places. A
radiometric date on groundwater-derived carbonates from a zone 2.5 m below the
Jaynes terrace surface yielded a minimum age estimate 18,400 B.P. (late Pleistocene)
for the beginning of deposition (Haynes and Huckell 1986). Because the Jaynes
terrace has a complex history that is not fully understood, it is not clear if it could
contain archaeological deposits that are contemporaneous with its formation. Although
this terrace has been identified in numerous reaches of the Santa Cruz River (Haynes
and Huckell 1986, Jackson 1989, McKittrick 1988), the Jaynes terrace remains poorly
defined. McKittrick (1988) and Jackson (1989) defined the surface of Qt3 as
comprised, in part, of moderately to weakly developed argillic (clay) horizons, which
often indicate Pleistocene age. However, Haynes and Huckell (1986) suggest that, in
places, this terrace is buried by younger deposits of the Santa Cruz River, and that it
merges with a lower terrace (Qt2), thereby forming a compound terrace. Therefore,
sediments of post-Pleistocene age can be found on terraces mapped as Qt3; these
sediments can potentially preserve subsurface cultural materials. Nevertheless, the
Pleistocene terrace was probably completely abandoned by 8,000 years ago (cf.,
Waters 1987, 1988).
Qt2 (the Holocene terrace)
The next lowest terrace (Qt2 or Smith's [1938] "bottomlands") is comprised of
unconsolidated sediments of Holocene age, between at least 8000 and 100 years old'.
These sediments demonstrate that the Santa Cruz experienced at least five major
periods of deposition and four downcutting episodes during the last 5,000 years.
These alluvial cycles are bracketed in time by estimated ages on buried archaeological
remains and on the development of calcic horizons, and are further supported by 71
radiocarbon-dates from organic materials incorporated into the sediments (Haynes and
Huckell 1986). In his study of alluvial strata exposed in the arroyo wall south of
Martinez Hill, near the San Xavier Mission, Waters (1987, 1988) extended the range
of this alluvial sequence by at least 2,000 years and refined the chronology with an
additional 27 radiocarbon dates, eight archaeomagnetic dates, and temporally
diagnostic pottery sherds.
Pre-8000 B.P. deposits along the San Xavier reach of the river consist of a unit
of channel gravel. Deposition of this gravel is followed by a lengthy period of
channel erosion and widening between 8000 and 5000 B.P. and later by valley
aggradation between 5500 and 2500 B.P. This aggradational episode is followed by
four epicycles of cutting and filling occurring during the last 2,500 years in this part
of the valley (Waters 1987, 1988). The oldest and deepest Holocene fill identified
north of Martinez Hill is comprised of slope wash deposits (Waters 1987, 1988),
yielding radiocarbon dates between 4800 and 3900 B.P. and containing Middle
Archaic artifacts, isolated features, and archaeological sites (Haynes and Huckell
1986). A weakly developed paleosol caps the alluvial deposit overlying this unit and
has yielded radiocarbon dates from about 3700 to 2600 B.P. Buried Middle and Late
Archaic artifacts and features have also been found on, or excavated into, the top of
this unit. Non-diagnostic lithic artifacts and a hearth have been found within the next
higher fill, comprised of alluvial silts and sands and separated by three or more bands
of clayey sediments. Radiocarbon dates within this unit range from 2500 to 2000 B.P.
Fluvial sands, separated by bands of clay form the next alluvial unit. Late Archaic
hearths and occupational horizons found within this unit probably represent artifacts
redeposited from older surfaces. Colonial and Sedentary period Hohokam ceramics
and habitation sites found within the upper portion of this unit have yielded
radiocarbon ages between 1800 and 1000 B.P. (ca. AD 225-1100). Sedentary and early
Classic period sites are found on the surface of sand dunes, and are partly covered by
alluvial overbank deposits. These alluvial deposits are also found in a floodplain
facies, capped by a weak soil, and containing Sedentary and Classic period
archaeological resources. Radiocarbon dates on these deposits range from 1000 to 190
B.P. (ca. AD 1100-1760). This fill potentially contains protohistoric resources, which
can be difficult to segregate from the earliest ceramic period and historic period
Qtl (the Historic terrace)
More than a meter of mud containing recent trash has been deposited on the
pre-twentieth century terrace by the most recent overbank floods in 1977 and 1983
(Mabry 1993; Freeman 1995, unpublished field notes). A 2- to 3-meter high terrace of
slackwater flood deposits also formed in the mouths of tributary arroyos along the
Tucson reach of the river during these floods, where mud and gravel were spread
across the wide, active floodplain near Marana. Qt1 represents this youngest and most
recent floodplain activity along the Santa Cruz River. Often this terrace is buried or
otherwise modified by historic and modern activities such as mining and dumping. It
is rarely identified along the Tucson reach of the Santa Cruz River.
Since its turn-of-the-century entrenchment, the channel of the Santa Cruz has
reached a gradient on a more resistant bed or on older tougher sediments, limiting the
potential for further downcutting. Channel erosion is now more lateral than vertical.
For this reason, cement-stabilization of the banks is being implemented. During
extreme flood events, which may be associated with an intensification in monsoonal
precipitation, the Santa Cruz River overflows and erodes its banks, creating a
hydrological planning nightmare.
Beginning in the late 1960s and continuing through the late 1970s and late
1980s, Vance Haynes and students from his classes at the University of Arizona began
mapping alluvium exposed in several arroyos between Pima Mine Road and the
Hughes Access Road (south of Martinez Hill). They also mapped exposures north of
Martinez Hill at the San Xavier gravel pit, at the Airport Wash and in Avra Valley.
Together with Bruce Huckell (then at the Arizona State Museum), Haynes had the
opportunity to map exposures of archaeological features and artifacts along Ina Road.
Haynes and Huckell (1986) identified five major (Units A-E) and nine minor episodes
(A 2 through E) of sedimentation from the late Pleistocene through the historic period.
During the late 1980s, Stafford (1986) and Waters (1987, 1988) conducted
geologic investigations of the San Xavier reach of the Santa Cruz River in conjunction
with archaeological research in the private sector. Waters' (1987, 1988) reports of the
reach between Pima Mine Road and Martinez Hill are to date the most inclusive
discussions of these radiocarbon dated units. He identifies seven major geologic units
within this reach (units I through VII). However, because many of the reaches,
described hereafter, will refer primarily to the report by Haynes and Huckell (1986), I
have included their units in parentheses following the Waters' (1987, 1988) unit
Unit I
Unit I (unidentified by Haynes and Huckell) is comprised of sands and gravels,
overlain by a black "cienega" clay, on which pedogenesis has taken place. A
radiocarbon date from the upper portion of Unit lb gave an age estimate of 7970 ±
130 B.P. (Beta 14537) run on organic carbon extracted from the clay. This is the
earliest age on Holocene sediments within the Santa Cruz Valley.
Unit II
Unit II (Haynes and Huckell unit B 2 ), which unconformably overlies this black
clay, is distinctly younger. Charcoal from a hearth in the upper portion of Unit II
yielded a corrected age estimate of 2570 ± 210 B.P. (Beta 13707). The hiatus that
follows deposition of Unit I appears to be relatively continuous across the valley;
however, older dates recovered by Haynes and Huckell (1986) indicate that deposition
of this unit probably began as early as 4000 B.P. In the Brickyard Arroyo, Haynes
and Huckell (1986) also identified a unit near the floodplain margin that appeared to
have been derived from slopewash from the nearby bajada (Waters' unit IIsw, Haynes
and Huckell unit B 1 ). Radiocarbon dates on these sediments have yielded ages
ranging from 5500 to 4500 years B.P. The section from San Xavier is missing this
Middle Holocene unit, that is well-preserved in downstream reaches.
Unit III
Unit III (Haynes and Huckell 1986, unit C 1 ), a series of sands, gravels and silts
follows deposition of a second (brown) "cienega" clay (Unit IIc). Dates on this unit
range from approximately 2400 to 1900 B.P.
Unit IV
Unit IV (Haynes and Huckell 1986, unit C 2 ) consists of channel fill and is
comprised of sand and silty sand with discontinuous silt and clay lenses (Haynes and
Huckell 1986; Waters 1987). Radiocarbon dates on this unit range from
approximately 1800 to 1000 B.P.
Unit V
Unit V (Haynes and Huckell 1986, unit C 3 ) appears to be comprised of
overbank and/or slackwater sediments (predominantly silts and clays), although
Stafford (1986) has identified a channel component of this unit. Radiocarbon dates on
this unit range from approximately 900 to 600 B.P. Unit C 3 is also underlain by a
series of vegetated dunes in a portion of the valley (Haynes and Huckell 1986).
Unit VI
Unit VI (Haynes and Huckell 1986, units C 3 and D) are comprised of channel
fill and overbank deposits of Unit C 3 and modern silty clay and sandy clay overbank
deposits of Haynes and Huckell's unit D. Radiocarbon dates on the older component
range from roughly 450 to 190 B.P. and the younger dates are essentially modern in
Unit VII
Unit VII (Haynes and Huckell unit E) is described by Waters (1987) as modern
clay and silt overbank deposition following historic entrenchment of the Santa Cruz
River. The radiocarbon content of charcoal found within this deposit yields very
young age estimates or exceeds the modern value. Radiocarbon values in excess of
100 percent modern are due to an increase in atmospheric radiocarbon produced by
nuclear testing (Cain and Suess 1976).
The Rio Nuevo South property is located south of Congress Street and west of
the Santa Cruz River within a highly urbanized portion of the Tucson Basin. The
property crosses a series of deposits representing former channels, terraces, and
floodplains of the Santa Cruz River. Here, the Santa Cruz River is diverted around
the Sentinel Peak-Tumamoc Hill volcanic complex, a series of low hills comprised
primarily of basaltic andesites, porphyrys, tuffs, and lavas laid down during the
Miocene and Oligocene. Tumamoc Hill and Sentinel Peak (A-Mountain) were
uplifted, faulted, and tilted southeastward sometime after 20 million years ago (Mayo
et al. 1968; Phillips 1976). Today, both the hills and the river provide important
sources for sedimentary input into the project area. The floodplain and former channel
of the Santa Cruz River are well preserved here due to the presence of Sentinel Peak,
a setting which provides protection of the west bank from high-velocity flows.
Archaeological resources found on the Rio Nuevo South property include a
system of historic and prehistoric canals at the base of A-Mountain (the A-Mountain
Canal System, AZ BB:13:481, ASM) and a series of historic and prehistoric
components including the Tucson Pressed Brick Company and the Clearwater site (AZ
BB:13:6, ASM). The prehistoric component on the Rio Nuevo South property is
referred to as the Clearwater site. This site name, proposed by Doelle (1996) also
encompasses prehistoric components found on Spruce Street and Brickyard Lane,
formerly known as the Brickyard site (Smiley et al. 1953).
Clearwater Site (AZ BB:13:6)
The highest density of prehistoric archaeological resources on the Rio Nuevo
South property is represented by an Early Agricultural period component, located in
the southern portion of the Rio Nuevo South property, south of Congress Street and
west of the river (Diehl 1996b). Another relatively high density of features is located
along Brickyard Lane, south of the Rio Nuevo property (Elson and Doelle 1987). A
few isolated features have been found in trenches along Spruce Street (Diehl 1996b).
The area encompassed by these features suggests that the Clearwater site is quite large,
however few individual features have been excavated. Because the area excavated is
relatively small, it is difficult to determine whether the individual loci forming the
defined Clearwater site is one large site or a series of smaller sites.
Because the geologic investigations described below were conducted only in
conjunction with the portion of the Clearwater site located on the Rio Nuevo property,
the results of those investigations are presented here. Earlier investigations also
identified Early Agricultural period pit structures (Elson and Doelle 1987; Smiley et
al. 1953).
Testing was conducted on the Rio Nuevo property in spring and fall 1995
(Diehl 1996a; Thiel 1995a, 1995b). A portion of this testing was conducted because a
storm drain, following the alignment of Spruce Street to the southern portion of the
Rio Nuevo property was to be installed. Excavation of Early Agricultural features in
the southern portion of the property was conducted as part of that storm drain project.
Two pit structures, thirteen extramural pits, a trash midden, and a single, flexed
human burial were excavated within floodplain sediments comprising a narrow strip of
land in the southern portion of the Rio Nuevo property (see below). The storm drain
right-of-way cuts through most of that narrow strip of land. The Early Agricultural
settlement potentially covers a roughly 7500 sq m area. Only a portion of this area
was excavated. Buildings and other features related to operation of the Tucson
Pressed Brick Company directly overlie most of the Early Agricultural features,
removing or disturbing any prehistoric sediments that may have postdated the Early
Agricultural period features; some Hohokam artifacts were found in overlying the
Early Agricultural features.
Both pits and pit structures were filled with trash containing animal bone,
flaked and ground stone, and the remains of plants, including maize. Radiocarbon
dates on annuals found in these features are presented in Table 4.2. These dates
produced an average age estimate of 2471 ± 16 B.P. The date corresponds well with
the presence of Cienega (n=12), San Pedro (n=2) and Cortaro (n=2) projectile points
found at the site. The date also places the site on the earlier part of the Cienega phase
and roughly contemporaneous with the Wetlands site (AZ AA: 12:90), described later
is this chapter.
On the basis of plant ubiquities, Diehl (1996b) suggests that maize farming,
small seed harvesting, and cactus fruit harvesting all played a role in the economy of
these early inhabitants. Seasonality was not addressed in the site report. The
Clearwater site also had a smaller, but more diverse faunal assemblage, but like at
many of the Early Agricultural period sites in the floodplain appeared to be focused on
lagomorphs and artiodactyls. The site also contained Cienega phase pottery.
Table 4.2
AMS radiocarbon dates from A-Mountain mitigation features.
Calibrated Age
Age (B.P.) b(1 S.D.)
Calibrated Age
(2 S.D.)
2580 ± 60
2500 ± 60
805 - 770 B.C.
785 - 505 B.C.
825 - 525 B.C.
800 - 405 BC,.
Maize cupule
2600 ± 50
2390 ± 50
810 - 780 B.C.
505 - 395 B.C.
825 - 560 B.C.
760 - 380 B.C.
Maize cupule
2420 ± 50
745 - 400 B.C.
770 - 390 B.C.
780 - 515 B.C.
380 - 205 B.C.
795 - 410 B.C.
Sample a
Maize cupule
Maize cupule
insufficient carbon to obtain date
Prosopis seed
2500 ± 50
Prosopis seed
Prosopis seed
2250 ± 50
2390 ± 70
Prosopis seed
Maize cupule
2440 ± 60
525 - 390 B.C.
760 - 405 B.C.
395 - 180 B.C.
775 - 365 B.C.
785 - 390 B.C.
Prosopis seed
2430 ± 60
2510 ± 50
760 - 400 B.C.
785 - 525 B.C.
780 - 385 B.C.
800 - 415 B.C.
Prosopis seed
2440 ± 60
760 - 405 B.C.
785 - 390 B.C.
Prosopis seed
2480 ± 50
775 - 425 B.C.
2471 ± 16
760 - 415 B.C.
790 - 405 B.C.
765 - 410 B.C.
a Piii
samples are from Beta-Analytic, Inc.
Corrected using the C13/C12 ratio; in years before present.
`Calculated mean excludes sample B-90232.
S.D. = standard deviation
On the basis of a high proportion of bifaces at the site, Sliva (in Diehl 1996b)
suggests that the site represents a short-term camp associated with a high-degree of
residential mobility. The assemblage pattern runs counter to other analyses, including
the high ubiquity of maize in feature contexts, and also runs counter to other Early
Agricultural period assemblages. For this reason, Sliva suggests the possibility that
the tool-type patterning reflected in the site assemblage may represent a task-specific
function. Given the small proportion of site excavated, its presence on the outer edge
of the known boundaries of the Clearwater site, and the relatively few number of
features excavated, assemblage bias must be considered a possibility.
Project Area Background
The Rio Nuevo south property is located in an area mapped by the Arizona
Geologic Survey as representing Qt2 (Figure 4.1). This terrace represents a complex
suite of geologic events and encompasses a large part of the Holocene epoch (postPleistocene) in which most of the evidence for prehistoric occupation of the Santa
Cruz Valley is found. Further confounding the geology of the project area is that the
Sentinel Peak-Tumamoc Hill complex, in protecting sedimentary deposition along the
western side of the Santa Cruz River, has preserved sediments and promoted the
development of soils not likely to be found elsewhere along the Santa Cruz River.
The geomorphology of the project area and its deposits has been previously
studied by Ahlstrom et al. (1994) and Katzer (1987). Because Katzer's (1987)
examination of the project area was limited to a few widely dispersed trenches, he was
able to identify only one of the five geomorphic units described in this report.
Ahlstrom et al. (1994) were similarly limited by the scope of their project, but they
were able to identify what are essentially included in the following section as
allostratigraphic Units 2, 3, 4, and 5 (though Units 3 and 5 were lumped as a single
3565000m fki
3563000m N
Figure 4.1. Location of Clearwater site showing surficial geologic deposits and relevant Rio Nuevo
and Alameda Street cross-sections, A-A', B B', and C-C'. UTM coordinates indicate the position of map
on the USGS 7.5 topographic quadrangle, Tucson, AZ.
unit defined only as "channel deposits"). The fifth unit described in this chapter,
allostratigraphic Unit 1, is critical to the identification and evaluation of the prehistoric
component on the property and is temporally and geomorphically separate from later
The geomorphic units defined in this report (allostratigraphic units 1-5) were
summarily covered in the report and the data recovery plan for testing on the Rio
Nuevo South property (Diehl and Freeman 1996). Unit boundaries are defined on the
basis of their geomorphological origin and associated ages in order to provide a model
for recovery of archaeological resources on the property. The following discussion of
these allostratigraphic units utilizes data recovered during all phases of archaeological
research as well as data from previous reports (Ahlstrom et al. 1994; Katzer 1987), to
elaborate on the relationships between these units.
Backhoe trenches excavated for archaeological testing were utilized to define
the relationships between geologically distinct units. When unique geologic features
were exposed, trenches were extended deeper, where necessary, to better define the
boundaries between stratigraphically distinct geologic units. The relationships between
distinct stratigraphic and geomorphic units were identified and recorded using a
modified adaptation of the USDA and Folk classification systems (Folk 1954, 1974;
Soil Survey Staff 1951, 1975). A 4.5-m-deep stratigraphic trench was also excavated
to examine the relationship between prehistoric channels of the Santa Cruz River and
project area features, including a historic canal. The location of trench profiles, soil
profiles, and the stratigraphic pit (referred to in descriptions below) are shown in
Figure 4.2.
The project area is generally defined by five distinct episodes of sedimentation
and soil formation: Unit 1, an early series of alluvial deposits, is truncated by Unit 2,
a younger series of alluvial deposits, the upper portion of which forms what has been
previously called a "cienega." These two deposits are likely followed by an incision
(as yet obscured by modern mining and dumping) and deposition of Unit 3, a
sequence of younger alluvial sediments, including a prehistoric channel of the Santa
Cruz River, and Unit 5, a second channel. The surface distribution of these deposits is
represented in Figure 4.2. The project area is covered in places by dumping and
potentially by historic channels created when diversion ditches were further eroded by
natural processes (Unit 4).
Allostratigraphic Unit 1: Early Agricultural Period Floodplain Alluvium
Unit 1 is comprised of a series of alluvial deposits consisting primarily of tan
silts and very fine sands interrupted by thick, dark brown, silty clay to clay bands
(Figure 4.3, units I-V; Figure 4.4, unit I). These fine-grained deposits are the result of
slow deposition of overbank or slackwater sediments on the floodplain of the Santa
Cruz River. Three strongly developed paleosols and two weakly developed paleosols
UNIT 3 -.'%
A—Mountain Testing
Stratigraphic Pit
Tri —Tr7
Desert Archaeology backhoe trenches
San Agustin Project (1986)
Desert Archaeology backhoe trench
A—Mountain Testing Project (1995)
Rio Nuevo South Testing Project (1995)
trench datum
Early Agricultural Period
floodplain deposits
Agua Caliente Phase
and later clenega deposits
Rincon Phase and later channel
deposits of the Santa Cruz River
deposits modified or created by
historic or modern processes
prehistoric or historic channel margin
deposits of the Santa Cruz River
100 m
500 ft
Digital cartography by
GEO-MAP . Inc. 1997
Figure 4.2 Location of allostratigraphic units identified at the Clearwater site and relevant trench
locations referred to in text.
(.76 m1
.09 m
"'Datum 112.04
-.22 m
.30 m
• •
. • •
O ui
. . . •
-.30 m
• • .
• . •
• • • •
Unit II: Dark grayish brown, silty clay loam. Strongly
effervescent. Numerous fine carbonate filaments
distributed throughout this unit. Fine, subangular blocky
peds. Upper contact is abrupt and flat. Erosional
disconformity is present between units II and III.
Unit III: Brown, loamy sand (Ma), grading upward to
a sandy silt (111b). Structure is medium to fine,
subangular blocky (IIIb) to massive in the lower portions
of the unit (IIIa). Effervescence is strong in the upper
portions of the unit (IIIb), moderate in the center of the
unit, and non-effervescent in the lower portion of the
unit (1Ila). Many fine carbonate filaments are present in
the upper portion of the unit. The upper contact is
abrupt to clear and flat. Erosional disconformity is
present between units II and III. Soil development is
moderate at this contact.
Unit IV: Brown, massive fine sand (IVa) grading
upward to a dark grayish brown to very dark grayish
brown, silty clay loam (IVb). Some horizontal bedding
still present in unit IVa. Very fine, subangular blocky
structure in upper portion of unit (IVb). Effervescence
is strong (IVb) to moderate (IVa). Moderate soil
development represented by the presence of some fine
carbonate filaments. Upper contact is clear, flat, and
- Bottom of conformable.
trench (-233m)
Unit V: Dark grayish brown to brown massive silt (Va)
to grayish brown loam (Vb) with very fine, subangular,
blocky structure. Effervescence is strong to moderate.
Some fine carbonate filaments are present throughout the
unit. Upper contact is clear, flat, and conformable.
Unit I: Brown, coarse sand grading upward to fine,
sandy clay loam (la), fining upward to a brown, silty
clay loam (lb). Diffuse pedogenic boundary between la
and lb. Effervescence is strong (lb) to moderate (la).
Many fine carbonate filaments are found in upper
portion of the unit (lb). Some evidence of pedogenic
reworking (clods of sediment from unit II distributed in
upper unit I) between units II and I. Incipient soil
formation in the upper portion of unit I is somewhat
masked by soil development from unit II; the upper
contact represents a compound soil. Upper boundary is
flat, clear, and appears conformable. Feature 365
appears to be excavated from the top of this unit.
1.37 m
Figure 4.3. Stratigraphic column, south wall of
Trench 112.
Unit VI: Grayish brown, massive sandy loam.
Moderately effervescent. Upper surface is disturbed by
modern activities.
Unit 1
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are formed within these dark clay bands. Pithouses that date to the Early Agricultural
period are found within the upper three paleosols (Figure 4.3, units IIIb, IVb, and Vb).
Other cultural materials found within the upper portion of this unit include a Cienega
phase (800 B.0 - A.D. 150) projectile point and Agua Caliente (A.D. 150 - 550) phase
sherds. A radiocarbon date on charcoal from the Early Agricultural period occupation
of 2520 ± 40 B.P. (Beta 85405) fits with the expected date for the Cienega phase
projectile point and provides a minimum age for the upper portion of Unit 1. An
additional 13 radiocarbon age estimates were run on charcoal from archaeological
features within this deposit (Beta 90225-90232, 90230 excluded, and Beta
92617-92622). These dates produced an average age estimate for the prehistoric
occupation of Unit 1 of 2471 ± 16 B.P. (see Table 4.2). Historic features related to
the Tucson Pressed Brick Company overlie the Early Agricultural period pit features.
No radiocarbon estimates have been run on charcoal recovered from Feature 365,
located in the lowermost paleosol identified on the property.
A significant hiatus marked by a disconformity follows deposition of the
sediment on which the Early Agricultural paleosol is formed and deposition of Unit 2
to the west and north. It is possible that the Early Agricultural period occupation of
Unit 1 (and paleosol formation) is concurrent with the initial deposition of cienega
sediments within the area marked Unit 2. Unit 1 is truncated on the east side by an
erosional unconformity that may be related to channel incision following the Early
Agricultural occupation at sites downstream from the project area (Freeman 1997;
Huckell 1996a). Erosion of this paleochannel is followed by deposition of Unit 3
(Figure 4.4, Units II and III).
Allostratigraphic Unit 2: Early Agricultural to Historic Period Cienega
Unit 2 is a series of younger alluvial deposits located across the majority of the
parcel. The lowest-recognized unit of this deposit is a medium to coarse sand and fine
gravel. This sand and gravel is overlain by a very thick (in places, exceeding 1.5 m
depth), dark brown, silty clay deposit, which has been described previously as a
cienega (Ahlstrom et al. 1994; Katzer 1987). This deposit is generally 1.5 to 2 m
thick, and sedimentation throughout the deposit is continuous and uninterrupted.
Katzer (1987) examined seven trenches on the Rio Nuevo South property (Figure 4.2,
tri through tr7). He identified this unit as extending south to the portion of the
Clearwater site excavated by Elson and Doelle (1987) near Brickyard Lane. His
profile (Figure 4.5) demonstrates the variability in the thickness of this deposit over
the length of those seven trenches and 11 additional trenches along Brickyard Lane.
Both the cienega and underlying sand and gravel are considered part of Unit 2.
The upper surface of Unit 2 has been modified significantly by historic
plowing. However, the structure of the soil formed within, the thickness of the
deposit, and indications of significant groundwater seepage in the form of upwelling
features and oxidized mineral deposits at the boundary between the dark brown silty
clay and the underlying sand and gravel suggest that this deposit would support the
growth of wetland grasses, sedges, and other plants (cf. Hendrickson and Minckley
1984). The presence of a cienega in this area is known from historic accounts
(Betancourt and Turner 1990), but most accounts place the cienega south of Sentinel
Peak. It is possible that groundwater availability and protection of the area from
erosion, or the presence of additional spring seeps, allowed a similar feature to extend
north of Sentinel Peak. The bedrock outcrop formed by Sentinel Peak may have even
promoted sediment accumulation downstream of this source area that would not be
eroded by natural alluvial processes.
Congress Street
Mission Lone
--,Y V P
p e i t,_iv
Cress-Section of Cien ego
4 ,11
Medium-to-Coarse Sand and Fine Gravel
2 Figure 4.5
70:1)0 Meters
Profile of trenched area showing a north-to-south cross-section of the alluvial
soils (from Elson and Doelle 1987). Both Cienega and underlying sand and
gravel are considered part of allostratigraphic unit 2.
Archaeological materials located Unit 2 postdate the Early Agricultural period
pithouse occupation, with the exception of a single Cortaro point from a disturbed
context. Canada del Oro phase ceramics and some Agua Caliente phase ceramics are
found in features within the cienega-like sediments in the upper portion of Unit 2.
These archaeological materials suggest a minimum date for Unit 2 sediments of at
least A.D. 750 to 850 and possibly earlier (A.D. 150 - 550, based on dates for the
Agua Caliente phase). Historic Papago plainware ceramics are also found in the
upper portion of Unit 2. A canal (Canal B, not shown on figures) crosses Unit 2 and
Unit 1. On the basis of geometry and placement, the canal is probably prehistoric, and
likely dates to Hohokam Colonial or later periods.
Allostratigraphic Unit 3: Pre-Rincon Period Alluvium
Unit 3 is a series of young alluvial deposits representing a prehistoric channel
of the Santa Cruz River postdating Unit 1, and which also appears to postdate Unit 2.
The relationship between this deposit and older sedimentary units has been obscured
by historic and modern modification of the ground surface that prevents examination
of the contact between these units. An erosional contact between Unit 1 and what is
probably Unit 3 was recognized in trench 12 (Figure 4.4). The cross-section for
trench 12 is marked on Figure 4.1 as B-B'. The fill of that erosional contact is
marked here by a package of silts and clays (Units II and III) representing a sequence
of overbank and floodplain deposits. Clay deposits within this package of sediments
are thickly developed and may form a facies relationship with Unit 2. Occasional
fire-cracked rocks are found within the upper portion of this deposit, probably
representing the sedimentary reworking of prehistoric Early Agricultural deposits. The
portion of Unit 3 identified in the stratigraphic pit Figure 4.6 represents bank margin
least A.D. 750 to 850 and possibly earlier (A.D. 150 - 550, based on dates for the
Agua Caliente phase). Historic Papago plainware ceramics are also found in the
upper portion of Unit 2. A canal (Canal B, not shown on figures) crosses Unit 2 and
Unit 1. On the basis of geometry and placement, the canal is probably prehistoric, and
likely dates to Hohokam Colonial or later periods.
Allostratigraphic Unit 3: Pre-Rincon Period Alluvium
Unit 3 is a series of young alluvial deposits representing a prehistoric channel
of the Santa Cruz River postdating Unit 1, and which also appears to postdate Unit 2.
The relationship between this deposit and older sedimentary units has been obscured
by historic and modern modification of the ground surface that prevents examination
of the contact between these units. An erosional contact between Unit 1 and what is
probably Unit 3 was recognized in trench 12 (Figure 4.4). The cross-section for
trench 12 is marked on Figure 4.1 as B-B'. The fill of that erosional contact is
marked here by a package of silts and clays (Units II and III) representing a sequence
of overbank and floodplain deposits. Clay deposits within this package of sediments
are thickly developed and may form a facies relationship with Unit 2. Occasional
fire-cracked rocks are found within the upper portion of this deposit, probably
representing the sedimentary reworking of prehistoric Early Agricultural deposits. The
portion of Unit 3 identified in the stratigraphic pit Figure 4.6 represents bank margin
Page 135
view looking S 2 3 -33 E
..f., •4•"y
Vb ;14";" °
111a 4
bottom of
stratigraphic pit
Ma i
11b 2
Ila 2
Ila i
AZ BB: 13: 6 ASM
pebble to cobble grovel
medium sand
silt, channel fades
silty cloy, prehistoric floodplain deposits
coarse sand to cobble gravel
very fine sand separated by cloy band Mof
modern trash deposits
muddy sand (with groundwater
—derived? carbonates)
fine pale brown sand, overbonk flood ladies of lia
medium sand
silt overbonk facies of lia
pole brown coarse to medium sand
coarse sand and pea gravel overbonk flood fades
related to either Unit lia f2 Unit or 11b 1
dark brown silty clay with
soil formation at the upper boundary
reddish brown coarse sand and cobble gravel
laminated coarse to medium sand, magnetite placer
deposits, low ongle trough to horizontal cross—bedding
pale brown sand and grovel
pale yellowish—brown coarse to medium sand
muddy silt and reddish brown medium sand
wet bank margin fades of Unit Ilb i
pole reddish—brown sand and grovel
dark brown cloy
coarse sand and pea to small cobble grovel (2-6 cm)
dark brown compact silty clay
dark reddish—brown coarse to medium sand
pole brown muddy silt, wet bank margin facies of Unit 116 2
Unit 1162 1 and Unit Ilb i f grade to fine sand and coalesce to west
pedo genesis
cloy bonds
fine sand
medium sand
Digital cartography by CEO—MAP, Inc. 1997
coarse sand
silt overbonk facies of Unit 1c3
fine pole brown muddy sand that grades westward
from a coarse to medium sand
series of dark brown cloy and silt bands
In overbank and slockwa ter deposits with
incipient soil formation at upper boundary
brown muddy sand grading westward from coarse
to medium sand which coalesces with Unit Ilc
coarse sand
and pea grovel
;;:"4..•ti. sand, coarse sand,
gravel, and cobbles
cobble grovel
Profile of the Clearwater site stratigraphic pit
numbers in bold represent elevation
in meters above sea level (MASL)
vertical exoggeralion — 2X
in meters along profile face
petrographic sample
Figure 4.6
and channel fill deposits that are either contemporaneous with or postdate the
sediments identified in trench 12.
The 4.5-m stratigraphic pit (Fig. 4.6) was excavated to clarify the relationship
between a historic canal (Canal D, Feature 180) and the alluvial deposits underlying
the canal. An unexpected bonus was the ability to identify channel margin deposits
adjacent to the alluvial fill into which the canal [now part of the A-Mountain canal
system, AZ BB: 13:481 (ASM)] was excavated. The south profile of the stratigraphic
pit is shown in Figure 4.6. A simplified profile demonstrating the inferred relationship
between deposits in trench 12 and in the stratigraphic pit is shown in Figure 4.7. The
location of the cross sections represented by letters A to A' and B to B' is shown on
Figure 4.1. Sandy alluvial deposits (Unit II, allostratigraphic unit 3) underlying the
canal (Feature 180) contained ceramics and shell dating to the Early and Middle
Rincon subphases. These ceramics suggest a minimum age for the deposit of A.D.
950 to 1100. Cultural materials found in the upper portion of this deposit postdate the
prehistoric occupation of the area. Most material on the surface overlying the channel
deposit dates from the Protohistoric to modern periods.
Another unit of alluvium (Unit III, allostratigraphic Unit 5), consisting of bank
slump and channel fill deposits of a later channel, is also found underlying the canal
and adjacent to Unit 3. These deposits, which are described in greater detail below,
may represent historic incision of the river or may predate that incision.
L 1Rin
Allostratigraplzic Unit 4: Historic and Modern Trash and Land Modification
Unit 4 is a series of historic and modern trash deposits representing either the
fill of mined areas or the accumulation of historic and modern trash on the property.
Modification of Units 1, 2, 3 and 5 by historic and modern processes, such as mining,
dumping, and plowing, is included within Unit 4. Because plowing covers the entire
property, Unit 4 is mapped only where it exceeds approximately 37 cm, the depth of
most plowzones.
Allostratigraphic Unit 5: Protohistoric or Historic Channel Alluvium.
Unit 5 consists of a package of sediments exhibiting soft sediment deformation
and low angle trough to horizontal cross-bedding structures. These sediments are
typical of bank slump (channel margin) and channel fill deposits and represent an
incision of the Santa Cruz River postdating deposition of Unit 3. The deposit predates
construction of the historic canal (Canal D, Feature 179). A former channel is visible
in some aerial photos and may be related to Unit 3 or Unit 5.
By using age estimates on archaeological materials found within each of these
units and radiocarbon dates, where available, and by examining the general lithology
and stratigraphy of the units within the project area, the following correlations can be
made with Haynes and Huckell's (1986) units. The ages of archaeological material
found within allostratigraphic Unit 1 correlate with the ages of the upper Unit B2 of
Haynes and Huckell. The geomorphic, lithologic, and archaeological context of these
deposits is consistent with their data. Similar preceramic archaeological materials
have been found in these deposits upstream.
The ages of cultural materials found within Unit 2 correspond with Haynes and
Huckell's (1986) Units C 1 and C 2 . Although cultural materials from a variety of
periods, including the historic period, are found within this deposit, deposition of
cienega sediments probably occurred between 2,500 and 1,000 years ago. A similar
cienega soil is found in the Olberg-Schanck reach of the Santa Cruz River (upstream
of the project area) during this period. As suggested by Ahlstrom et al. (1994),
standing water need not have been perennially present for such deposits to form. It is
possible that the thick, dark brown clay to silty clay deposits are the result of shallow
groundwater and perhaps small spring-fed pools surrounded by wetland grasses and
other hydrophytic vegetation.
The presence of Early and Middle Rincon ceramics in portions of Unit 3
suggests that this channel was active either during or after the period from A.D. 950 to
1100. Rincon phase ceramics were found in dunes overlying Unit C 2 west of
Brickyard Arroyo. Haynes and Huckell (1986) suggest that dune formation may be
related to Unit C3 channel incision. Slopewash deposits of Unit C3 are found upstream
at the Drexel Road site and along parts of Airport Wash. These deposits contain
Tanque Verde phase (A.D. 1150 - 1300) and later archaeological materials. It is
possible that Unit 5 is related to channel activity that was responsible for the
deposition of these slopewash deposits upstream.
Unit 4 can be correlated with Unit D and is essentially historic or modern in
The succession of sedimentary cutting and filling events in the A-Mountain
project area generally fits that found by Haynes and Huckell (1986) elsewhere in the
Santa Cruz Valley; however, further examination of the relationship between deposits
is necessary to confirm whether or not these sedimentary events are concurrent across
the entire valley. Cienega deposits in the A-Mountain project area are potentially
promoted and preserved by the Sentinel Peak volcanic intrusion and by the presence of
shallow, spring-fed groundwater sources. Some of the units identified in the project
area appear to have formed contemporaneously with other geomorphic units, making
the boundaries between time-geomorphic units less obvious. These relationships have
been further obscured by historic modification of the ground surface.
The prehistoric occupation found at the eastern end of the A-Mountain drainage
system is remarkably well preserved and may be due to a number of geomorphic
factors. Overbank or slackwater sedimentation seems to have accumulated on the
downstream side of A-Mountain, allowing preservation of archaeological deposits to
occur. The Early Agricultural period settlement was restricted to a narrow band of
preserved floodplain, which formed a small rise surrounding what would become or
what already was a prehistoric cienega. Periodic inundation by floodwaters of the
Santa Cruz River would have made the cienega an ideal place to exploit wetland
vegetation or to cultivate crops. Both the cienega and the floodplain have undergone
significant modification from prehistoric and historic channel changes of the Santa
Cruz River and from historic and modern human activities, leaving only a tiny
fragment of the prehistoric land surface and the archaeological resources preserved on
that surface.
During summer of 1995, Desert Archaeology, Inc. excavated a series of
trenches along the entire length of Alameda Street west of the Santa Cruz River
(Figure 4.1). The trenches extended from the Santa Cruz Riverpark to Tumamoc Hill.
Exposed in the trenches were prehistoric and historic artifacts and features, including
canals or ace quias which may have been part of an extensive system at the base of
A-Mountain and recorded in historic documents.
According to the Arizona Geological Survey (McKittrick 1988), the portion of
the project area east of Grande is Qt3 and the portion west of Grande is Qt2; however,
data recovery efforts found Holocene sediments across the entire project area.
Because the trenches were not deeply cut, it is difficult to determine whether these
Holocene sediments are identical to those which Haynes and Huckell (1986) describe
as forming a compound terrace with the Jaynes terrace (Qt3) or whether the entire
project area represents the alluvium that comprises the Holocene terrace (Qt2).
The Menlo Park Storm Drain testing project provides a unique opportunity to
glance at a very long profile of surface (< 2 m deep) sediments of the Santa Cruz
River Valley. The following section provides a general description of sediments found
along Alameda Street and generalized in Figure 4.8 and represented by the
cross-section indicated by C to C on Fig. 4.1.
The entire section of sediments exposed during testing consists of alluvial
deposits of the Santa Cruz River, with the exception of minor evidence for colluvial
deposition of clasts coming off the Sentinel Pealc/Tumamoc Hill area in the
westernmost portion of the project area. The alluvial deposits recognized in trenches
are comprised of a single large deposit of cienega-like clays underlain and cut into by
sandier deposits representing channels (both large and small) of the Santa Cruz River.
In places, a silty overbank deposit is preserved on top of this clay band.
Unit 1 consists of a package of sediments that include finer-grained silts and
clays and coarser-grained channel features. Lenses of former channels are found
within the deposit in trenches 8, 9, 10, 11 and 12. This unit may be part of the
Holocene sediments covering the valley floor in this location or may be Pleistoceneaged sediments which form the Jaynes terrace. These sediments are covered by
younger, Holocene-aged sediments, suggesting that if the Pleistocene Jaynes terrace
(Qt3) is present in this area, it forms a compound terrace with the younger Qt2.
Unit 2
Unit 2 represents a series of laminated silts and sands in trenches 2 and 3.
These may be equivalent in age to sediments defined as unit 1 or are younger. Due to
the thickness of overlying units in trenches to the west, the extent of this unit could
not be determined. The bottom portion of the channel contained two thin laminae of
abundant charcoal. Charcoal from the bottom most of these laminae, yielded an age
estimate of 3650 ± 60 B.P. (Beta 85537). A possible pit structure is located in the
upper portion of this deposit and found in trench 1.
Unit 3
Unit 3 is comprised of very dark brown cienega-like clays that are found in the
bottoms of the trenches west of trench 3. These clay loam to silty clay loam deposits
are usually marked by abundant carbonates and angular to subangular blocky structure.
Most of the prehistoric archaeological features found along Alameda St. are dug from
the top of this deposit. If the age of features elsewhere in the area can be used as a
guide, then these prehistoric features probably date to the earlier part of the Hohokam
period. This deposit appears to be a Holocene floodplain sediment overlying deposits
of the Jaynes terrace formation.
Unit 4
Unit 4 represents a silty overbank deposit that overlies the dark brown cienega
clays of unit 3. The unit becomes thicker to the west. Toward the west end of the
project this unit is very thick and interfingers with sheetwash/debris flows off the
Sentinel Peak-Tumamoc Hill complex.
Unit 5
Unit 5 represents a former channel of the Santa Cruz River, identified in trench
2. Three possible canals are found within this channel. The channel cuts through
units 2, 3, and 4. This channel may be a part of a ditch excavated by Sam Hughes in
1888 that began headcutting the following year (Betancourt and Turner 1990).
Unit 6
In few places does an intact "plowzone" (unit 6) appear, indicating that
post-agricultural processes have altered or destroyed evidence for agriculture. In other
words, plowzones were removed or altered to the effect that they are no longer visible
in the soil profile. Since this is unusual in natural floodplain settings, we can assume
that the lack of a plowzone (known to exist from historic records) is due to
post-agricultural destructive processes inhibiting its preservation. The most obvious
process, other than removal or redistribution of the plowzone sediments is compaction
by modern travel and the construction of roadways used for such travel. In places, it
is obvious that the sediments which may have in part formed the plowzone, are highly
compacted. Where sherds are present, the sediments have been pressed to conform
around the shape of the sherd body, suggesting that these sediments became compact
during wetter conditions. It is probable, that when the dirt road that became Alameda
Street was in use, it occasionally became muddy and forced compaction of these
sediments. Further compaction may have occurred when the road was actually paved.
Nevertheless, this upper sediment was deposited sometime after historic use of the
ace quias and before the current construction of Alameda Street.
The project area is located at the confluence of the Santa Cruz River and
Rillito Creek on a finger of land comprising the former floodplains of these streams
(Figure 4.9). The following discussion of the geomorphology will refer to the two
portions of the project area separately. The portion of the project area that
encompasses the Sunset Mesa Ruin (AZ AA:12:10) and the old Sunset Dairy is
referred to as the northern portion of the project area. The portion of the project south
of Sunset Road that encompasses the Rillito Fan site (AZ AA:12:788) is referred to as
the southern portion of the project area.
Figure 4.9. Surficial geology of the Rillito Fan project area (after McKittrick 1988) showing
location of the Rillito Fan site and trenches described in text. UTM coordinates place the map
in its position on the USGS 7.5' quadrangle for Jaynes, Arizona.
Rillito Fan Site (AZ AA:12:788)
Although the confluence of the Santa Cruz River and Rillito Creek is better
known for the Rincon-age Sunset Mesa Ruin (AZ AA:12:10), a recent Late Archaic
component has been discovered by Desert Archaeology, Inc. (Tucson, AZ) south of
the Sunset Mesa Ruin on the site known as Rillito Fan (AA:12:788; Wallace 1996).
The site was surface collected and tested during Fall 1995. Only 853 m of trenching
was placed over a 160 acre area. Twenty-three cultural features, including pit
structures dating to both the preceramic and ceramic periods, clusters of fire-cracked
rock, a homo (pit oven), and various small pits. Most of the features are thought to
date to the Early Agricultural or Early Ceramic period. Although most of the Early
Agricultural component is shallowly buried under the Holocene terrace in what
appears to be sediments from Rillito Creek, the finer-grained materials underlying
these sediments may be derived from the Santa Cruz. A date of 2860 ± 40 B.P. was
derived from charcoal in a pit eroding from the western portion of the site in the
lowest identified cultural layer.
Prior to fieldwork, aerial photographs, topographic maps, and surficial geologic
maps were consulted to determine which areas would be most likely to contain
cultural remains. Test trenches located in these areas were examined for geologic
study. Sedimentary characteristics and stratigraphic relationships were recorded in
order to verify the origin of the deposits and the cultural materials within those
deposits. Soils were described using USDA soil classification criteria, further
elucidating the origin and transformation of sediments within the project area.
Because the project area was potentially influenced by two different drainages,
sediment samples were examined from key localities within both parts of the project
area and compared with reference samples to determine from which drainage
sediments were most likely to originate. The southern wall of the Rillito arroyo,
which was cut during the 1983 flood caused by tropical storm Octave and which
preserves an excellent exposure of the deposits, was examined for additional pertinent
information. Because of the low probability of recovering intact archaeological or
historic resources within T-1 and because previous projects within the Santa Cruz
River valley have demonstrated a high likelihood of recovering archaeological
resources from T-2, test excavations for this project were focused on T-2.
Results of Geomorphic Study
Representative stratigraphie descriptions from the northern and southern
portions of the project are provided in Tables 4.3 and 4.4. These are referred to in the
discussion below where stratigraphic units are described.
Generalized Stratigraphy
Both portions of the project area are comprised of a loose, coarse-grained
component (unit III) underlain at depth by fine-grained sands, silts and clays typical of
overbank, slackwater, and cienega deposits (units I and II). Detailed analysis of these
Table 4.3.
Stratigraphic desccriptions from the south wall of Trench 10, AZ AA:12:788.
(m below
Ground surface.
Plowzone; lower boundary is abrupt and undulating. Occasionally as
great as 50 cm. in depth. Compact, light grayish brown slightly sandy silt
loam. Abundant very fine rootlets present, some bioturbation, and rare
fragments of fire-cracked rock.
Pale brown silt with some very fine carbonates, grades to a heavy silt
loam to silty clay loam at lower boundary; massive. A thin lens (<3 cm
thick) of silty clay forms an abrupt lower boundary with the underlying
deposit. Extensive bioturbation and moderate quantities of rootlets are
present throughout the deposit.
Moderately compact channel deposit which forms a facies within Unit
The lens is comprised of a fine sand in the upper portion of the
deposit and grades vertically to a fine gravel at the base of the deposit.
The sand and gravel are pale brown in color, and are comprised primarily
of granitic particles and abundant flecks of muscovite. The deposit
extends at least 4.3 m horizontally.
Channel sand. The upper portion of the deposit is comrpised of a lightly
compact pale brown fine loamy sand and grades to a very pale brown
coarse sand at the base of the deposit. The sand is granitic and contains
abundant muscovite flecks. Abundant rootlets and fine flecks of charcoal
are present throughout the loose sand at the base of this deposit.
Pale brown silt loam to silty clay loam; massive to granular structure.
Rare fine to medium flecks of charcoal are present throughout.
Dark grayish brown, very compact clay loam; medium subangular blocky
structure. Abundant fine to medium-sized flecks of charcoal are present
throughout. Carbonates are present throughout as coarse sand to very fine
gravel-sized nodules. Cultural material mixed in includes charcoal, firecracked rock, and flaked stone. The concentration of this material here
was labelled Feature 17 and dated 2860 ± 40 B.P. (Beta 90318).
Very compact slightly sandy pale brown silt with a few fine carbonates.
Dark grayish brown clay loam, very compact; medium subangular blocky
structure. Abundant charcoal fine to medium-sized flecks of charcoal are
present throughout the deposit. Carbonates are present throughout in
coarse sand to very fine gravel-sized nodules. No artifacts were observed;
however, only a very small exposure examined. This unit extends beyond
12.56 m below datum but it is unknown to what depth in this locality. At
other sites, similar bands rarely exceed 50 cm in thickness.
Table 4.4.
Stratigraphic descriptions from the north wall of Trench 14, AZ AA:12:10.
Deposit (m below datum) Description
Ground surface.
Zone of surface disturbance; compact pale brown silty sand. No
carbonates visible, abundant fine and coarse rootlets. Muscovite mica
flecks are abundant. Extensive bioturbation.
Loose, pale brown silty sand. No carbonates, same composition as
uppermost stratum. Some fine gravel. Muscovite mica flecks are
abundant. Extensive bioturbation, abundant fine rootlets.
Pale brown silty clay loam; laminated.
d-g, m
Pale to dark brown clay loam, laminated with lenses of pale brown silty
loam. Laminated sedimentary structure still present in places but varies
considerably both horizontally and vertically. Moderate amount of fine
carbonates and rare fine to medium flecks of charcoal are present with the
basal five cm bearing the highest frequency.
Moderately compact, pale brown silt loam. No carbonates, bioturbated.
Rare fine to medium flecks of charcoal. Grades vertically into clay loam
Massive brown silty clay loam with few, very fine carbonates and rare
medium flecks of charcoal. Fine to medium subangular blocky structure.
Pale brown compact fine loamy sand lens. No carbonates or charcoal
Dark grayish brown, very compact clay loam; medium subangular blocky
structure. Abundant fine to medium-sized flecks of charcoal are present
throughout though their density varies considerably along the length of
Trench 14. Carbonates are present throughout in coarse sand to very fine
gravel-sized nodules. May be equivalent to Unit 2B1 south of Sunset
Grayish brown (top) grading to pale brown (bottom) compact heavy silt
loam. Some medium-sized mottles of sediment from stratum above are
present in the upper portion of this unit. Small flecks of charcoal and
carbonates in the form of coarse sand to very fine gravel-sized nodules are
present throughout.
Pale brown compact coarse sandy loam. Rare small flecks of charcoal are
present throughout. At the base of the unit there is a concentration of
dark gray heavy minerals, including magnetite.
Very compact pale brown sandy silt. Extends to an unknown depth.
two components is difficult, given the very limited proportion of ground exposed
during testing; however, some general interpretations can be proposed.
The upper component is composed of massive, poorly sorted sand and gravel
units that are typical of those found on alluvial fans. These massive units are
occasionally punctuated by well- sorted sand and/or silt lenses typical of overbank or
slackwater deposition and other less well- sorted sand channels. The strata within this
upper component cannot be traced over long horizontal distances and are typical of a
braided stream regimen characterized by a network of channels that join and separate
and that are separated by islands or bars (Leopold et al. 1964). While the individual
channels comprising the network may be narrow, the network itself is normally wide
and shallow (Leopold and Wolman 1957). In this system, large flow events such as
floods would have the opportunity to spread out widely across the valley floor. The
presence of a coarse-grained upper component suggests that the braided channel
morphology of Rillito Creek known from historic record also may have existed during
the prehistoric period.
The lower component is comprised of at least three dark brown clay bands,
which exhibit considerable pedogenic development in the form of soil structure and
abrupt to very abrupt boundaries occasionally marked by a darker, organic-rich horizon
in the upper 5 cm. Although these clay bands are similar to cienega deposits, they
generally do not exhibit the darker color and other characteristics of soils that would
support the growth of sedges and other riparian plants. These clay bands, and the silts
and fine to very fine sandy silts that separate them, are typical of overbank and slowmoving or slackwater deposits that are characteristic of an aggrading stream.
Elsewhere along the Santa Cruz River, similar deposits have been discovered. The
abrupt to very abrupt upper contacts of each clay band are often indicative of erosional
or channel-cutting episodes. The upper, organic-rich horizon within each clay band
probably represents the formation of a grassy swale on sediments that have filled a
former river channel.
Apart from proximity to the current channel of the Santa Cruz River and
general similarities among sediments comprising the lower component of the Rillito
Fan site, including the presence of abundant fire-cracked rock and chipped stone
within the uppermost of these clay bands (unit Ilb), there was no particular reason to
conclude that either the upper or the lower strata could be correlated with sediments
found at other sites along the Santa Cruz River. Sourcing of the sediments found
within the project area was necessary to determine which stream(s) most influenced
past sedimentation within the project area. Because the project area is situated at the
confluence of the Santa Cruz River and Rillito Creek, sediments could potentially
originate from either one or both of these streams. The project area is also near the
confluence with Cafiada del Oro Wash, adding yet another source. In fact,
examination of sands from the south bank of the Rillito (T-1) near the northern project
area revealed sands originating in the Canada del Oro system and probably
representing slackwater deposition during the period when the Rillito met the Santa
Cruz near the Catiada del Oro Wash (see Figure 4.10).
18 72
MO 1912
ME 1937
— -- 1941
MIDI 1960
- 196 7
ME 1980
Linsberlest Drive
Figure 4.10. Historic channel locations along Rillito Creek (after Graf 1984).
Fine- and coarse-grained sand samples from the upper component (unit IV)
were examined by petrographers Beth Miksa and Michael Wiley of Desert
Archaeology. By using a set of reference samples taken from various localities within
the Tucson Basin, they were able to determine that the upper strata in both the
northern and southern portions of the project area are comprised of sands that originate
within the Rillito Creek system.
Provenance is more difficult to assess on fine-grained materials (i.e., clays,
silts); however, some portion of coarser material is nearly always present in finegrained sediments. Occasionally, within the uppermost clay band (Unit lib), somewhat
discrete features can be identified. Two such features (Features 17 and 24) were
identified on the eastern and western edges of the Rillito Fan site (AZ AA:12:788).
The coarse components recovered from flotation samples derived from these features
were examined by petrographer Jim Heidke of Desert Archaeology. Examination of
the coarse component recovered from those features exhibited abundant carbonate
nodules and fragments of volcanic rocks. No metamorphic rock fragments were
identified; therefore, the sediments are likely derived from the Santa Cruz River.
Correlation and Dating
A single radiocarbon age estimate on a feature (Table 4.3, Feature 17) within
unit IIb yielded a date of 2860 ± 40 B.P. (Beta 90318). This date correlates well with
the upper part of Haynes and Huckell's unit B 2 . Correlation between this site and the
Los Pozos site [AZ AA:12:91 (ASM)] suggests that deposition of this unit corresponds
with the Early Agricultural horizon at the Los Pozos site. This deposit, at Los Pozos,
is followed by a significant period of channel incision. If the correlations between the
two sites are correct, changes in channel morphology and direction of the Santa Cruz,
which may have resulted from this episode, may explain the incursion of Rillito
Creek-derived deposits (unit IV) at the Rillito Fan site. Additional exploration of
exposures along the Santa Cruz could potentially resolve any questions regarding the
origin and correlation of these sediments.
Correlation between deposits in the northern and southern portions of the
project area is much more difficult to assess. The northern portion of the project area
is highly influenced by its location at the confluence of two streams. In the deepest
exposure (trench 14) on the northern portion of the project area, thin bands of
sedimentation (Table 4.4, deposits b-g and m) in the vertical center of the exposure
likely signal the transition between Santa Cruz and Rillito deposition, and they may
even represent interfingering deposition from these two streams. In this location,
transition between the two systems likely occurred over a longer period of time than
the fairly abrupt sequence displayed in trenches on the southern portion of the project
Prehistoric Geologic Setting
The generalized stratigraphy suggests that sedimentation within the project area
occurred in two phases. First, slow-moving aggradational deposits of the Santa Cruz
River were emplaced within the project area. Toward the end of this sequence, the
remains of a substantial prehistoric occupation were deposited within a clay band (unit
lib). These people were probably living on or near a grassy swale floodplain of the
Santa Cruz River. Either during or shortly after this occupation, the Santa Cruz
channel changed course, eventually allowing Rillito Creek sediments to be emplaced
within the project area. A substantial hiatus probably occurred before the project area
was again inhabited.
Clearly, a major change occurred in the physical environment of the project
area. The incursion of Rillito Creek derived sediments into the project area represents
a markedly different depositional system. Rillito Creek was a wide, shallow braided
stream during the later prehistoric occupation. The site area itself was likely part of a
wide floodplain that occasionally flooded during larger storm events. The river was in
a state of dynamic equilibrium, meaning that aggradation and degradation (small scale)
occurred in several reaches at the same time. Large base-level changes, which occur
during periods of net degradation or channel incision, were clearly not the norm. The
channel itself probably migrated widely in its course; however, the presence of
prehistoric cultural material within the project area and evidence for incipient soil
formation suggest that the site area itself was part of a wide fan of material being
deposited and eroded only in flood-scale events.
Landscape Stability
Although channel morphology can have some effect on the selection of a site
for habitation or agricultural activities, a more important criterion is landscape
stability. Braided streams can be easily erodible, but the presence of carbonates and
organic matter typical of soil formation can indicate that stable surfaces existed in the
prehistoric past. In both the northern and southern portions of the project area, loose,
coarse-grained sands are often separated by finer-grained silts in the upper strata.
These silts are weakly to moderately cemented with carbonates, forming an incipient
soil and representing a surface on which people are more likely to conduct relatively
short-term activities. Many of the features discovered in the southern portion of the
project area appear to be cut into these compact silts. Though interrupted by periodic
incisions, the landscape comprising the lower component is clearly a more stable
environment. Soil development on each of the dark brown clay bands is clearly
stronger and represents a longer period of landscape stability. Upstream of the project
area, the later prehistoric (Late Archaic) occupation consists of large pithouse villages,
which were probably occupied over a substantial period of time.
Another important factor related to landscape stability is the preservation of
cultural remains. The abandonment of the T-2 terrace provides an ideal setting for the
preservation of cultural materials. Since the landform is not being actively eroded by
the river, few other natural processes are available to remove cultural material from its
buried context in the floodplain. However, cultural factors such as the historic use of
the land for farming can move or remove subsurface cultural materials. The surface
of the southern portion of the project area is particularly flat, suggesting that some
land leveling took place prior to plowing. This fact, combined with variable
preservation of stratigraphic units across the field, suggests that small rises and dips
that naturally form in a bar and swale topography were leveled to form a single
surface, thus mixing stratigraphic units of different ages. This is particularly evident
in the southwest portion of the project area.
Finally, location within the stream system affects the amount of active erosion
or deposition that may have taken place in the past. The Sunset Mesa site appears to
have been geomorphically active for a longer period of time than the Rillito Fan site,
which is perhaps why the occupations found on that portion of the terrace date to a
later time period.
Ina Road forms the northern boundary of the study area. Three sites are
located along the portion of Ina Road from the railroad tracks just east of Interstate-10
to Silverbell Road. These archaeological sites, AZ AA:12:111, 130, 503, and 688
have been reported by several different individuals or companies and should probably
be lumped under one or two archaeological sites.
AZ AA:12:111/688
Site AZ AA: 12:111 was discovered during subsurface trenching for a sewer
line, and was further defined by Bruce Huckell and C. Vance Haynes (1979, ASM site
files). The site consisted of at three buried occupation horizons associated with
chipped stone, fire-cracked rock, charcoal, and animal bone. The subsurface
horizontal extent of the site covered about 800 sq m. Radiocarbon dating of these
horizons placed the use of the area between approximately 2,800 and 4,300 B.P.
(Huckell 1988:65). The western locus of AA: 12:111 is within the boundaries of
AA: 12:688, which was identified during subsurface testing in 1988 (Bontrager and
Stone 1989). Four deeply buried (8-10 ft) archaeological features were identified in
over 150 linear ft of trenching. A radiocarbon date of 2775 ± 45 B.P. was obtained
from carbonized wood found within a cultural feature (Bontrager and Stone
1989:Table 1). The site was recommended for National Register of Historic Places
AZ AA:12:130
AZ AA:12:130 has also been reported by Haynes and Huckell (1986). Cultural
remains are known to extend to 4.3 (14 feet) below the modern ground surface.
Radiocarbon dates of 3260 ± 100 B.P. (A-3145), 3730 ± 110 B.P. (A-3104), 3240 ±
50 B.P. (A-3147), and 3140 ± 90 (A-3146), were recovered from limited work at the
site. A small portion of the site was tested by SWCA Environmental, Inc. (Tucson,
AZ) in Fall 1996. A few possible features and isolated artifacts were found. A short
examination by the author confirmed the sequence of sedimentary deposits previously
reported by Haynes and Huckell (1986); no additional sedimentary profiles were
AZ AA:12:503
AZ AA: 12:503 was originally recorded as a low density artifact scatter
containing abundant shipped stone debitage and tools, fire-cracked rock, ground stone
fragments, and occasional sherds covering a 13 acre parcel on the floodplain east of
the Santa Cruz River and north of Ina Road. Diagnostic ceramics included one
Canada del Oro red-on-brown, one Santa Cruz red-on-brown, and a few Rincon
red-on-brown sherds (ASM site files). Surface disturbance, due to modern
development, was heavy and the exact boundaries of the sites remain undefined.
In 1987, AZ AA:12:503 was tested with 235 m of backhoe trenches by Desert
Archaeology, Inc. (then the Tucson branch of the Institute for American Research;
Doelle 1987). One cultural feature, unidentified as to type at that time, was identified.
Given current information, that features may have been a burned pit structure dating
prior to A.D. 1. Statistical Research, Inc. (Tucson, AZ) has recently completed
excavations in an area north of the current project area (Ezzo and Deaver 1996).
These excavations identified a total of 208 cultural and natural features. One pit
structure was exposed. Radiocarbon dates recovered during the course of these
excavations suggested that the site was occupied during the San Pedro phase
(1200-800 B.C.; Ezzo and Deaver 1996).
During Spring 1995, Desert Archaeology, Inc. (Tucson, AZ) tested a linear
alignment along the south side of Ina Road from Silverbell Road to a point
approximately 0.2 km west of the Interstate. A few possible pit structures were found.
The author was able to confirm, by only cursory examination of trench sediments, that
the sedimentary deposition along Ina Road, exposed in the trenches, was similar to
that noted by Haynes and Huckell (1986) and Ezzo and Deaver (1996) elsewhere in
the area.
Geologic Background
Surficial deposits within the project area were mapped by the Arizona Geologic
Survey in 1988 (McKittrick 1988, Figure 4.11). The project area comprises the
alluvial fan deposits (M2) at the very western edge of the project area and the
Holocene floodplain of the Santa Cruz River (Qt2). Testing did not extend far enough
to reach the Pleistocene terrace (Qt3) of the Santa Cruz River. The historic
floodplain, labelled Qt 1 by the Arizona Geologic Survey, was not encountered in any
of the trenches; however, significant modern disturbance is present near the channel
thalweg where the Ina Road bridge was installed. Interfingering between alluvial fan
sediments and Holocene terrace sediments occurs in trench 3.
3578000 m N
Figure 4.11. Surficial geology in the Ina Road area (after McKittrick 1988) showing relevant
archaeological sites and geologic cross-sections. UTM coordinates place the map in its
position on the USGS 7.5' quadrangle for Jaynes, Arizona.
The project area is located immediately downstream from the confluence of the
Santa Cruz River and the Canada del Oro. The influx of sediments from the Canada
del Oro significantly affects sedimentation in this part of the Santa Cruz River. In
addition to providing different source materials for sedimentation in this part of the
valley, the geomorphic processes acting on a reach where a significant drainage adds
it's discharge to the total discharge of the valley produces distinct depositional results
(effects). In the case of this reach of the Santa Cruz, sediment deposition appears to
be fairly continuous with little chance for incipient soil development.
Previous Geochronologic Work in the Project Area
In 1979 and 1980, Bruce Huckell and Vance Haynes examined prehistoric
features exposed in a trench excavated for a sewer line and excavation for the Ina
Road landfill. They derived several dates on geologic units exposed in the excavated
trenches and have correlated these units with their geochronologic investigations
elsewhere in the Santa Cruz Valley (Haynes and Huckell 1986). The two upper units,
which extend at least five feet below the surface along most of Ina Road and pinches
out on the east side of I-10, date to between 2846 ± 73 (average of 4 dates) and 1400
± 220 (A-3141) years B.P. Weak soil development separates these silty sand deposits
from the underlying geologic deposits. These underlying deposits date approximately
4260 ± 140 (A-2234) and 3222 ± 43 (average of three dates). Continued excavations
in 1980 for the Ina Road landfill revealed a number of preceramic fire hearths 3.5 to
4.5 meters below the modern floodplain. At least one of these hearths consisted of a 2
m diameter mixture of cobbles and charcoal (Haynes, personal communication, 1997).
Radiocarbon dates on these features yielded dates between 3700 and 3100 years B.P.
(Haynes and Huckell 1986).
Recent Excavation At AA:12:503 (ASM) by Statistical Research
During summer and fall 1995 Statistical Research conducted testing and data
recovery at AA: 12:503, named the Costello-King site. They identified four strata,
each containing cultural material. The uppermost deposit is predominantly a clay and
contains Rincon phase ceramics. Underlying this horizon is a rather thick deposit
variably classified as silty slackwater deposits and "fossil channels" which they
characterize as the distal portion of the Canada del Oro alluvial fan (Ezzo and Deaver
1996). Artifacts and features within this deposit date to roughly 2700 B.P. This unit
is underlain by another deposit of clay, which was not extensively investigated.
Recent Excavation at AA:12:130 (ASM) by SWCA
In November of 1996, SWCA Environmental, Inc. excavated five trenches east
of the Santa Cruz River and south of Ina Road. The first three trenches were placed
at an angle approximately parallel to the current channel of the river. Trenches 4 and
5 followed the proposed effluent pipe realignment to the south. Trench placement was
fortuitously advantageous for compiling a cross-section of prehistoric and historic
sedimentation. The trenches were located on a relatively flat parcel of land near a
large pit excavated as part of the landfill operation. Tree growth in the pit indicates
that the pit has been present for several years, perhaps decades. The upper meter
(approximately) of sediment on the flat parcel where the trenches were located is
comprised of modern fill.
Two prehistoric sedimentary units were recognized in SWCAs trenches. The
westernmost sediments are young in age, and represent a late prehistoric to
protohistoric channel of the Santa Cruz River. This channel (or set of channels) is
present upstream and has been identified at the Los Pozos (AZ AA:12:91) and
Wetlands (AZ AA: 12:90) sites (Freeman 1997). Bedding structures are still visible in
both sandy and silty sediments indicating that they were once part of channel filling
events and that these events have not been subsequently altered by soil forming
At the easternmost end of trench 2 and continuing in trenches 3 through 5 were
a series of clay and silt bands. The boundary between these floodplain deposits and
the younger channel contained several ephemeral features of charcoal and fire-cracked
rock. Plain ware sherds were found underlying these features. The uppermost of
these clay bands probably represents the pre-incision floodplain margin of the Santa
Cruz River, sometime during the Hohokam period.
The lower series of clay bands (which are best represented in trenches 3
through 5) represent slightly older floodplain sediments. Carbonates appear in few,
fine filaments and there is little other evidence for long episodes of pedogenesis. A
single shallow channel was present within this package of sediments. It is possible
that these units are equivalent in age to the units described by Haynes and Huckell
(1986) nearby; however, they are probably slightly younger, given the relative position
and apparent age of the sediments (probably somewhere in the range of 1400-2700 yrs
Results of Testing Along Ina Road
Excavation of backhoe trenches along Ina Road revealed a 1500 m profile of
alluvial sediments. West of the Santa Cruz River, at AZ AA:12:315, the sediments are
characterized by alluvial fan sediments and Holocene alluvium derived from the Santa
Cruz River. Neither the archaeological features nor the geologic strata provided
significant distinguishing characteristics to assess the age of these deposits.
East of the Santa Cruz River, at AZ AA: 12:503, the sediments are
characterized predominantly by overbank and slackwater deposits of the Santa Cruz
River. Shallow channels, similar to those identified by Statistical Research at the
Costello-King site and by the author at AZ AA: 12:130 were encountered in some
trenches. The succession of sediments was relatively homogeneous across the
trenched area, indicating that the profile drawn by Haynes and Huckell (1986; Figure
4.12) is representative of the general stratigraphy. Although it is difficult to assess the
reliability and significance of a single radiocarbon date, it appears that stratigraphy
containing intact artifacts and features dating to approximately 2400 yrs. B.P. is
preserved in at least a part of the project area.
Brook sachon
3240 t 50(A-3147)
3730 t 110 (A-3104) 3260 t100(A- 3145) 1970 t 310(AA- 319)-
••••• ..... .••
2700t 130 (A-2453)
1-1400 220 (A-3141)
1-2820±2130 (A-2237)
2720±210 (A-2452)
2970±100 (4-2451)
42601140 (A-2234)
B I C?)
2150 -
Figure 4.12. Generalized diagram of alluvial stratigraphy along Ina Road (from Haynes and
Huckell 1986).
Correlation between the work conducted by Haynes and Huckell in 1979 and
1980 and the present excavations suggests that the present excavations recovered data
from only the up per units described in their report. The radiocarbon age estimate
suggests that features recovered during testing along Ina Road represented an age
equivalent to the middle portion of Haynes and Huckell's (1986) unit C2. Their
limited testing did not recover artifacts and features dating to this period in this
portion of the Santa Cruz River Valley.
Although only limited excavation and testing has been conducted along Ina
Road, some preliminary conclusions can be suggested regarding the nature of stream
behavior along this portion of the Santa Cruz River. The project area appears to be
aggrading through the entire prehistoric sequence represented in this reach, beginning
around 4000 B.P. Sometime during the late prehistoric or protohistoric period, the
river has incised, forming the boundary between the two units identified in trenches
excavated by SWCA. This "sediment storing" behavior is atypical of upstream
reaches of the Santa Cruz River, where periodically throughout the prehistoric
sequence, the river incised, sometimes to depths of at least 2 or 3 meters. This
process, which involves aggradation and degradation simultaneously occurring in
different reaches of the same river system, is known as "complex response" (Schumm
1973; Schumm and Parker 1973). The river forms a sort of distal alluvial fan in this
reach of the river. During those periods of incision, it appears that the stream forms a
braided system, probably as a result of high levels of sedimentary input from all parts
of the fluvial system upstream (the Santa Cruz River, Rillito Creek, and the Canada
del Oro Wash).
Sites AZ AA:12:502 and AZ AA:12:750 are located along the margin at which
alluvial fans originate in the Tucson Mountains enter the Santa Cruz River Valley
(Figure 4.11). This margin is nearly perfectly matched with the northwest to southeast
trending Silverbell Road. Older alluvial fans are typically found on the west side of
Silverbell Road. The floodplain and terraces of the Santa Cruz River are typically
found on the east side of Silverbell Road. The sites are located on a portion of the
floodplain that has been alternately mapped by the Arizona Geologic Survey as either
the youngest terrace of the Santa Cruz River or alluvial veneers that mantel older fan
surfaces (McKittrick 1988). However, neither of these descriptions accurately reflect
the origin of the sediments found in archaeological test trenches.
Both sites are bounded northwest and southwest by older alluvial surfaces
which no longer exhibit fan morphology. These surfaces (labelled Qtbf by AGS) are
dissected by interfluves composed of younger alluvium (labelled M1 and M2). The
examined archaeological test trenches were predominantly located on the east side of
Silverbell Road in alluvium that was transported by the Santa Cruz River. The
sediments exposed in archaeological test trenches consisted predominantly of finegrained silts and clays representing overbank or slackwater deposits of the Santa Cruz
River. The location of the archaeological test trenches at the boundary between the
interfluves and relatively young alluvium probably promoted the deposition of these
fine-grained materials.
Archaeological features at site AZ AA:12:750 appear to be cut from or
overlying a weakly developed paleosol. The features are preserved by deposition of
additional bands of fine-grained silts and clays. Subtle evidence for pedogenesis is
found within these younger bands.
A fairly well-developed paleosol laden with abundant large stringers of calcium
carbonate is found well below archaeological features discovered at AZ AA:12:502.
The exception, a burned surface is located below that paleosol and likely represents a
natural fire. This feature appears to have been formed atop another, older paleosol;
however, the sediment on which the feature was discovered was not exposed
adequately in the trenches to determine its pedogenetic properties.
Archaeological features at both sites are preserved in floodplain sediments of
the Santa Cruz River. These sediments are appear to be similar in age to those found
within the Holocene terrace of the Santa Cruz River (labelled t2 by AGS). Numerous
sites dating to the Early Agricultural and Early Ceramic periods have been found these
deposits elsewhere along the floodplain of the Santa Cruz River.
Recent excavation between A-Mountain and Ina Road has begun to fill in a
critical portion of the alluvial record. However, the records gained demonstrate a
critical aspect of alluvial stratigraphy, not all records are equal. Many of sequences
described represent different portions of the channel system. Some deposits represent
the fill of paleochannels or the channel margins, while other parts of the record
represent the floodplain component of the record. The relationship between the
paleochannel and the floodplain components are rarely observed in a single reach, as
archaeological testing normally attempts to excavate the areas in which archaeological
sites will be preserved and erosion of the current channel often exposes the younger,
poorly-consolidated sediments. Utilizing the radiocarbon record or the presence of
archaeological materials as a guide, these records can be chronologically correlated.
The numerous geologic sections presented also demonstrate that although
chronological correlation is possible, the records from different reaches may exhibit
different fluvial processes. The differences between these reaches are important in
interpreting the way in which prehistoric people could have used the river and the
manner in which channel changes took place.
1. In places, these unconsolidated sediments appear to be inset against a buried late
Pleistocene terrace (Qt3).
The Santa Cruz Bend (AZ AA:12:746, ASM) and Juhan Park (AZ AA:12:44,
ASM) sites are located in a sharp bend of the Santa Cruz River, just west of Interstate
10 near the Miracle Mile interchange (Figure 5.1). The abrupt turn of the river here
has exposed prehistoric alluvium on both banks of the arroyo. Archaeological
investigations conducted at both sites between 1993 and 1996 and geologic
investigations of Holocene alluvium at both sites have contributed a high-resolution
record of human use of the floodplain as it transformed during the middle to late
The Santa Cruz Bend, Square Hearth (AZ AA:12:745, ASM), and Stone Pipe
(AZ BB: 13:425) sites were investigated by Desert Archaeology, Inc. between 1993 and
1995. Large-scale excavations were carried out at these sites as a part of cultural
resource management investigations of the Interstate 10 corridor. The vast horizontal
extent of these early farming villages literally changed the face of Tucson Basin
The three sites produced radiocarbon dates spanning the period from 2500 to
1600 B.P. Radiocarbon dates from the Santa Cruz Bend site fall at the early end of
Square Hearth stratigraphic pit
Figure 5.1 Surficial geology of the Juhan Park and Santa Cruz Bend site areas showing
relevant geologic cross-sections and stratigraphic profiles. UTM coordinates place the map on
the USGS 7.5 topographic quadrangle for Jaynes, Arizona.
the spectrum, dates from the Square Hearth site fall at the late end of the spectrum,
and dates from the Stone Pipe site are bracketed by dates from the other two sites.
The sites exhibit characteristics that appear to reflect a trend toward sedentism (Mabry
1996a). Although the foci of the geologic studies described in this chapter are the
Santa Cruz Bend and Juhan Park sites, Stone Pipe and Square Hearth are also
described briefly below.
Santa Cruz Bend (AZ AA:12:746)
The Santa Cruz Bend site is located just east of the Santa Cruz River and west
of the Miracle Mile interchange. The exposed (excavated) portion of the site covered
roughly one hectare; however, the site is estimated to cover approximately eight
hectares. Because the right-of-way was not restricted to a linear exposure, more
detailed information regarding site structure could be gleaned from this site.
Sixty-three Cienega phase pit structures and numerous extramural pits were completely
or partially excavated at the site. One large structure, which may have been used for
communal or ceremonial activities, was found in the northwestern portion of the site.
Numerous other features were recorded in trenches or exposed during backhoe
stripping but unexcavated. It is estimated that a total of 2,400 features may have been
present prehistorically.
Mabry (1996a) defined five classes of pit structures based on size of the
structure and types of features inside the structure. He believes that these features
may have served different functions. Some of the pit structures appear to form
circular clusters, which may have been the domain of an extended family.
All pit structures at the site consist of shallowly-excavated, round subsurface
depressions. Within these depressions are small and large intramural pits. Formal
intramural hearths are rare. Those pit structures thought to be used for storage contain
numerous large (1 m diameter, 1 m deep) intramural pits and tend to have a smaller
surface area, while habitation structures contain shallow, informal depressions that may
have served as resting places for household items and have a larger surface area.
Some storage structures were found in the center of household clusters. No formal
entries are present within these pit structures, however, larger gaps in posthole spacing
may have served as an entryways.
Stone Pipe (AZ BB:13:425)
The Stone Pipe site was excavated in a single narrow strip along the east side
of Interstate 10 between Speedway Boulevard and Grant Road. A small portion of the
site is located on the opposite side of the freeway. The excavated site area covers 250
m by 25 m, though the highest concentration of structures is located in an area
one-half that size. Twenty-five of the dated pit structures at the Stone Pipe site date
to the Cienega phase, while 15 of the dated structures date to the Agua Caliente phase
of the Early Ceramic period. Numerous other structures were not dated. Some of the
Agua Caliente phase structures were rectangular in shape, distinguishing them from the
round, Cienega phase structures. Some of these later structures also exhibited features
that indicate greater labor investment in building the structure, such as plastered
hearths and walls, and formal entryways flanked by adobe pillars (Mabry 1996a).
Square Hearth (AZ AA:12:745)
The Square Hearth site is located on both sides of Interstate 10, just north of
Miracle Mile and may simply be an extension of the Santa Cruz Bend site. The
exposed portion of the site measures approximately 40 m by 40 m. The site is much
lower in feature density than the Santa Cruz Bend site. Radiocarbon dates on pit
structures from the site differentiate it from Santa Cruz Bend, placing it firmly within
the Agua Caliente phase of the Early Ceramic period. Four round structures and one
rectangular structure were found. Although the sizes of individual structures vary, the
average structure found at the Square Hearth site was generally larger and deeper than
the average pit structure found at Santa Cruz Bend, and most contained raised square
hearths and entryways flanked by adobe pillars. At least two of the structures had
plastered floors and walls. Both the depth of the structure and plastered features
indicate a substantial increase in labor investment over the structures at Santa Cruz
Juhan Park (AZ AA:12:44)
Originally discovered and recorded in 1957, this site is located directly across
the Santa Cruz River from Santa Cruz Bend. A flexed burial was discovered at 2 m
depth along the river bank. During subsequent surveys, Rillito Red-on-brown and
Salado and Gila polychrome sherds were discovered on the bank surface along with
several pieces of flaked stone; artifacts dating to the Hohokam period are still found at
the surface along the northwestern portion of the site. Several roasting pits are also
visible on the surface. During Spring 1996, Desert Archaeology conducted
archaeological testing of the parcel. Few archaeological features were found; however,
both the surface distribution of artifacts and the few subsurface features identified
indicate that an Early Agricultural occupation is present in at least part of the project
Implications of Excavations at the Santa Cruz Bend,
Stone Pipe, and Square Hearth Sites
A variety of other evidence from the sites has been used to support the trend
toward sedentism. These include the initial production of pottery, the establishment of
trade networks, and tool recycling (Mabry 1996a). Although the presence of
numerous structures does not necessarily imply sedentary settlement, site structure and
structural features indicate that some degree of permanency of settlement was
practiced. For instance, few of the pit structures overlap, which may indicate either
memory of former structures or the present remains of those structures. Large storage
features and increased investment in construction during the Early Ceramic period
favors year-round occupation and over-wintering at the site. The presence of large
communal or integrative structures may be evidence that some form of community
organization (e.g., ceremonial activities, meetings, etc.) was taking place during this
As demonstrated in Table 2.1 (Chapter 2), maize ubiquities at these sites are
very high. This, combined with the very high capacity for storage, suggests that Early
Agricultural and Early Ceramic period floodplain sites received a major portion of
their diet from maize agriculture. Unfortunately, there are no winter indicator plants
that might confirm the presence of people at the sites during this season (L. Huckell
1996); however, the remainder of the plant assemblage suggests a nearly year-round
occupation of the sites. In addition to maize, the Santa Cruz floodplain sites produced
evidence for beans, squash, cotton, and tobacco. The rapid introduction of additional
cultivated plants provides further proof that these groups were well on their way to
becoming agriculturally dependent and that by the Early Ceramic period, the plants
that formed the basis for Hohokam subsistence were already in place in southern
Arizona. While numerous wild plants were also exploited, most could be found in
surrounding biotic communities formed on the bajadas of the Tucson and Santa
Catalina Mountains (L. Huckell 1996).
Evidence from palynology at the sites supports the presence of an environment
favorable to plant cultivation. The presence of cattail (Typha) pollen suggests that
perennially-wet sediments were present near the site. Mesquite (Prosopis), willow
(Salix), hackberry (Celtis), and sedge all indicate at least seasonally damp soils in the
vicinity of the sites. The status of the floodplain is better understood by examination
of the geology of the site area.
Geologic investigations at the Santa Cruz Bend and Square Hearth sites were
conducted by Bruce Huckell in 1993 and 1995 and published in a synthetic volume
dealing with those sites (Mabry 1996a). In addition to two relatively narrow but deep
stratigraphic pits at the Square Hearth and Santa Cruz Bend sites, Huckell (1995)
mapped a 140 m long exposure along the right bank of the Santa Cruz River.
During spring 1996, the left bank of the river directly across from the Santa
Cruz Bend bank exposure was mapped as part of archaeological investigations at the
Juhan Park site (AZ AA:12:44, ASM). The Santa Cruz River takes a sharp bend to
the west here, exposing a vertical wall of sediments in places 6 m high. A 600 m
profile of the left bank of the river was mapped using electronic mapping techniques,
supplemented by hand-drawn profiles.
These mapped localities are within 3 km of the Los Pozos site. Because of
their close proximity to the Los Pozos deposits and the quantity of exposed and
documented sediments, correlation between geologic events in the Santa Cruz Bend
site area and the Los Pozos site area (the focus reach) should reflect the relationship
between intrinsic geomorphic processes and the preserved results of those processes
more accurately than correlation between geologic events over the entire Tucson reach
(the study area). The first part of this chapter summarizes the results of Huckell's
research in this area. The second part describes the results of mapping efforts along
the Juhan Park side of the river.
Description of the Area
The Juhan Park and Santa Cruz Bend sites are located on surfaces defined by
the Arizona Geological Survey (Jackson 1989; McKittrick 1988) as representing Qt 1,
Qt2, and Qt3 (the Holocene and Pleistocene terraces; see Figure 5.1). Though the
defined boundaries of these mapped units would probably be changed on the basis of
intensive subsurface investigation, all three terraces are represented in this general
area. Because all three terraces are present, the banks of the river, which cut through
these surfaces, reveal a remarkable history of alluvial cutting and filling events.
The Santa Cruz Bend Profile
Huckell (1996a) defined six stratigraphic units in the right bank profile and
stratigraphic pits excavated at the Square Hearth and Santa Cruz Bend sites dating
from at least the Middle Holocene. Summary descriptions are given below'.
Unit 1 is comprised of a sandy coarse gravel, firmly cemented with calcium carbonate.
The contact between units 1 and 2 along the river bank was sharp and erosional, while
in the two stratigraphie pits this same contact was gradational. Huckell (1996a)
attributes this to the small exposure of the unit in the two stratigraphic pits and the
well preserved nature of the contact and erosional features in the bank profile.
Unit 2 is comprised of an arkosic sand. Dispersed calcium carbonate occurs
throughout the deposit and is prominent in the upper 50 cm. In the two stratigraphic
pits, a thin clay-rich B-horizon overlies this sandy unit. Carbonate concentrations in
the two stratigraphic pits rise sharply beneath the clay horizon and peak at 60 cm
below the clay. The upper contact in the two stratigraphic pits is sharp whereas at the
riverbank the contact is gradational. Huckell attributes this to possible erosion of the
clay B-horizon at the riverbank profile.
Unit 3 is a pinkish brown silty clay. This unit is hard in consistency and
contained abundant small nodules of calcium carbonate, particularly in the upper
portion of the unit. In both stratigraphic pits, the upper portion of the unit contains
abundant organic matter constituting an A-horizon and no evidence for erosion of the
paleosol. Microstratigraphy, in the form of thin (2-10 cm) dark gray organic clay
bands separated by lighter-colored bands, is present along the riverbank, suggesting
that it received sedimentation from floodwater.
Unit 4 is comprised of a series of clay and silt bands which vary in number
and thickness. In the riverbank, the lower portion of this series of bands forms two
clay-filled channels, which Huckell calls charcos. He suggests that the two channels
are either backwater sloughs of abandoned channels or filled crevasse-splays (upstream
channel breaches). He favors the latter interpretation, noting that channel cutting and
filling does not appear to be of long duration. Small calcium carbonate nodules were
found dispersed throughout the channel and manganese and iron oxide stains were
found on ped faces. A few scattered pieces of fire-cracked rock and a single piece of
flaked stone were discovered in the riverbank profile.
Unit 5 is a light brown sandy silt to silty sand. Early Agricultural period
artifacts and features were present within this sedimentary unit. Two zones of
pedogenic carbonate were noted in the stratigraphic pits.
The top of unit 5 is eroded and truncated and unit 6 sediments are deposited in
a channel fill and on top of unit 5. Both historic trash and prehistoric artifacts are
found within unit 6 and Huckell believes that the cutting event may have taken place
as late as the Rincon phase of the Hohokam Sedentary period (ca. A.D. 1100-1150).
Radiocarbon Dates and Correlation
Radiocarbon dates on the charcoal from the riverbank profile and the
stratigraphic pit are reported and compared in Table 5.1. Many of the radiocarbon
dates were run on dispersed charcoal which must be used carefully in
Table 5.1.
Radiocarbon dates on alluvial stratigraphic units at the Santa Cruz
Bend and Square Hearth sites (as reported by Huckell 1996a).
Riverbank Profile
2360 ± 60 (Beta 81057)
Strat. pit
1770 ± 60 (Beta 80152)*
Strat. pit
410 ± 60 (Beta 81049)**
2440 ± 70 (Beta 87067)
3600 ± 60 (Beta 87068)
3800 ± 50 (Beta 81054)*
2290 ± 60 (Beta 81053)** 3830 ± 60 (Beta 81047)
4610 ± 50 (Beta 81056)
3740 ± 60 (Beta 81050)
4380 ± 60 (Beta 81048)
Asterisks denote date considered questionable (*) or probably in error (**).
All dates are uncorrected AMS assays on wood charcoal.
alluvial stratigraphy. Criteria for accepting or rejecting radiocarbon dates are
established by evaluating the context and pretreatment results of each sample. Huckell
(1996a) has rejected several of these dates and his reasons for doing so are outlined
A radiocarbon date on charcoal from unit 2 of the Square Hearth stratigraphic
pit yielded an age estimate of 4380 ± 60 B.P. Overlying unit 3 along the riverbank
yielded an age estimate of 4610 ± 50 B.P. The presence of abundant evidence for
rodent disturbance in the stratigraphic pit caused Huckell (1996a) to favor the
radiocarbon date from the riverbank profile and to suggest that the date from the
Square Hearth stratigraphic pit is "somewhat too young." Huckell (pers. comm. 1997)
suggests that older evidence of bioturbation, which may be unrecognizable, may have
transported the charcoal in unit 2 from one of the younger units above.
Two radiocarbon assays from the base of the organic part of the unit 3 soil
yielded identical age estimates of 3740 ± 60 B.P. Huckell suggests that these dates
also may be just slightly too young. He suggests that both flecks may derive from a
single tree root that burned and was incorporated into the unit 3 paleosol. A similar
date of 3830 ± 60 B.P. was determined from charcoal in overlying unit 4
approximately 10 cm above the unit 3 paleosol. Also in unit 4 of the Santa Cruz
Bend stratigraphic pit was a sample yielding an age of 2290 ± 60 B.P. Because the
late preceramic archaeological site was located 1.5 m higher in the section and because
dates on features at that site were between 2,000 and 2,400 years old, Huckell rejects
the date, again proposing that the charcoal is intrusive into the unit from an
imperceptible rodent hole.
Four age estimates were recovered from unit 5. The first date of 2360 ± 60
was obtained on charcoal from the vicinity of the cluster of fire-cracked rock in the
riverbank profile. Another date on a small channel in the riverbank profile, which
appears to be cut from a vague soil boundary at the level of this fire-cracked rock
concentration, yielded an age of 2480 ± 70 B.P. The channel may have been a
cultural feature, such as a drainage ditch (Mabry 1996a), or may be a natural erosional
feature. These dates conform with the Early Agricultural occupation at the site. A
date of 410 ± 60 B.P. on dispersed charcoal from the Square Hearth stratigraphic pit
and 1770 ± 60 B.P. from a wood charcoal within a pit structure cut into this unit at
the Santa Cruz Bend site appear too young.
Additional Evidence Supporting Radiocarbon Date Rejection
The similarity of sedimentary properties and elevational data from the two
stratigraphic pits and the riverbank indicate that Huckell's correlation of stratigraphic
units is in proper position. Furthermore, the sediments documented tend to indicate
vertical accretion of floodplain sediments (Huckell, pers. comm. 1997), rather than
accumulation in a paleochannel. Combined with the potential for intrusion of younger
charred material into older units through bioturbation or other means, these data
support rejection of radiocarbon dates as indicated by Huckell (1996a). A diagram of
Huckell's correlation of geologic units is presented in Figure 5.2.
Alternative Interpretation of Santa Cruz Bend Stratigraphy
An alternative interpretation of the stratigraphy at the Santa Cruz Bend and
Square Hearth sites is supported by acceptance of the radiocarbon dates and somewhat
different view of interpretation of sedimentary and soil characteristics. This
interpretation holds radiocarbon age estimates more important than elevational data,
particularly across a 950 m stretch of floodplain.
ca. 150 m
ca. 800 m
2440 70 (Beta 87067)
N \ \ \ \ \
1770 60
2360 t 70 (Beta 81057)
(Beta 80152)
Untt 5
Érn rj=
410 *60 (Beta 81049)
3600-260 (Beta117068) 3800*50 (Beta 810547
Watt 4
2290* 60 (Beta 81053)
1.1111111 .11
3740 *60
(Beta 81050r87089)
r. en, • r•
UNt 1
VZ •
qe55ij ec;:ip.•
.0 .. • • I.
Figure 5.2. Generalized stratigraphic columns at the Santa Cruz Bend and Square Hearth sites, showing inferred correlation of stratigraphic units by Huckell
Floodplains accrete sediments in a generally conformable manner on top of
older surfaces which may or may not be flat. These older surfaces may represent the
filled thalwegs of paleochannels, the near-bank margins or the outer margins of former
floodplains, abandoned meander scars, or filled lateral arroyos. Therefore, the
floodplain itself may not be flat during certain periods of time. Often floodplain
surfaces will slope toward the channel present at that particular time. The floodplain
will also tend to slope downstream, conforming roughly to the slope of the channel
(though not necessarily at exactly the same angle).
Because the sample of examined sediments within the floodplain is so small,
this alternate explanation focuses on the radiocarbon dates first, with some
consideration for the sedimentology and soil formation within the deposits, and then
attempts to find a geologic explanation for the radiometrically-dated succession of
sediments found in different parts of the floodplain. It should be noted that channel
deposits were not found in any of the profiles above the upper portion of unit 2 and
below unit 5. Therefore, all profiles exhibit sedimentation within the floodplain.
Former channels are expected to be either washed away in the present thalweg or
somewhere to the east of the present thalweg.
This alternate explanation acknowledges that Huckell's (1996) unit 2 appears to
be traceable across all profiles. The exhibition of characteristics typical of an arkosic
origin of the sediments and soil formation on this unit in both of the stratigraphic pits
suggests that these two units are, indeed equivalent in age. The problem then remains
that a date from the channel wall profile in unit 3 of 4610 ± 50 exceeds a date on unit
2 of 4380 ± 60 by several hundred years. The clay B-horizon present in the
stratigraphie pits is apparently missing in the upper portion of unit 2 in the riverbank
profile while a series of pedogenically-altered clay bands are present unit 3 in the
riverbank profile, but not documented in either stratigraphic pit. Huckell (1996a)
interprets the missing clay B-horizon in the riverbank profile as the product of erosion.
In a similar vein, Huckell (1996a) has proposed that pedogenically-altered clay bands
in the riverbank profile are a product of overbank deposition, while clay missing in the
stratigraphie pits is unaccounted for. Since there was apparently no erosion of the unit
3 paleosol in the stratigraphic pits, one must assume that the absence of these clayey
sediments in the stratigraphic pits is a product of non-deposition, rather than erosion.
While this is a possibility, an alternate explanation can be derived that accounts for
both the radiocarbon record and the stratigraphic sequence of sediments in the
riverbank profile.
This alternate explanation places the second band of clay sediments in the
riverbank profile (unit 3) within the upper portion of unit 2 in the stratigraphic pits,
forming a compound soil on unit 2 in the stratigraphic pits; notation of a compound
soil is shown in Huckell's figures of the stratigraphic pit profiles. The lack of a strong
hiatus between unit 2 and unit 3 in the riverbank profile is perhaps better explained
under this interpretation. Although soil formation is present in unit 2, sedimentation
continues, virtually uninterrupted throughout unit 3 at the riverbank and is followed by
a second episode of soil formation. Under this interpretation, sedimentation in the
stratigraphie pits continues following erosion and soil formation at the top of unit 2;
this episode of sedimentation is considered equivalent to unit 4 deposition along the
The remainder of the radiocarbon dated strata fall in line with the possible
exception that Huckell (1996a) segregates clay bands found above unit 3 in all profiles
from unit 3 and that he also assigns clay bands found in the riverbank profile to unit
5. It seems possible that the series of clay bands and silt units in the riverbank
profile, including the two charcos, might correlate with the lower set of clay bands in
the Square Hearth stratigraphic pit, thereby explaining the older age on this first clay
band. This alternate explanation is presented in Figure 5.3. Re-ordering of the
radiocarbon dates according to this alternate stratigraphic interpretation is presented in
Table 5.2.
Additional Evidence for Alternate Interpretation
In the fall of 1995, I had the opportunity to examine a pit for a pipeline
underlying part of new construction associated with Interstate 10 east of the riverbank
profile and south of the Santa Cruz Bend stratigraphie pit. The first observation
recorded from this pit is that the gravels and sands near the bottom of the pit did not
exhibit the heavy cementation found in cobble gravels along the riverbank profile,
suggesting that the cobbles found in the riverbank, which may be Pleistocene in origin,
are unrelated to the cobbles found in the bottom of the stratigraphie pits, which may
be Holocene in origin. There are also a greater number of soils and sedimentary units
found in this profile than were exhibited in any of the stratigraphie pits, indicating that
ca. 150 m
ca. 800 m
2440 t 70 (Beta 87067)
2360 t 70 (Bata 81057)
1770 a 60 (Beta 80152)
2290 *60 (Beta 81053)
3740 a 60
(1?ata 81050, 87069)/
4610 50 (Bata 81056).
'MT3U 3
0* • :**
• OL' elo,
VC?•••-ce - t.
4%' ...o .o.0 : ° ;?*(1.•:o‘P *9 -• P °693
Figure 5.3. Generalized stratigraphic columns at the Santa Cruz Bend and Square Hearth sites, showing alternate interpretation of correlation between
stratigraphic units.
some of those units have either been eroded in the other profiles or have formed
compound soils.
Table 5.2.
Alternate division of alluvial stratigraphic units at the Santa Cruz
Bend and Square Hearth sites.
Riverbank Profile
Strat. pit
1770 ± 60 (Beta 80152)
410 ± 60 (Beta 81049)*
2360 ± 70 (Beta 81057)
2440 ± 70 (Beta 87067)
AA: 12:745
Strat. pit
2290 ± 60 (Beta 81053)*
3800 ± 50 (Beta 81054)
3830 ± 60 (Beta 81047)
3600 ± 60 (Beta 87068)
3740 ± 60 (Beta 81050)
3740 ± 60 (Beta 87069)
4610 ± 50 (Beta 81056)
4380 ± 60 (Beta 81048)
Asterisks denote date considered questionable (*) or probably in error (**). All
dates are uncorrected AMS assays on wood charcoal. Radiocarbon date shown
in unit 3 in the AA:12:745 strat. pit is actually within a compound soil formed
from units 2 and 3, and is at the top of the unit therefore in unit 3.
Sediments Revealed in Juhan Park Archaeological Testing
The Juhan Park site is located on a surface defined by the Arizona Geologic
Survey (Jackson 1989; McKittrick 1988) as Qt3 (the Jaynes or Pleistocene terrace).
Although some of the sediments revealed during archaeological testing displayed
weakly developed carbonate accumulation in the form of fine filaments, the
carbonate accumulation does not appear to be sufficiently developed to support a
Pleistocene age. Clay present in some sedimentary units is due to sedimentation,
rather than post-depositional alteration and no other attributes of soil development
were present that would support a Pleistocene age for the sediments uncovered
during testing. Therefore, the entire exposed section of project area is Holocene in
age. In fact, the presence of discontinuous carbonate filaments and weak carbonate
coatings suggest that the sediments are only 1,000 to 2,000 years old (Gile 1975).
The southern and western portions of the project area are situated on a small
rise which slopes abruptly to the north and east toward the Santa Cruz River.
Although some of the slope at the northern end of the project area is natural, the
surface has been significantly modified by modern human activity. A large deposit
of trash located in the northern and eastern portions of the project area covers what
was probably the natural cut of the channel around the turn of the century.
Sediments underlying the trash deposit in this area (and exposed in trenches 5, 6, 7,
8, and 9; Figure 5.4) are composed of a massive homogeneous deposit of fine sand
and silt. A massive deposit of sterile fill sediment has been placed on top of the
high portion of the property to the south and west, possibly in an effort to level the
surface for construction of the industrial park to the south. These sterile sediments
cover Holocene alluvium of the Santa Cruz River which contain buried features and
artifacts: Additional buried features are found in preserved Holocene sediments near
the base of this rise (in the vicinity of trench 3; Figure 5.4).
Sediments revealed in test trenches and in the exposed walls of the channel
nearby are comprised predominantly of fine- to medium- grained deposits of Santa
Page 193
AZ AA:12:44 (ASM)
contour interval — 1 foot
50 m
200 ft
Computer cartography by
GEO—MAP, Inc. 1996
trash concentration
dirt rood
existing chain link fence
..... proposed chain link fence
proposed site development
.............. „
Figure 5.4 Location of excavated trenches at the Juhan Park site
modem building
area to be
archaeologically monitored
Cruz River alluvium. Although a large portion of the sediments is silt and clay
deposits that represent slow-moving overbank and slackwater deposits, some fine-to
medium-grained sand deposits were also present; these were probably deposited by
either small tributary or auxiliary channels of the river. The natural channel cut
which forms the slope of the property and the sequence of deposits located within
the walls of today's Santa Cruz River channel (to the northwest) indicate that much
of the property is located near the former channel of the Santa Cruz.
The Juhan Park Profile
In order to complement the archaeological testing conducted at Juhan Park
and to further investigate the exposure of sediments along the left (Juhan) bank of
the river portions of the bank exposure along this stretch of the river were mapped.
Six locations were mapped extending over 600 m of bank exposure. Profile 1
(Figure 5.5) is located directly beneath the Juhan Park site test excavations. Profile
6 (Figure 5.6) is located at the northernmost portion of the exposed bank, just south
of the area marked by Arizona Geological Survey (Jackson 1989; McKittrick 1988)
as Qt 1. The exposure covers middle to late Holocene alluvium of the Santa Cruz
River and likely represents the margin of these channel deposits. The upper surface
across the entire bank exposure has been eroded by modern flooding, most obvious
near profile 6 where the upper soil horizon is truncated, forming a shallow saddle.
Unit 8: Gravel and historic trash, Qt1.
Unit 7: Brown sand, upper boundary has been
eroded and is truncated by unit 8.
Unit 6: Pale to medium brown slightly loamy
sand. Forms an abrupt, conformable
boundary with unit 7, above.
Unit 5b: Silt. Upper 40 cm contains abundant
calcium carbonate filaments. Forms
an abrupt conformable boundary with
unit 6 above.
Unit 5a: Silt and clay bands, overbank deposit.
Forms a clear to abrupt boundary with
unit 5b.
Unit 4: Dark brown clay. Forms an abrupt
boundary with unit 5a.
Unit 3b: Silt, grading upward to very fine sand.
Forms an abrupt boundary with unit 4.
Unit 3b: Silt, grading upward to very fine sand.
Forms an abrupt boundary with unit 4.
Approximately 20 m north of this
profile, this unit is conformably overlain
by the post-3900 B.P. channel.
Unit 3a: Silt and clay bands, overbank deposit.
Forms a clear boundary with unit 3b..
Unit 2b: Medium brown silty clay. Forms an
abrupt with unit 3a.
Unit 2a: Fine loamy sand. Forms a clear
boundary with unit 2b.
Unit 1: Hard gritty muddy silt, heavily
indurated with calcium carbonate.
Forms and abrupt, erosional boundary
with unit 2a.
Figure 5.5
Stratigraphic column for Juhan Park, profile 1.
Page 196
9 •
radiocarbon sample
radiocarbon dote
poorly developed poleosol
pea grovel and coarse sand
well developed poleosol
coarse sand and grovel
pebble grovel
clay bonds
pebble to cobbel gravel
fine sand
cobble gravel
10 m
50 ft
Digital cartography by GEO—MAP. Inc. 7997
numbers in bold represent elevation
medium sand
in meters above sea level (MASL)
vertical exaggeration — 2X
in meters along profile face
Figure 5.6
coarse sand
Juhon Pork profile 6. Inset is o higher resolution drawing of the bank
prior to bank failure which resulted in the retreat of the bank by 6 meters.
The inset shows the location of radiocarbon samples recovered prior to bank retreat.
Hand mapping was conducted at each profiled area from a level line. These
level-line profiles were connected by mapping the datum nails with an electronic
total station surveying instrument by Geo-Map, Inc (Tucson, AZ). Profiles were tied
together using a computer-generated graphics package and additional field research
was conducted to fill in any gaps or unknowns. Profiles 2-5 were not intensively
examined. The purpose of these intermediate profiles was to provide stratigraphic
evidence for the succession of geologic events occurring between profiles 1 and 6
Profile I
Profile 1 exhibits a series of Holocene soils representing former floodplains
of the Santa Cruz River. In places, overbank deposition remains on top of the soils
indicating that the post-erosional surface received some sedimentation after
abandonment of each surface. Historic trash and cobble gravel form an inset terrace
adjacent to this bank exposure.
Stratigraphy, Geochronology, and Correlation
The lowermost deposit (unit 1) is comprised of a silt, heavily indurated with
calcium carbonate. This unit is most likely equivalent to Huckell's (1996a) unit 1 or
intermediate between units 1 and 2. The amount of carbonate suggests that the
sediment is likely Pleistocene in age (Gile 1975), although carbonate formation can
be the result of groundwater infiltration.
Unit 2 is comprised of fine loamy sand, interrupted by a thin band of clay
and followed by a medium brown silt to silty clay. This sediment is probably
middle Holocene in age. The boundary between unit 2 and unit 1 represents the
abrupt boundary between late Pleistocene/early Holocene sediments and middle
Holocene floodplain deposits.
Unit 2 is overlain by unit 3, a series of silt and clay bands representing
overbank deposits of the Santa Cruz River, and a A second overbank deposit of silt,
grading upward to a very fine sand. Either unit 2 or unit 3 likely represent Huckell's
unit 2.
Unit 3 is comprised of a thick, dark brown clay. This unit appears to be
equivalent to Huckell's unit 3 in the two stratigraphic pits and the riverbank profile.
It is also equivalent to a series of channels documented in profile 6. Charcoal
recovered from a paleosol formed at the base of one of these channels yielded a
radiocarbon date of 3810 ± 60 (CAMS-33965). These channels are truncated on
both the north (profile 6) and south (profile 1) sides by a series of younger channels
comprising the channel component of unit 4.
Unit 4 is comprised of two silt and clay bands forming overbank deposits on
unit 3, followed by a fairly thick deposit of silt with a moderately well-developed
zone of carbonate forming the boundary between this deposit and overlying unit 5.
This unit is almost certainly the same deposit as is represented in Huckell's units 4
and 5. As stated previously, the channel component of this deposit, which is
obliquely cut by the current bank profile forms the sediments intermediate between
profile 1 and profile 6. The northern end of the channel is illustrated by the
unconformity at the southern edge of profile 6 (left side, Figure 5.6)
Unit 5 is comprised of a pale to medium brown slightly loamy sand. This
deposit appears to be eroded in Huckell's (1996a) profiles, but may represent a
portion of his unit 6. A fairly well-developed B-horizon, represented by the
downward movement of organic matter, is formed at the top of this unit. The upper
boundary of this soil is eroded and capped by a thin layer of gravel.
Unit 6 is comprised of a well-developed A to A/B horizon soil formed on a
silt. Historic or modern artifacts are located within this deposit, indicating that it
represents the accumulation of trash and sediment moved by recent natural or human
Profile 6
Profile 6 (Figure 5.6) represents the obliquely cut Middle Holocene channel
of the Santa Cruz River. It appears to be roughly equivalent in age to the lowermost
unit in the Los Pozos west side stratigraphic pit (see Chapter 6). The profile was
mapped twice by hand and once electronically. Unfortunately, bank failure occurred
due to undercutting of the bank by the channel thalweg during the summer and fall
thunderstorms, between each mapping period.
Stratigraphy, Geochronology and Correlation
Units A and B are sand and gravel deposits of the Santa Cruz River that are
at a minimum, middle Holocene in age. These deposits fine upward to unit C, a
series of channel sands. These sand and gravel deposits are truncated forming the
boundary between one set of channel deposits and the obliquely cut channel (Figure
Unit D is the fill of a middle Holocene channel. Two thin bands of clay,
forming a compound soil in places, line the bottom of the channel. The channel is
most likely obliquely cut, given the changes observed between hand-mapped and
electronically-mapped profiles. This channel and the clay bands are equivalent to
unit 3 of profile 1.
Unit D is conformably overlain by sands (unit E, unit 4 of profile 1). These
sands form the near channel floodplain deposits, while the intermediary sand and
gravel sediments located south of profile 6 represent the channel itself.
Unit F is the uppermost sediment represented in this profile. It is equivalent
to unit 5 of profile 1. The upper portion of this sand and silt is eroded forming a
shallow saddle on which ceramic period artifacts are found.
The Juhan Park/Santa Cruz Bend reach of the river exhibits a record of
floodplain and near-margin sediments of the Santa Cruz River during the middle to
late Holocene. Their poor correlation in some parts of the project area demonstrate
the variability that can be represented by floodplain sediments that may form on
uneven surfaces and the difficulties in interpreting the differences between
depositional facies when the topography of the river and its paleochannels are not
Sediments younger than approximately 1700 B.P. are poorly represented in
any part of the profile. Channel sediments represented in the left bank profile are
obliquely cut indicating that at least a portion of the late Holocene channel was near
the current channel thalweg. The middle Holocene channel is probably represented
elsewhere and may have been partially removed by the current channel.
Because of the close proximity to Los Pozos, the floodplain sediments
provide further information that can be utilized when interpreting the channel and
floodplain sediments there and that are explored further in the next chapter.
1. For additional detail, consult the original report (Huckell 1996a).
The excavation of a multiple-component Middle Archaic and Early Agricultural
period site along the floodplain of the Santa Cruz River has presented an opportunity
to explore the period spanning the shift from hunting and gathering to agriculture.
Two exposures of middle Holocene alluvium provide indirect evidence of the
environments surrounding the river during these two periods. Correlation between the
geoarchaeological stratigraphy found at this site and excavations in other portions of
the Tucson Basin allow us to explore desert stream processes and the effects those
processes had on prehistoric settlement, subsistence, and site preservation.
The purpose of this chapter is not only to place the Los Pozos deposits in their
stratigraphic, geomorphic, and geochronologic context, but also to assess the
prehistoric behavior of the river in relation to its known historic behavior. As an
analog, historic situations are not always appropriate for evaluating the prehistoric
behavior of a river. However, by combining historic records with the known
dynamics of desert streams, the nature and regularity of streamflow can be assessed,
providing additional information about the environment in which prehistoric people
The Los Pozos site (AZ AA:12:91) is located on the Holocene floodplain (Qt2)
east of the Santa Cruz River between Prince and Ruthrauff roads within the City of
Tucson (Figure 6.1). A number of Late Archaic projectile points were discovered on
the site surface by an amateur archaeologist in the late 1940s (Morris 1951). Since
that time, additional archaeological surveys (Fritz 1974) and inspection of remains
found in berms and trenches excavated for activities associated with the Roger Road
Sewage Treatment Plant (Huckell 1992) have yielded abundant evidence of prehistoric
and historic cultural resources.
During investigation of a trench excavated by an employee of the Treatment
Plant in 1978, archaeologists working at the Arizona State Museum recorded a Late
Archaic pit structure and burial preserved 40 to 50 cm below the ground surface.
Wood charcoal from the pit structure yielded a radiocarbon date of 1780 ± 80 B.P. In
1991, additional bone fragments and teeth of a juvenile human were discovered near
this location. Excavation of these remains demonstrated that they were located in
secondary context. Samples of carbonized maize and charred wood from a charcoal
lens were found about 2.5 m below the surface in a river channel deposit; the wood
yielded a radiocarbon date 3230 ± 70 B.P. and the maize date was a few hundred
years younger (Bruce Huckell, personal communication 1997). While not associated
with any artifacts, the maize date is one of the oldest indications of agriculture in the
American Southwest.
Investigations of the portion of the site within the Interstate 10 corridor were
carried out in 1995 by Desert Archaeology, Inc. (Tucson, Arizona). On the west side
of the freeway, portions of 42 pit structures dating to the Early Agricultural period
were uncovered. On the east side of the freeway, a small Middle Archaic component
was excavated. The two components are separated stratigraphically by several units of
overbank deposition and horizontally by the interstate.
The Middle Archaic Component
The Middle Archaic component was restricted to a small strip of excavated
area of roughly 400 m 2 and consists of a number of small pit features, flaked stone
tools, ground stone implements, and botanical and faunal remains. Although few
Middle Archaic archaeological resources were discovered in trenches beyond the
boundary of the site, Middle Archaic features are often small and difficult to find.
Therefore, the site may extend beyond the boundaries of the excavated area, but is
obviously much smaller in size than later, Early Agricultural period sites.
Archaeological resources at the site were found in a silty clay alluvial unit
representing overbank and slackwater deposits of the Santa Cruz River and dating
around 3800 B.P. (see Table 6.1). Projectile points found at the site include both
Pinto (n = 4) and Cortaro (n = 14) styles as well as several other unattributable
fragments. The Cortaro point is considered by Sliva (1997) to be an expedient point
form. Although the Pinto and Cortaro point types appear to differentiate themselves
spatially and stratigraphically, secure radiocarbon dating places the Cortaro-style
projectile point in the Middle Archaic period. The spatial and stratigraphic
distributions of raw material sources suggest that at least two groups occupied the site
and that these groups exploited different raw material sources. Other evidence from
the flaked stone indicates that activities at the site included toolkit maintenance and
Table 6.1.
Radiocarbon dates from the Middle Archaic component at Los Pozos (after Gregory
Sample Context
culture bearing
natural stratum
wood charcoal
C14 Age
3700 +/- 70
culture bearing
natural stratum
wood charcoal
3820 +/- 70
extramural pit
wood charcoal
3820 +/- 80
culture bearing
natural stratum
wood charcoal
3880 +/- 100
extramural pit
wood charcoal
3900 +/- 80
culture bearing
natural stratum
wood charcoal
3950 +/- 100
extramural pit
wood charcoal
4250 +/- 60
Flaked stone analysis indicates that the site was a short-term hunting or
"gearing-up" area, where flaked stone tools were maintained or repaired. On the basis
of both the exotic origin of much of the flaked stone found at the site, and the
incongruity between raw material used in tools and debitage, Sliva (1997) infers that
the site was used episodically by logistic groups of hunters. The faunal data support
this argument, as do botanical and ground stone data. Fauna found at the site
represent species that could have been obtained nearby. Although W6cherl (1997)
attributes a relatively high artiodactyl count (compared to other Middle Archaic sites)
to subsistence choice, no other excavated Middle Archaic site yielding a substantial
sample of faunal remains has been located in such an environmental setting. The
nearest approximations are sites in small ephemeral drainages such as the Harquahalla
Valley. It is possible, therefore, that the environment created by the Santa Cruz River
in this particular locale was favorable for both humans and their large artiodactyl prey.
Additional bone tools were recovered, including three awl fragments, the tip of
a bone flaker, and three indeterminate worked bone implements. Ground stone was
infrequent, but not inconsistent in form with other Middle Archaic assemblages. One
whole mano, two mano fragments, and three indeterminate fragments were found
together with a single basin metate that had been destroyed by chipping a large hole in
the bottom. Both bone and ground stone implements exhibited restricted distribution
in the excavated area, and flaked stone debitage, including microdebitage, appeared to
cluster around features, suggesting that the distribution of tools may represent work
areas utilized by the different groups exploiting the site (Gregory 1997).
Paleobotanical evidence was typical of a riverine grassland. Plants that are
indicators of disturbance have a high ubiquity (Diehl 1997). Occasional trees, such as
cottonwood or mesquite, may have been present nearby. A single maize cupule was
recovered from the Middle Archaic context. The flowering period of plant taxa
represented at the site indicates that occupation of the site is most likely placed
between September and November, although a possible May-June occupation may also
be likely. As is typical with many floodplain sites, palynological sampling
unfortunately yielded little information.
The Early Agricultural Period Component
The Late Archaic settlement of the Los Pozos site is typical of other Early
Agricultural/Early Ceramic period settlements in the Santa Cruz floodplain. It consists
of numerous pit structures and extramural pit features. Radiocarbon dates on the
Early Agricultural period component have produced an average age estimate of 2097 ±
15 B.P.' (Table 6.2), falling on the late end of the Cienega phase.
The report on the Early Agricultural period component has not yet been
finalized; however, preliminary analyses indicate that the site is very similar to other
Early Agricultural period sites on the floodplain of the Santa Cruz River and
comparable to the Santa Cruz Bend site (AZ AA: 12:746) in terms of size and age.
The exposed portion of the site covers a 5,200 m 2 area and consists of a linear
right-of-way excavated along the west side of Interstate 10. The site is expected to
cover the entire area between the Santa Cruz River and the interstate and between
Sweetwater and Ruthrauff roads. The Wetlands site (AZ AA: 12:90) may be an
extension of the Early Agricultural period Los Pozos site, representing an extramural
activity area, or it may be a separate site.
Table 6.2.
Radiocarbon dates from the Early Agricultural component at Los Pozos (after Gregory
Dated a
"C Age
burned structural elements
grass stems
1940 +/- 60
intramural pit fill
mesquite (?) seed
1980 +/- 60
intramural pit fill
mesquite pod
2020 +/- 50
intramural pit fill*
maize cupule
2050+/- 50
pit structure fill*
maize cupule
2060 +/- 80
pit structure fill*
maize cupule
2090 +/- 60
intramural pit fill*
maize cupule
2090 +/- 80
intramural pit fill*
maize cupule
2110 +/- 50
pit structure fill*
maize kernel
2110 +/- 80
intramural pit fill*
maize cupule
2120 +/- 60
pit structure fill*
maize cupule
2140 +/- 60
pit structure fill*
maize cupule
burned structural elements
grass stems
intramural pit fill*
2140 +/- 50
2150 +/- 50
maize cupule
2150 +/- 50
intramural pit fill*
maize cupule
2150 +/- 60
pit structure fill*
maize cupule
2150 +/- 80
intramural pit fill*
maize cupule
2170 +/- 60
intramural pit fill*
maize cupule
2190 +/- 80
intramural pit fill*
maize cupule
2240 +/- 60
a All samples dated by AMS analysis.
* Material recovered from flotation samples.
Wetlands Site
First identified during a 1973 survey (Fritz 1974), an undisturbed, 50-m-long, 18cm-thick archaeological deposit was found at a depth of about 40 cm below the
disturbed ground surface during later subsurface testing (Kinkade and Fritz 1975).
Artifacts in this deposit included ground stone metate fragments; flaked stone
projectile points (including a Late Archaic point), cores, a drill, plain ware pottery
sherds, and decorated sherds identified as Tanque Verde Red-on-brown, Gila
Polychrome, and Papago red ware. Segments of possible prehistoric canals were also
found at a depth of about 40 cm. A historic canal and the adobe foundations of a
historic homestead occupied between 1911 and 1913 were also found. The northern
part of the site lay in plowed cotton fields, the middle section was disturbed by the
excavation of a wastewater canal, and the south end had been extensively graded for
irrigation. Along a high berm covering the sewage pipe, charred human bones, lithic
debitage, shell artifacts, sherds, heat fractured rocks, and ashy soil were found during a
1976 survey (Betancourt 1978). Archaeological testing was conducted in 1986 by
Desert Archaeology, Inc. (then the Tucson branch of the Institute for American
Research). Six prehistoric pits filled with fire-cracked rocks, charred wood, stone
flakes, and plain ware sherds were found between .5 and 1 m below the surface
(Bernard-Shaw 1986). Two historic canals were also found.
Recent excavation by the author (Freeman 1997) revealed a cluster of Early
Agricultural pits in a formal extramural area (Figure 6.2). Near the center of the
cluster was a large ground stone cache containing two manos, three metates, two
S.,'771 ;NG
5' 77 7 INC:
limit of
Oackhoe trench
pithouse or pit structure
AZ AA:12: 90 (ASA4)
50 ri
200 ft
Computer cartography by
CEO—MAP. Inc. 1996
Figure 6.2. Map of Wetlands site archaeological excavations. Burials are indicated
by solid black dots.
pestles, a stone ball, and a netherstone (Adams 1997). The cache may have been left
and intended for future use (Freeman 1997) or may have been part of a burial ritual,
which Mabry (1996a,b) has argued is the extension of a Middle to Late Archaic
pattern of cairn burials. Several pit structures, including one large, possibly
ceremonial, structure were also discovered in the area. Analysis of the material
remains from the site are currently under investigation, but preliminary analyses
suggest that maize was a dominant part of the diet. In addition to maize,
paleobotanical remains indicate that plants with the highest ubiquity values (frequency
of contexts in which a taxon is present) are Chenopodium/Amaranthus (.73), Prosopis
(.43), Camegia (.3), Gramineae (.3), and Echinocereus (.23)(Diehl 1997). Interpreting
the significance of these ubiquity values is difficult. Both Chenopodium and
Amaranthus thrive in disturbance contexts, but the seeds may also be ground into meal
and consumed (Adams 1988). Furthermore, the differences in ubiquity values between
plant taxa are dependent on whether plants were used and on the ways in which plants
were processed, used, and disposed of. With the exception of a single date of 2790 ±
50 B.P. on a San Pedro phase pit structure, the radiocarbon dates on the pit features
cluster between 2400 and 2500 B.P. (Table 6.3). Radiocarbon dates from the
Wetlands site place it at the early portion of the Cienega phase, suggesting that it may
indeed be a separate site from the Los Pozos component. The pit cluster was later
reused as a cemetery during the Early Agricultural period.
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Two large exposures of middle to late Holocene alluvium (Qt2) were excavated
on the west and east sides of the Interstate 10 corridor. The east-side excavation
exposed the Middle Archaic archaeological component. Trenches were placed
adjacent to the stripped area in order to expose additional geologic and archaeological
features which were present beneath the known Middle Archaic component. Sketch
profiles were drawn of all trench walls as well as the vertical walls of the stripped
area (Figure 6.3, see Appendix B for descriptions). The west-side stratigraphic trench
was excavated in three tiers to expose a series of Santa Cruz River channels to a depth
of 6.5 m. The vertical faces of the south side of this stratigraphic trench were mapped
in detail (Figure 6.4, located in the map packet). Additional detail on bedding and
other sedimentological features was derived from evidence in the east and north walls
of the stratigraphic pit and included in field notes. Geologic features were described
in detail using a combination of USDA and Folk classification systems (Folk 1954,
1974; Soil Conservation Service 1951; 1975). Descriptions for Figure 6.4 are found in
Appendix C. Radiocarbon samples were recovered and assayed where possible.
Excavation of two areas (Figure 6.1, see also Figure 1.2) provided the opportunity
to observe geologic features within two separate contexts. The east side excavation
provided a deep exposure of alluvial sediments forming the prehistoric floodplain of
the Santa Cruz River. Archaeological materials dating from the Middle Archaic
Page 215
burned vegetation
(similar to F918)
trench bottom
Scale: 1=3 meters
Vertical exaggeration — 2X
Cross—sections perpendicular to Trench 12 are schematic
and not in true perspective. They do, however, accurately reflect the
stratigraphic relationships revealed in the respective exposures.
trench bottom
Surveying and digital cartography by GEO—MAP, Inc., Tucson, Arizona 1997
N 1060
N 1050
N 1090
N 1080
N 1070
un excavated
drainage trench
fine gravel
medium gravel
burned clay
poorly developed paleosol
Figure 6.3 Profile of east side excavation
well developed paleosol
through the Early Agricultural periods were found within these sediments. The west
side stratigraphic trench provided a record of several former channels and channel
margins of the Santa Cruz River, dating from the Middle Archaic through the historic
periods. The two areas represent different facies of the same sequence, and used in
tandem they can reveal much about the nature of prehistoric channel change.
West Side Stratigraphie Trench
The 6.5 m deep west side stratigraphic trench provided an exposure of several
incisions and minor channels of the Santa Cruz River (Figure 6.4). Although not all
channel incisions were as severe as the historic incision of the river, the alluvial
stratigraphy provides a record of severe erosion as well as a general trend toward net
aggradation during the Holocene. The generalized stratigraphy of the west side
stratigraphic trench is represented in Figure 6.5.
Unit I
Sedimentation within unit I represents an upwardly fining sequence of alluvial
materials beginning with sands and gravels deposited in channel bars and the former
stream thalweg to a series of fine-grained silt and clay bands, representing overbank
and slackwater deposits associated with a shift in the channel (unit 2). Subunit Ta
(Figure 6.5) is comprised predominantly of small to medium cobble gravel and
medium- to coarse-grained sands exhibiting features typical of channel bar deposits
(Figure 6.4, deposits 1-5) and consistent with the modem bedload of the Santa Cruz
River. The basal portion of this subunit was probably entrained during flood events.
As the channel aggraded, the river could no longer transport the heavier deposits. As it
did so, it accumulated and stored these coarse deposits in channel bars. Although the
base of this channel was not recovered in excavation of the stratigraphic pit, this
subunit is probably close to the base of the channel. A radiocarbon date of 3990 ± 60
B.P. (CAMS 33961, Table 6.4) was obtained from a fragment of charcoal within the
upper portion of this subunit. This charcoal may have been washed in from the
Middle Archaic surface, presumably located to the east and possibly recognizable in
the bottom of trenches 90-92.
Table 6.4.
Additional radiocarbon dates.
(5 13 C
CAMS-33961 Unit Ia-top channel alluvium wood charcoal
-25.0 %o
CAMS-34923 Deposit 510 overbank alluvium maize cupule
-10.0 %o
CAMS-34924 Deposit 506 Feature 901 maize cupule
-10.0 %o
Sample No.
Sample Context
Material Dated
Samples prepared and age estimates provided by INSTAAR-Laboratory for Radiocarbon Research,
University of Colorado. Measured radiocarbon content run at Lawrence Livermore Laboratory for AMS
tSample contained sufficient mass to measure 4513C. These gasses are currently being run.
*Sample did not contain enough mass to measure . The (5 I3C reported for this sample is based on an
estimated value of approximately -10 per mil, typical of the values expressed by maize in other contexts.
Subunit lb is comprised of a few coarse-grained materials, but predominantly
finer-grained deposits (Figure 6.4, deposits 6-8). This subunit exhibits features typical
of the upper flow regime. This subunit is followed by deposition of very fine-grained
silts and clay (subunit Ic) typical of overbank or slackwater sedimentation (Figure 6.4,
deposits 9a-9d). The channel appears to have incised to a depth of at least 3 m below
the former floodplain and shifted slightly to the west during and after deposition of
this subunit. An inceptisol is formed on the upper boundary of this subunit and may
represent a grassy swale present near the thalweg. A more organic surface horizon is
missing at the upper boundary of this deposit, indicating that portions of the floodplain
sediments near the former channel were removed by erosion.
Unit II
Sedimentation within unit H includes both channel and a floodplain facies, which
can be correlated laterally across the profile. The bottommost portion of this channel
was not reached by backhoe excavation, but appears to have incised at least 3 m
below the former floodplain. Apart from the lowermost gravel, subunit Ha (channel
fill) appears to represent the upper portion of the flow regime. Sand and gravel
deposits in subunit Ha are similar to deposits at the base of subunit Ia; however, the
gravel is finer-grained, composed of generally small cobble to pebble gravel and
indicating that the stream experienced diminishing competence over time. Sediments
in the upper portion of subunit Ha vary from very coarse to very fine. The channel,
although truncated by subsequent periods of erosion, appears to be parabolic and is
wider than it is deep.
The floodplain facies of subunit Ha is comprised of a massive medium sand with
some weak horizontal laminae (Figure 6.4, deposit 10). This facies represents an
episode of overbank flooding and is capped by a very thin carbonate band which can
be traced into the channel facies (Figure 6.4, deposit 11). Subunit IIb is comprised of
a fine- to medium-grained finely-laminated sand (Figure 6.4, deposit 12). This deposit
contains laminae of magnetite (placer deposits) and displays very fine low-angle
trough cross bedding. The deposit represents a minor channel fill and overbank
deposits. An entisol is formed at the top of the deposit, indicated by bioturbation and
some carbonate accumulation. The boundary between unit II and overlying unit III is
marked by a slight depositional hiatus (diastem) and a very minor erosional
Unit III
Unit III is comprised of a series of overbank and slackwater deposits which fill a
minor channel formed at the unit II/III boundary. Subunit IIIa is comprised of a
massive silt with strong carbonate accumulation (Figure 6.4, deposit 13). A
depositional hiatus between subunits Ma and IIIb and the accumulation of carbonate
filaments may be pedogenic, but could also be derived from groundwater. This hiatus
is followed by deposition of very fine-grained silt and clay bands of subunit IIIb.
These bands are found both in channel fill and overbank facies (Figure 6.4, deposits
14 and 15). A radiocarbon sample was recovered from the base of deposit 14 (subunit
IIIb) but not assayed.
On the basis of correlation with trenches to the east and south of the stratigraphic
pit, it is probable that unit III is the Early Agricultural period floodplain. Minor
episodes of soil formation may have been continuous throughout this deposit, and have
resulted in the translocation of younger sediments into the underlying silt. A very
abrupt non-depositional or possibly erosional unconformity forms the boundary
between subunits IIIb and Inc. Subunit IIIc is again comprised of a series of silt and
clay bands (Figure 6.4, deposit 16) followed by a single, massive silt (Figure 6.4,
deposit 17). These two deposits probably represent a soil formed during the Early
Agricultural period occupation of the Los Pozos site. The erosional unconformity at
the top of this sequence is marked by severe channel incision.
The channel filled by unit III sediments is clearly much shallower than previous
channels and also parabolic in form. Deposits within the channel facies of unit III are
as fine-grained as their floodplain components and represent a clear change in
streamflow conditions. Incision at the upper boundary of unit II was likely less than 1
m in depth and is followed by 2 m of aggrading sediments. After aggradation of the
unit III sediments, the channel experiences an incision greater than any in its Holocene
history and probably only equaled by incision during the late nineteenth century.
Unit IV
Though the bottom of the channel was not reached, incision following unit III was
probably at least 4 m below the former floodplain. Evidence for a vertical-walled
arroyo is present near the bottom of the exposed channel, as is evidence for
mass-wasting of the arroyo walls (Figure 6.4, subunit IVa, deposit 20d). Gleyed
well-sorted fine sands surrounded by concentric, circular clay rings at the bottom of
the stratigraphic pit and near the erosional boundary may mark the presence of a
spring conduit near the base of the channel. Soft sediment deformation characterizes
the sediments overlying the spring and may have been caused by sapping at the bank
Subunit IVb is comprised of channel bar and fill deposits. The lowermost portion
of this subunit is comprised of small- to medium-sized cobble gravels. The uppermost
gravels are imbricated. This unit is overlain by a series of sands, silts, and clays. A
floodplain facies of this deposit (Figure 6.4, subunit IVc, deposit 20) is characterized
by bands of silt and clay. The uppermost clay was very dark grayish brown in color
and contained numerous carbonate filaments. These characteristics are typical of an
organic A-horizon, and may be the result of a high water table or slackwater
deposition in the channel thalweg and subsequent soil formation. Abundant charcoal
is present in the floodplain facies as well as parts of the slumpblock.
Unit V
Unit V is characterized by several minor channels and channel fill episodes.
These channels were cut no more than 1.5 m below the former floodplain. The
channels are filled predominantly with coarse- to medium-grained sands and
occasional silt bands. A floodplain facies is recognizable in a small area near the
bank margin, but is incorporated into the plowzone to the east.
Unit VI
Unit VI is again comprised of minor channels and channel fill episodes. Again
the channels were cut no more than 1.5 m below the former floodplain. These
channels are also filled with coarse to medium sands and silt bands. The floodplain of
unit VI component is incorporated into the historic plowzone.
East Side Excavation
In contrast to the west-side stratigraphic pit, the east side excavation displays a
long sequence of overbank and slackwater deposits of the Santa Cruz River floodplain
(Figure 6.3). For the most part, erosional boundaries are recognizable only by
documentation of a weathered soil profile and correlation with known erosional
deposits in the west side stratigraphic pit. Less time was available to document the
northern portion of the excavated deposits, some of which appear to be older than the
southern portion of the excavation.
Deposits 533-537
Deposits 533-537 are located in the northern portion of the trench. This column
of sediments received less geologic attention than other parts of the excavation, due to
time constraints. The lowest deposit is a gravel (Figure 6.3, deposit 537). This gravel
did not exhibit the carbonate accumulation typical of Pleistocene gravels documented
elsewhere in the floodplain, but did display a reddish hue and accumulation of
secondary clays typical of other Pleistocene soils. It is possible, therefore, that these
gravels are late Pleistocene or early Holocene in age. Overlying the gravels were a
series of clays and silts, typical of overbank or slackwater deposits. Oxidized mineral
stains on these sediments are probably a result of capillary movement of groundwater.
These sediments are also probably early Holocene in age.
Channel deposit (520s) and Deposits 531-532
Deposit 533 is truncated by a channel filled predominantly with coarse- to
medium-grained sands and gravels. An overbank facies of this channel appears to
conformably overlie the previously discussed deposits. This channel is then cut by a
second minor channel (Figure 6.3, deposit 517), representing a braided middle
Holocene stream.
Deposits 514-517
Deposits 514-517 are located in the southern portion of the excavation area. The
majority of geologic attention on the east side was focused on two soil profiles in this
area, one of which forms a complete stratigraphic section with overlying deposits
501-509. Deposits 514-517 represent the fill of a low middle Holocene channel. The
lowermost portion of the channel fill is comprised of pale reddish brown matrix of
coarse sand surrounding very small- to medium-sized cobble gravels (Figure 6.3,
deposit 517). This deposit is overlain by a pale brown gravelly loam (Figure 6.3,
deposit 516). The pale brown gravelly loam is typical of slopewash deposits formed
by reworked bajada sediments. These slopewash sediments are overlain by a grayish
brown sandy clay with some fine pebble gravel (Figure 6.3, deposit 515), which is in
turn overlain by a series of silts and clays (Figure 6.3, deposit 514). In places deposit
514 is sandier.
Deposits 514-517 appear to be the fill of a low middle Holocene channel and shift
to floodplain overbank and slackwater deposition. As this near-margin channel was
filled, the thalweg shifted somewhere to the west of this profile and this location
became part of the floodplain. Soil formation can be observed at the upper boundary
of deposit 514, where color is a dark grayish brown and a moderate number of
carbonate filaments are present. The accumulation of oxides, carbonates, and very
dark grayish brown color in subunit 514c is likely a result of close proximity to
groundwater prehistorically during initiation of this sedimentary sequence.
Descriptions for these units in nearby trenches appear to represent the floodplain facies
of this sequence (G. Huckleberry field notes). Radiocarbon dates on cultural feature
917 (a feature of unknown use cut from deposit 515) support a middle Holocene age
for the deposit (Table 6.1, Beta-85204 and Beta-88147). A single radiocarbon date on
an in situ band of burned vegetation at the upper boundary of deposit 514 further
supports this middle Holocene age (Table 6.1, Beta-88143) around 4500 B.P.
(corrected, uncalibrated). The average of these three dates is 4471 ± 50 B.P. The
upper portion of this sequence of deposits may extend to the northern portion of the
trench (represented by deposit 531).
Deposits 512-513
Deposits 512-513 are located in the southern portion of the excavation area and
may be compressed into deposit 531 in the northern portion of the excavation. These
sediments represent a sequence of overbank siltation, followed by additional overbank
or slackwater deposition and soil formation. The same basic sedimentation pattern is
repeated throughout the remainder of the sequence.
Deposits 510-511
Deposits 510-511 are located in the southern portion of the excavation area and
are part of this repeated pattern of sedimentation occurring in previous deposits.
These sediments also extend to the northern portion of the excavation. Deposits
510-511 represent a sequence of overbank siltation, followed by additional overbank or
slackwater deposition and soil formation. Deposit 510 was the focus of most of the
archaeological excavation on the east side of I-10 and produced numerous flaked stone
artifacts as well as some animal bone. Four radiocarbon dates (Beta-81329, -88145,
-95633, and -95634) were derived from the dispersed charcoal in natural stratum
(Figure 6.3, deposit 510) from which Middle Archaic archaeological resources were
recovered, and three additional dates were recovered from charcoal in cultural features
within this natural stratum (Beta-88144, -88148, and -95635). The six youngest of
these dates can be combined for an average age of 3829 ± 35 B.P. (see Table 6.1,
corrected, uncalibrated) and confirm a middle Holocene age for these deposits. A
single corn cupule recovered from this natural stratum yielded an age estimate of 4050
± 50 B.P. (CAMS-34293, Table 6.4).
Deposit 510 is comprised of a series of laminated sedimentary deposits ranging
from a very dark grayish brown clay to grayish brown to light grayish brown silty clay
in the center of the deposit. The upper portion is again darker, indicating greater
organic content near the surface of the soil. Organic content at the base and top of the
soil and few, very fine oxides indicate close proximity to groundwater. Many fine
carbonate filaments and small nodules are also present in the soil. The upper surface
of the deposit has been eroded and weathered. The deposit is similar to cienega soils,
but appears to have received overbank sedimentation throughout its depositional
Deposits 502-509
These deposits were defined predominantly during archaeological testing and
observed in a single profile during excavation. Deposits 503 through 509 represent the
continuous, rapid sequence of overbank and slackwater sedimentation typical of
floodplain deposits. Although these deposits are roughly 1 m in total thickness, there
is little evidence for pedogenesis within this series of deposits and no strong erosional
hiatuses, apart from the hiatus at the top of deposit 510. A coarser-grained very fine
sand (Figure 6.3, deposit 507) within the sequence displayed low-angle trough
cross-bedding, typical of sedimentary structure that has been unmodified by
pedogenesis. Although this type of structure can be found in older sediments, the thin
nature of each deposit should exhibit pedogenetic activity if the deposit had been
continuously building up since ca. 3800 B.P. The weak, medium, angular blocky
structure displayed by the clayier sediments is probably due to the dry content rather
than pedogenetic alteration. Some weak to moderate carbonate accumulation is
present in deposits 505 through 509. A single radiocarbon date on a corn cupule
recovered from an archaeological feature in unit 506, yielded an age estimate of 1990
± 50 B.P. (CAMS-34294, Table 6.4), basically contemporaneous with the Early
Agricultural component on the west side of the interstate, averaging 2097 ± 15 B.P.
(Gregory and Baar, 1997; Table 6.2). This average represents 18 of 19 dates from the
Early Agricultural period of the site; a single date of 2240 ± 60 B.P. from the Early
Agricultural period component was not averageable.
Deposit 502 (Figure 6.3) represents a more slowly accumulating cienega-like
deposit. This deposit is darker in color than most of the clayier sediments in the
profile suggesting a higher percentage of organic matter. The lower portion of the
deposit is even darker in color than the upper portion of the deposit. A Hohokam
canal was found excavated into this deposit; however, Gregory and Baar (1997)
correlate this deposit with the Early Agricultural period occupation excavated on the
west side of Interstate 10.
Deposit 501
Deposit 501 (Figure 6.3) represents the accumulation of additional floodplain
deposits, most of which have been disturbed by historic plowing or other historic and
modern processes. Modern construction episodes are highly visible in parts of this
deposit near the interstate.
Correlation between deposits within and outside the Los Pozos site are necessary
to assess the geomorphology of the site area, the nature of stream dynamics and the
environment in which prehistoric people lived. Intersite correlation provides the
necessary background to examine the relationship between the stream and the
floodplain at a single locality, providing the environmental context of the project.
Intrasite correlation provides a broader perspective of how those individual
environments interrelate and whether the river responded to changes in the same
manner in each reach.
Intrasite Geochronology and Correlation
The lateral distribution of the east side excavation and the west side stratigraphic
pit across the project area must be correlated before attempting intersite correlation.
Because of the nature of facies relationships, certain deposits in the channel fills
cannot be directly related to a corresponding floodplain component. Floodplain
deposits typically demonstrate subtle changes across wide areas. Single bands of clay
will split or several will combine together to form a single band. Soils can be eroded
in one area and perfectly preserved in another. Because depositional facies of the
Santa Cruz River will exhibit varying lithologie and pedogenetic characteristics and
because floodplain deposits exhibit similar lithologic and pedogenetic characteristics,
chronostratigraphic correlation is emphasized. Secure stratigraphic correlation can
only be accomplished with numerous radiometric age estimates or diagnostic cultural
horizons if strata cannot be traced from one site to another. Deposits with distinct
pedogenic or sedimentary features can sometimes be used to support these correlations.
The series of clay bands at the upper portion of unit I (Figure 6.5, subunit Ic) in
the west side stratigraphic pit are probably slightly younger than deposit 510 (east
side) and probably represent a late middle Holocene or early late Holocene deposits.
A radiocarbon sample on dispersed charcoal from sands (upper subunit Ta) underlying
these clay and silt bands produced an age estimate of 3990 ± 60 B.P. (CAMS-33961)
and probably represents charcoal reworked from the middle Holocene deposit (deposit
510) exposed in trenches to the east of the west side stratigraphic pit (Figure 6.4).
Under this scheme, unit I represents a migration of the middle Holocene channel to the
west and incision after the middle Holocene occupation of the project area.
A series of deposits on the floodplain extending from the Early Agricultural
period excavation area to the west-side stratigraphic pit appears to correlate well with
the upper portion of unit III. Although radiometric evidence has not been used,
archaeological features in these floodplain deposits appear to satisfy independent
correlation between deposits of similar characteristics. Because subtle depositional
changes can occur over the short distance between trenches, secure correlation between
the excavated Early Agricultural component and deposits in the east-side excavation is
more difficult. Characteristics of the floodplain depositional regime during the Early
Agricultural occupation are found throughout deposits 502-509. The entire sequence
of overbank floodplain deposits (502-509) may represent the same sequence seen in
subunits Illb through Hid in the west-side stratigraphic pit. Alternately, floodplain
deposition during the Early Agricultural period may begin somewhere within the
sequence of sediments represented by deposits 502-509. The former hypothesis is
supported by radiometric evidence in unit 506. Aggradation rates, estimated below,
can be used as a rough gauge to support this hypothesis and the overall depositional
history of the floodplain.
Ag gradation Rates and the Estimated Age of Paleosols
Rough aggradation rates for similar channels have been calculated by Parker
(1995) based on cross sections of the San Xavier reach (Waters 1988). By applying
these aggradation rates to channels in the west-side stratigraphic pit, estimates of the
ages of deposits in the west-side stratigraphic pit can be proposed. Units III and IV of
Waters' (1988) report are the closest in age (although younger), size, and sedimentary
content to the middle to late Holocene channels represented in the west-side
stratigraphic pit. Estimates calculated for these channels were .68 and .4 cm/yr
respectively. Following the curvature of the channel, where present, a bottom depth of
each channel in the west-side stratigraphic pit was estimated. The oldest channel
represented was assumed to be close to its bottom depth, based on the size of cobble
clasts in the southeastern corner of the profile. A beginning date of approximately
3800 B.P. was attributed to the bottom of unit I based on charcoal found within the
unit and probably reworked from the adjacent bank deposit. The 3800 B.P. estimated
date is probably older than unit I and does not reflect intervening time between
deposition of the adjacent bank deposit and erosion of the paleochannel filled by unit I
sediments. However, the charcoal may have been produced (by either natural or
cultural agents) on that surface any time between final deposition of the adjacent bank
deposit and erosion of the paleochannel. The 3800 B.P. estimate is, therefore, a very
rough estimate and probably the maximum possible age for the base of the oldest
paleochannel. The upper surface of unit III was attributed to an age estimate of 2000
B.P. based on the average age of cultural materials found in the deposit as it extends
to the excavated site area.
Two methods were used to calculate the age estimates in Table 6.5. Beginning
with a date of 3800 B.P. on the bottom of unit I, estimated ages for the top of each
aggradational episode were calculated by subtracting the number of estimated years of
aggradation from the previous age. The slower aggradation rate provides the
minimum top age of the deposit and the faster aggradation rate provides the
maximum. Unit IV deposit ages were calculated using this method and a starting date
of ca. 2000 B.P. Retrograded estimates were calculated using the opposite method.
Beginning with a date of 2000 B.P. on the top of unit III, estimated ages for the
bottom of each incision were calculated by adding the number of estimated years of
aggradation from the previous age. The slower aggradation rate provides the
maximum age of the bottom of each deposit and the faster aggradation rate provides a
minimum age. Neither hiatuses, which are obviously present in the profile, nor
erosion of paleosols are accounted for in the age estimates. Also, it is important to
remember that the channel deposits represent only the last flow event and may have
experienced several decades of scour and fill prior to final deposition. Finally,
channel geometry and sedimentation have a great impact on the rate of aggradation
and probably have had the most significant impact on the aggradation rate used for
unit III. As a consequence, these estimated dates should be used only as a rough scale
from which to understand the sequence of deposition and develop testable models of
prehistoric floodplain use.
Table 6.5. Estimated age of stratigraphic units in the west side stratigraphic pit at Los Pozos (AZ AA:12:91).
min. age
max. age
max. age
min. age
(est. rcybp)
Given the age of the wood charcoal in subunit Ia, the maximum age estimates are
probably closer to the true age of the paleosol within this profile. Using these age
estimates, the series of clay bands within subunit Ic probably date to ca. 3,200-3,300
years ago and the clay bands within subunits Illb-d probably date between 2,700-2,500
and 2,000 years ago.
Calculation of aggradation rates for deposits in the east-side stratigraphic pit
would be unfounded, as deposition within a floodplain facies is dependent not only on
streamflow conditions but also on position of the channel relative to the documented
floodplain sequence and the differential potential for preservation of floodplain
sediments across the site. Larger floods and floods of channels close to the examined
profile would deposit greater concentrations of sediment, while floods that produced
less extensive overbank flows and in channels at greater distance from the profile may
not deposit sediments at the examined profile. The absence of strong hiatuses between
deposits 509 and 502 indicate that sedimentation within these units was relatively
continuous and rapid.
Intersite Geochronology and Correlation
Intersite correlation is usually quite difficult. The two most reliable methods of
correlating deposits across such a wide expanse are radiocarbon dating and associated
cultural materials. Using excavated and natural exposures, Haynes and Huckell (1986)
have attempted to correlate Holocene deposits of the Santa Cruz River from Pima
Mine Road to Ina Road. Most of their data focused on the area between Airport Wash
(just north of San Xavier) and Pima Mine Road. They relied predominantly on
radiocarbon dating and associated archaeological materials to establish correlations
between deposits separated by lengthy distances. Later, Huckell (1996) produced an
alluvial stratigraphy for deposits at the nearby Santa Cruz Bend site (AZ AA: 12:746,
ASM). For conformity with other excavations, the designations used by Haynes and
Huckell (1986) will be used here; however, some discussion of the relationship of this
excavation to excavations conducted in other parts of the Interstate 10 corridor will be
addressed using Huckell's (1996) report as well as additional data presented in chapter
Based on existing radiocarbon dates (Haynes and Huckell 1986), sediments in
deposit 514 of the east side excavation appear to be roughly equivalent in age to the
upper portion of Haynes and Huckell's unit B 1 . Sediments in deposit 510 (Figure 6.3)
are roughly equivalent in age to either the upper portion of unit B / or the lower
portion of
Deposits 503-509 are either equivalent in age to the upper portion of
unit B2 or the lower part of C I . Deposit 502 is roughly equivalent in age to the upper
portion of unit C I or unit C2.
The age estimates for older deposits in the east side excavation area (the 520 and
530 series deposits) are based on relationships to younger deposits and conjecture from
previous studies. Waters (1987, 1988) notes that the Santa Cruz River was a shallow,
braided stream prior to 8,000 years ago. He observes a hiatus between 7000 and 2500
B.P., however, evidence from Haynes and Huckell (1986) suggests that the hiatus only
lasted to roughly 4500 B.P. Waters (personal communication 1996) has suggested that
the discrepancy between his data and Haynes and Huckell (1986) may be due to
complex response. He notes that the ca. 4500 B.P. dates from Haynes and Huckell's
work are predominantly from slopewash deposits, and surmises that, in the San Xavier
area, the river was incising while at the same time at Ina Road, those entrained
sediments were being deposited and stored.
1989; Monger 1995), from palynology (Hall 1985), and from packrat middens
(Spaulding 1991) support the interpretation of this period as one of erosion and
drought conditions.
Around 5500 years ago, the Santa Cruz River began to aggrade, forming at first a
shallow, braided stream. The presence of abundant iron and manganese
oxides/hydroxides in units 514 through 517 of the east side excavation indicates a
resurgence of groundwater, absent in the 520 series deposits. The river was at this
time located closer to the margin of the Jaynes terrace (Qt3) and at least one of the
braids of that channel was present where excavations on the east side of the present
interstate were undertaken (520 deposits). Evidence appears to indicate a water table
relatively close to the surface. Again, in both the San Xavier and Los Pozos areas
slopewash forms at least a portion of this component. Based on the known patterns of
channel change in the Santa Cruz River, instrinsic factors do not appear to account for
channel changes around 5,000-4,500 years ago. An extrinsic factor, such as climate
change, seems a more likely cause of the change in stream competence that set the
Santa Cruz River on an aggradational trend. Because frontal and tropical moisture
produces large flood discharges in the Santa Catalina Mountains with enough energy
to continue downstream (see Chapter 3), tributary valleys of the Santa Cruz (e.g.,
Rillito Creek, Canada del Oro) and their points of confluence with the Santa Cruz
were most likely the first areas affected by changes in climate. The resulting
geomorphic changes in the relationship between the Santa Cruz River and its tributary
valleys signal that climatic change. The proximity of Los Pozos to Rillito Creek
enhanced the ability of this reach to store sediment. As it aggraded, the thalweg,
which was a single narrow and shallow channel, shifted to the west. The near absence
of deposition during this time period in other reaches of the Santa Cruz River is
probably due to the lag in response to changing climatic conditions.
Overbank flooding from each successive channel deposited a series of fine-grained
silts and clays on the floodplain. The first of these fine-grained materials was
deposited around 4,000 years ago and formed the context for the Middle Archaic
occupation on the east side of the interstate. Previous channels may be indicated by
the slope of overlying deposits conforming to depressions underlying them, possibly
exhibited in trenches intermediate between the east side excavation and the west side
stratigraphic pit (Figure 6.4).
Shortly after the Middle Archaic period occupation, the stream underwent incision
and the channel shifted to the west. Unfortunately, no datable samples were found at
the upper boundary of this aggradational episode, making it impossible to predict the
possible age of incision. This post-Middle Archaic incision was probably 3-3.5 m in
depth (unit I). After channel incision, the aggrading stream became increasingly less
competent until series of fine-grained silts and clays were deposited on the floodplain
(unit Ic). This may represent some kind of early Late Archaic/Early Agricultural
deposit and may have again been the setting of floodplain activities. A second
incision (this time to a depth of at least 3 m) followed, and the channel again shifted
westward. During these two periods of incision, the stream was underfit to its
channel. Floods in the channel rarely exceeded bankfull discharge and were not
extensive across the floodplain. However, particularly rich or attractive habitats may
have been locally available to populations utilizing the floodplain during short periods
at the end of each aggradational episode (represented by unit Ic in the west-side
stratigraphic pit).
One of these aggradational periods, followed by a minor depositional hiatus,
appears to form the context for the florescence of the Early Agricultural period
(probably between 2500 and 2000 B.P., see Gregory 1997). During this period, the
smaller size and depth of the channel allowed numerous extensive episodes of
overbank flooding. The floodplain was stable for a relatively lengthy period in which
early farmers comfortably made the transition to a more sedentary lifestyle (Gregory
A third, and this time the deepest (> 4 m) incision of the Santa Cruz River
followed this Early Agricultural period fluorescence. During this time, early farmers
may have accessed the water table by constructing wells like those found at both the
Los Pozos (Gregory 1997) and Sweetwater Wetlands sites (Freeman 1997). The
channel formed a steep-sided, almost vertical-walled arroyo, much like that created by
the historic incision of the river. This channel also aggraded over a several hundred
year period, during which time the river was again underfit to its channel and an even
less reliable source of water. Farmers in the Tucson Basin during this time must have
adapted new methods of farming, including ak-chin irrigation on the bajadas.
Aggradation of this underfit channel probably occurred until sometime between 1,340
and 875 estimated years ago (or roughly A.D. 600 to 1100) and is followed by minor
channel shifts until the historic period incision, which caused the channel to cut a
continuous trench to a depth of 10 m in some reaches.
Environmental Implications of Channel Changes
The trend toward net aggradation demonstrated by river alluvium after at least
4,500 years ago appears to be evidence for a long-term change in climate. The
increased effective precipitation noted after 5,500 years ago has been attributed to an
increase in monsoonal-type precipitation (Markgraf 1985). A high frequency of this
type of storm activity would be consistent with a trend toward aggradation. During
this aggradational trend of at least 2,500 years, episodes of severe degradation or
nondeposition also occurred. These degradational episodes are discontinuous through
the stream system and may have resulted from either short-term changes in the
frequency of different types of storms or response to intrinsic geomorphic factors.
Short-term changes in the types of storms can create perturbations in the
geomorphic system that result in intrinsic responses. For instance, the input or loss of
sediment at the confluence of tributary streams (i.e., Rillito Creek or Canada del Oro),
resulting from short-term changes in the frequency of tropical and frontal storms,
would potentially cause a perturbation in the trunk stream (i.e., the Santa Cruz) and
would require an adjustment in the behavior of the trunk stream. While the initial
perturbation was caused by an extrinsic factor (climate), the trunk stream would be
responding to an intrinsic factor (change in gradient).
An adjustment in the behavior of the reach of the Santa Cruz upstream (south) of
its confluence with Rillito Creek is particularly likely due to confinement of the valley
in this reach (see Chapter 3) and is highlighted by the discontinuous nature of channel
change reflected in this reach. A change in gradient might result in a series of
localized cutting and filling events that would migrate through this reach, but would
not form a continuously entrenched arroyo. These events are probably asynchronous
for at least short reaches, and are typified by incision, entrainment, and storage of
sediments in different parts of the same system.
During the period from 4500 to 2800 or 2500 B.P., the stream system was
characterized by complex response to perturbations created at the confluence of
tributary streams. In areas where sediment storage was the dominant process, local
microenvironments were created. Historic records suggest that these areas might have
formed local wet meadows (cienegas) or more extensive mesquite bosques and grassy
swales. The discontinuous nature of these microenvironments was altered after a short
period of non-deposition 2,800 to 2,500 years ago when the channel became a small
shallow drainage. During the Early Agricultural period (ca. 2800 or 2500 to 2000
B.P.) sediment storage and overbank deposition were dominant processes throughout
the focus reach, extending these microenvironments across a wide area.
It is difficult to say what processes dominated channel change along the river after
the Early Agricultural period. The west-side stratigraphic pit exposes a portion of the
record for this interval, but without more detailed information about the stream
behavior during the periods that followed the environmental implications of channel
change during this period is more sketchy.
Implications for Human Settlement and Site Preservation
The trend toward net aggradation created localized favorable riparian habitats that
migrated upstream as each reach of the river successively responded to this change.
By 4,000 years ago, a favorable localized environment was in place at the Los Pozos
site for Middle Archaic populations to exploit. As the stream responded to changes in
its system, the specific location of this favorable localized environment would have
migrated upstream and the location utilized by prehistoric occupants of the Los Pozos
site might have become less favorable for a period until it again became favorable
around 3,500 to 3,300 years ago. This pattern of incision and deposition continued for
approximately 1,500 years (until 2800 to 2500 B.P.), at which time a longer-term
favorable environment was created.
The dynamic processes of erosion and deposition continuing from the Middle
Archaic into Late Archaic times created a series of localized favorable habitats during
the Middle Archaic and Early Late Archaic/Early Agricultural periods. During this
time, settlement of the floodplain was restricted to local environmental niches which
progressively moved upstream over the course of several generations. By the
florescence of the Early Agricultural period (2,500-2,000 years ago), the floodplain
had attained greater stability. Though progression of these favorable niches probably
still occurred, there appears to have been a significant period, during which prehistoric
people could rely on a favorable floodplain environment conducive to the long-term
cultivation of plants.
Following the Early Agricultural period farmers were likely drawn away from the
river. A period of incision would have made the river a poor place for floodwater
farming. The few Early Ceramic period sites found in the floodplain appear to be
located slightly closer to the Pleistocene terrace. Certainly, by the Rillito phase, the
floodplain was a more reliable source of water once again.
The current model of floodplain development created by geoarchaeological
stratigraphers in the Santa Cruz Valley focuses on the apparent synchroneity of
geologic events (particularly incision) within the valley itself and across southern
Arizona (Haynes 1968); however, both the cause of incision and the synchroneity of
these events are the subject of much debate in fluvial geomorphology and climatology.
Furthermore, those models cannot account for the subsistence-level decisions employed
by human groups over periods of several generations. By employing Parker's (1995)
model that accounts for sedimentational and hydrologic controls on the river system,
the apparent synchroneity of geologic events and the subtle differences in depositional
history can be documented in different parts of the river.
These processes have a tremendous effect on the way in which prehistoric people
utilized the floodplain environment and on what resources may have been available for
them to exploit. The model also accounts for gaps in the archaeological record that
may be present in different reaches of the river or at different times. The Los Pozos
stratigraphic record, including both a floodplain and a channel component, has been
instrumental in developing this model, which can be tested in other parts of the Santa
Cruz River.
1. This age estimate is based on 18 of 19 radiocarbon dates from the site. A date
that did not fit within the average was 2240 ± 60 B.P.
Utilizing a method that details both the alluvial stratigraphy and site-reach
specific hydrologic factors influencing the Holocene floodplain record, this dissertation
offers a new interpretation of the middle to late Holocene archaeological record. Site
and reach specific data are critical to addressing questions beyond the level of
explanation that encompasses several hundred or even thousands of years. The
defining characteristics of Middle to Late Archaic transition in southern Arizona
include the transition to agriculture and changes in settlement and subsistence patterns.
Yet, the current application of geologic stratigraphy to this archaeological record of
change does little more than convey general trends in the human use of riverine
environments. New data on the Middle Archaic in the Tucson Basin, utilize a
high-resolution geologic record to demonstrate the importance of this level of alluvial
interpretation to understanding human use of the floodplain during this period.
By utilizing a site- and reach-specific sedimentological record in this thesis, the
research presented operates at a scale that is better able to address the changes
occurring in human land use during the transition to agriculture in southern Arizona.
The thesis employs stratigraphic records that cannot be correlated across the entire
Tucson portion of the Santa Cruz River, but that are specific to the area surrounding
the Santa Cruz Bend and Los Pozos sites. Historic and hydrologic records indicate
that the area from A-Mountain to the Rillito confluence would have responded
separately to small-scale changes (possibly as a result of intrinsic geomorphic factors).
Two topographic controls isolate the river, Rillito Creek and A-Mountain.
A-Mountain is in a part of the floodplain that is affected by local restrictions
on hydrologic processes. An impermeable stratum, created by the merging of
Pleistocene terraces with hard bedrock, limited downcutting and forced groundwater to
the surface, potentially creating a location favorable for sediment storage in the
A-Mountain area. This narrow portion of the valley also created an area that, during
more active flooding, would have transported sediments through the reach. Under a
meandering stream condition, like that of the middle to late Holocene, flood events
would occasionally erode the banks of the river.
Another important topographic influence on the focus reach is the presence of
Rillito Creek. Because the source of its drainage is the Santa Catalina Mountains, and
because the Santa Catalinas receive significant flood flows during periods with a high
incidence of tropical and frontal storms, subtle changes in the intensity of these storms
could promote sediment storage at the Rillito confluence. Contribution to the
hydrologic and sediment budgets in the area surrounding the Rillito confluence would
potentially have impacts on the upstream and downstream reaches of the Santa Cruz.
The internal record between A-Mountain and Rillito Creek, two locations that act as
thresholds of stream behavior, is representative, therefore, of the phenomena affecting
this reach during its Holocene history.
When the alluvial records from the study area are combined with records from
the area south of A-Mountain (near San Xavier Mission) and north of the Rillito (and
Canada del Oro) confluence (near Ina Road), it is obvious that there are geologic units
that can be correlated across this long stretch of the river and that there are geologic
units that cannot be correlated. Geologic records that can be correlated across the
entire Tucson portion of the river, including trends toward net aggradation, are
interpreted as the product of either significant climatic or hydrologic changes and,
predominantly, the effect of extrinsic processes. Geologic records that can be
correlated across shorter reaches are the product of either intrinsic geomorphic
processes or localized hydrologic changes (e.g., intensive localized storms or local
drops in the water table).
Long-Term Climatic Changes and the Geologic Record of the Santa Cruz River
Several geologic units appear to reflect long-term climatic or hydrologic
changes affecting the Santa Cruz River. An apparent, rather lengthy hiatus appears to
have preceded middle Holocene deposition of sediments on the Santa Cruz River.
Although none of the pre-middle Holocene sediments in the study reach have been
radiocarbon dated, the high degree of argillic accumulation in them suggests a late
Pleistocene or early Holocene age. Holocene sedimentation in the study reach
apparently begins between approximately 5,500 and 4,500 years ago. These sediments
are accompanied by evidence for a relatively high water table, suggesting that the
trend toward net aggradation that occurs during the middle Holocene is the result of an
increase in the hydrologic budget of the Santa Cruz River. This apparent wet trend
probably occurs in response to a long-term climatic change as reflected in
palynological and lacustrine sediments elsewhere in southern Arizona and across the
Southwest. Middle Holocene sedimentation occurs in the Santa Cruz River record and
is represented by Haynes and Huckell's (1986) unit B, dating between ca. 5000 and
2500 B.P.
The erosional contact represented between Haynes and Huckell's (1986) units B
and C (ca. 2500-2000 B.P.) is marked by an insignificant depositional hiatus in the
focus reach. A shift in depositional regime resulting from a decrease in channel size
and depth and causing increased floodplain sedimentation at the Los Pozos site (Figure
6.5, units Ilb and Ilia) occurs after this depositional hiatus. The small, shallow
channel created during deposition of unit ilia in the Los Pozos west side stratigraphic
pit would have supported large quantities of floodwater and sedimentation to the
floodplain, creating a favorable setting for agricultural economies.
Erosion of Haynes and Huckell's unit C appears to be quite significant,
affecting most of the Tucson portion of the river. In the study reach, this period is
represented by significant downcutting, creating a very deep and steep-sided arroyo.
The effect of this incision is felt upstream in the San Xavier Mission area and
probably reflects either climatic change or a breach of a significant geomorphic
threshold. Wells found at the Los Pozos and Wetlands sites appear to indicate a drop
in the availability of surface water during this period, perhaps reflecting the hydrologic
effects of a change in climate. Because records for the study reach are incomplete
following this period, there is no basis from which to correlate post-entrenchment
conditions with areas upstream and downstream of the study reach.
Short-Term Climatic Changes or Small-Scale Threshold Breaches
During the period between 4500 and 2800 to 2500 B.P., the study reach
displays a record of channel cutting and filling events not represented elsewhere in the
Santa Cruz River geologic record. Although these events could be present, but not
within the confines of the profiles examined by Haynes and Huckell (1986), Stafford
(1986) or Waters (1987, 1988), there is no evidence for similar changes occurring in
the area around A-Mountain, suggesting that A-Mountain acted as a threshold to
stream behavior. Stream behavior affected by this threshold would have created
different records upstream and downstream of A-Mountain.
Because these cutting and filling events are locally restricted, they represent
exceeded internal thresholds. Although such thresholds could be exceeded by
short-term changes in the frequency of tropical and frontal storms, they do not
constitute long-term climatic change. It is possible that sediment storage occurs at the
Rillito Creek confluence during short-term changes in the freqency of tropical and
frontal storms. Changes in the longitudinal profile of the stream caused by sequential
erosion and deposition would create localized microenvironments where sediment
storage was the dominant process, creating a succession of events representing what
Schumm (1973; Schumm and Parker 1973; Womack and Schumm 1977) has called
"complex response." Complex response refers to the lag time in the response of
individual reaches of a stream channel to a perturbation in the stream system. The
stream can be simultaneously incising in one reach while aggrading in another.
Previously, this concept has been viewed in stark contrast to the apparent synchroneity
of arroyo incision across the southern Southwest during both the historic (Bryan 1941;
Cooke and Reeves 1976) and prehistoric periods (Haynes 1968). However, utilizing
Parker's (1995) model, which focuses attention on the cause-and-effect relationships
between climatic/geomorphic perturbations and hydrologic response, synchronous
incision and asynchronous stratigraphic records can be the result of the scale of
perturbations to the stream system.
Slackwater and overbank deposits at the top of each aggradational column
would support the growth of native grasses and other foodstuffs near the river; these
plant taxa are represented in paleobotanical samples from the Los Pozos site.
Overbank deposition would also be conducive to small-scale agriculture. These
conditions are possible in reaches dominated by sediment storage.
As the position of stored sediment moves through the focus reach, favorable
microenvironments would not have been laterally extensive, and would have migrated
upstream and downstream over periods of 500 to 1,000 years (the time it takes for one
incised channel to aggrade completely). Over a space of 6 km this is roughly 15
m/year, and may influence the distribution of archaeological resources across the
landscape. The scale at which these local microenvironments would migrate up and
downstream would be imperceptible to human groups utilizing the area and is likely
not capable of being detected through radiocarbon dating. The small size of these
local habitat areas, detectable today only by intensive stratigraphic tracing of subtle
lenses of overbank deposition and probably not exceeding 25 ha in area, would be
enough to influence human population or seasonality of use of the area. During this
time populations moving into the area would need to rely on the surrounding bajada
areas to support subsistence needs, establishing a pattern of settlement that is
continued during episodes of more consistently reliable environmental conditions (the
period from 2800 or 2500 to 2000 B.P.).
Chapter 2 demonstrated that Middle Archaic use of the floodplain has been
underestimated and that, as a result, interpretation of Middle Archaic occupations in
southern Arizona has overemphasized use of the bajada and montane environmental
zones by Middle Archaic groups (Roth 1988, 1989; Huckell 1990). Preservation could
certainly be part of the difficulty, but recent research in the Santa Cruz floodplain has
illustrated the potential for Middle Archaic use of the area. Though occupation of the
floodplain is not as apparently intensive as during the Late Archaic period, it reflects a
pattern of seasonal land use that could be carried into periods of greater agricultural
Though human groups may not have been able to detect subtle changes in the
location of microenvironments from year-to-year, over several generations it would
have affected the location of their settlements. The discontinuous nature of these
microenvironments during the Middle Archaic would not have supported the large
settlements present during the more favorable Late Archaic period. During the Middle
Archaic period, the focus reach is dominated by complex response, meaning that
sediment storage, overbank deposition, and sediment entrainment migrate through the
stream system. Microenvironments would be present only in the study area and not in
other portions of the river dominated by sediment entrainment. Middle Archaic
populations cannot be expected to have used areas where discontinuous gullying was
the dominant sedimentary process.
Over the years, a number of models have been developed to account for early
agriculture in the American Southwest. In 1962, Haury proposed that maize entered
the Southwest by means of a "highland corridor." At the time, the earliest ages on
domesticated plant materials were maize from Bat Cave, New Mexico. Subsequent
refinement of the chronology of early maize (Berry 1982, 1985; Smiley and Parry
1990; Wills 1988b) provided the impetus for additional models of the spread of
Models of the Transition to Agriculture
Following on the highland theme offered by Haury (1962), Ford (1981) defined
what he called the "Upper Sonoran Agricultural Complex." His revision of Haury's
model would emphasize the use of these crops by hunter-gatherers living in these
highland regions. The agricultural crops both supplemented their diet of edible
resources and provided the disturbed environment favored by wild plant resources,
further enhancing these resources (Ford 1984).
Minnis (1985, 1992) favored a similar low-level integration of cultivated plants
into the subsistence-system of foragers. He further suggested that both opportunistic
and stress-based adoption of agriculture may have been involved.
Stress-based models have been adopted by a number of archaeologists (Hard
1986; Hunter-Anderson 1986; MacNeish 1992; Wills 1988a, 1988b, 1990) who argue
that either population growth and/or increasing environmental uncertainty caused
foragers to adopt agriculture to enhance resource predictability.
Other archaeologists have proposed that agriculture arrived in the Southwest by
means of immigrant populations from the south (Berry 1982; Berry and Berry 1986;
Huckell 1990, 1992a). Both models suggest that environment played a significant role
in the spread of agriculture from Mexico into the American Southwest. Basing his
model predominantly on the excavation of a number of San Pedro-aged sites, which he
views as distinctive in material culture from earlier groups, Huckell (1990, 1992a)
suggested that improved environmental conditions along rivers and streams in the
southern Southwest. Huckell further proposes that these immigrant populations
practiced a mixed fanning-foraging economy.
Results of the recent excavation of Los Pozos, and the addition of early
radiometric ages on maize throughout the Southwest, suggest that these models should
be reevaluated in light of new evidence.
New Chronology for Maize
One of the most evident results of refinement of the chronology for maize has
been that the dramatic difference in time between highland adoption of agriculture and
the adoption of maize by desert groups was no longer remarkable (Smiley and Parry
1990). Since the first application of AMS technology to early maize dates, more
evidence for early agriculture has appeared in questionable or possibly contaminated
contexts. New evidence from the Los Pozos site, along with these early dates on
maize, may record the introduction of agriculture in the American Southwest.
Over the past seven years new dates on maize have exceeded the earliest dates
from caves, rockshelters, and alluvial sites by several hundred years (Table 7.1). The
date on maize from the Los Pozos site threatens to break that boundary by several
hundred years more, but, when viewed as a group, the dates are less remarkable.
Figure 7.1 illustrates the calibrated radiocarbon age ranges on early maize dates in the
American Southwest. It must be noted that most of these individual samples have
been questioned for one reason or another. The early date from Stone Pipe was
located in an unusually stained sediment that was interpreted as possible chemical
contamination, lending suspicion to the date. Similar questions of contamination
orcontext have been advanced for early maize dates in other parts of the Southwest.
Table 7.1.
Earliest radiocarbon dates of cultigens in the Southwest (2500 B.P. for maize; 1700
B.P. for other cultigens, after Mabry 1996a).
Date (B.P.)
Lab No.
3370 ± 60
D. Seymour, P.C.
3610 ± 170
2880 ± 140
Smiley and Parry
3445 ± 45
3135 ± 45
3050 ± 50
Gilpin 1994
Gilpin 1994
Gilpin 1994
Sheep Camp
2900 ± 230
Simmons 1986
LA 18091
2720 ± 265
Simmons 1986
Salina Springs
2630 ± 45
Gilpin 1994
3740 ± 70
3120 ± 70
3060 ± 110
3010 ± 150
2980 ± 120
2780 ± 90
2690 ± 90
2630 ± 90
2140± 110
Wills 1988
Wills 1988
Wills 1988
Wills 1988
Wills 1988
Wills 1988
Wills 1988
Wills 1988
Wills 1988
2470 ± 250
1900 ± 70
Wills 1988
Wills 1988
Upham et al. 1987
Tagg 1996
Tagg 1996
Upper Rio Grande Valley
LA 10577
Colorado Plateau
Three Fir Shelter
Mountain Transition Zone
Bat Cave
Tularosa Cave
Southern Basin and Range Province
3175 ± 240
Fresnal Shelter
2945 ± 55
2880 ± 60
Date (B.P.)
Lab No.
2540 ± 200
2085 ± 60
2015 ± 65
1955 ± 55
Carmichael 1982
Tagg 1986
Tagg 1986
Tagg 1986
2930 ± 45
2915 ± 45
2910 ± 45
2780 ± 90
2775 ± 60
B. Huckell et al.
B. Huckell et al.
B. Huckell et al.
B. Huckell 1988
B. Huckell et al.
Solar Well
2835 ± 85
2815 ± 80
2800 ± 140
2590 ± 75
B. Huckell 1990
B. Huckell 1990
B. Huckell 1990
Cortaro Fan
2790 ± 60
2595 ± 70
B. Roth, p.c.
B. Roth, p.c.
West End
2735 ± 75
2675 ± 80
B. Huckell 1990
B. Huckell 1990
2580 ± 60
2520 ± 40
2500 ± 60
M. Diehl, 1996a
M. Diehl, 1996a
M. Diehl, 1996a
2565 ± 75
B. Huckell 1990
Matty Canyon
2505 ± 55
B. Huckell 1995
Eagle Ridge
1725 ± 65
Elson et al. 1995
• Denotes floodplain site
0 I MN
G C11:11
LA -0276,3
Direct dates on
maize from Tucson
Basin sites
(>2500 B.P. RCY).
AA -12054
- 01074
AA -12055
Earliest direct
dates on maize
from the American
Fresnal Shelter
OO Luchachuki
IMMI:1 LA 10577
9- 86544
l• II0 Luchachuki
Anomalous direct
date on maize -H ON
I 1 • Square Hearth
from the Tucson Basin.
Los Pozos Middle
Archaic-Dates on wood charcoal.
10 1
..._ Los Pozos Middle Archaic date on maize.
CAMS - 34923
Figure 7.1.
Calibrated radiocarbon age ranges on early maize in the American
Southwest (after Gregory 1996a).
In 1992, maize cupules were recovered from an alluvial lens at the Los Pozos
site (Huckell personal communication 1997). An unpublished radiocarbon date on the
maize is a few hundred years older than a wood charcoal date from the same deposit.
Because the maize age and charcoal from the alluvium were out of sequence and
roughly 300 years apart, he assumed that the maize date must be in error (Huckell,
personal communication 1997). The addition of the 4050 ± 50 B.P. date from the Los
Pozos site in a stratum dating roughly the same age, raises the question of whether
these early dates could represent the migration of agriculturally capable groups into the
area, establishing a presence after the Altithermal warm period. Both dates are in a
more secure context and lack the potential indicators of contamination that are present
in other early Southwestern samples.
During the succeeding Late Archaic period, groups living in southern Arizona
moved toward an agriculturally dependent, at least semi-sedentary society. By 2500
B.P., maize agriculture along the Santa Cruz River was fairly well-developed. The
earliest of these large sites (early Cienega phase, ca. 2600-2400 B.P.) typically
displays a number of extramural pit features and a few pit structures, as demonstrated
by archaeological excavations at the Wetlands and Clearwater sites. By 2400 B.P.,
large villages with hundreds of pit structures are present along the floodplain of the
Santa Cruz. Initial research suggests that these large villages are only present within
the study area; however, intensive research such as has been conducted over the past
four years has not been conducted in other parts of the Santa Cruz River Valley.
Additional planned cultural resource management of portions of the interstate corridor
north of Ruthrauff Road and south of A-Mountain will determine whether the pattern
of occupation present at sites in the study area is repeated elsewhere in the valley.
The Relationship between Stream Changes and the Adoption of Agriculture
The record of stream changes recorded at the Los Pozos site and elsewhere in
the study and focus reaches provides a mechanism for the adoption of agriculture by
groups in southern Arizona. Huckell (1990, 1992a) has suggested that immigrant
groups, arriving from Mexico following the Altithermal hiatus, responded to valley
aggradation in southern Arizona by moving into the area. In his model, valley
aggradation begins roughly 4,500 years ago, but human groups capable of agriculture
do not enter the area for about 1,000 years. Their sudden appearance displaces or
overtakes the Middle Archaic population already living in the area.
The record of stream changes suggests, however, that small microenvironments,
similar to those found during the Early Agricultural period, are present in parts of the
river immediately following middle Holocene aggradation. The possibility that these
microenvironments are occupied by Middle Archaic groups with the capacity to
cultivate maize suggests that either the microenvironments and their preservation were
too small to leave a record as robust as that found during the Early Agricultural period
or that the areas were too small to allow large groups of people to exploit this part of
the landscape.
During the Early Agricultural period, stream changes provide the impetus for
these same groups to enhance their use of the floodplain. Increased sedimentation
over larger geographical areas provided a large, favorable riverine environment,
capable of supporting large-scale agriculture. For approximately 500 years, this Early
Agricultural population thrived in a floodplain environment that contributed large
quantities of fresh sediment and water to the floodplain, creating an environment
conducive to agricultural production.
Prehistoric processes acting on the Santa Cruz River have preserved Middle
Archaic sites in some localities. Individual areas or reaches may experience different
processes either enhancing sediment entrainment or sediment storage. Along the river,
there exist features which have acted historically as controlling mechanisms,
preventing thresholds from being exceeded in reaches upstream or downstream of
those features. Only during significant events are critical thresholds surrounding these
features also exceeded. Preservation between each of these features should be
predictable, but may not be the same as preservation in reaches downstream or
upstream of that feature.
In the San Xavier Mission area, middle Holocene sediments appear to be
preserved only along the valley margins as slopewash deposits. Although the middle
Holocene sediments at the Los Pozos site are also located along the valley margin,
they appear to be floodplain rather than slopewash sediments, indicating the potential
for additional preservation of middle Holocene sediments in this reach. At the
Clearwater archaeological site, near A-Mountain, sediment storage is a dominant
process throughout the middle Holocene and may have the potential to preserve
Middle Archaic archaeological sites. A 3,000-year old feature uncovered in
archaeological trenches that exceeded the OSHA-regulated depth may be the clue of
this earlier preservation.
It is also possible that additional Middle Archaic sites will be discovered in the
area between Ruthraff and Ina Roads where sediment input from the Rillito and
Catlada del Oro washes may be high, enabling much of the area to preserve, rather
than erode middle Holocene sediments. Both the preservation of Middle Archaic aged
charcoal at the Ina Road railroad locality (Haynes and Huckell 1986) and the general
uninterrupted aggradational sequence in the Ina Road area documented by additional
studies in the Ina Road area, suggest that preservation may be the dominant process in
this area.
The interpretation of human response to environmental changes is highly
dependent on the scales of the two records being observed. This interpretation works
best when short-term catastrophic events such as volcanism, earthquakes, or flooding
both preserve the archaeological record in the geologic matrix and demonstrate a direct
human response to sudden changes. The second most common level of
archaeo-environmental interpretation involves long-term changes in climate (i.e., the
Pleistocene to Holocene transition, the Altithermal drought, etc.), that are often tied to
long-term changes in human "adaptive" patterns (i.e., large scale migrations, dramatic
changes in human subsistence, such as hunting-gathering to agriculture). This broader
level of analysis, although useful as a framework for archaeological research, is at too
gross a scale to address questions about subtle shifts in human use of the landscape
and even more subtle changes in mobility and subsistence.
Most archaeologists today recognize that our knowledge of Archaic
hunter-gatherer groups has moved beyond the level of reconstructing "adaptations" to
reconstructing prehistoric phenomena at the scale of differences between residential
and logistical mobility or differences between two scales of logistical mobility.
Environmental data, derived from an alluvial stratigraphic record that measures only
large-scale changes in hydrology, can offer little assistance in understanding these
more fine-grained aspects of the archaeological record. An approach that considers the
implications of small-scale geologic changes as they are reflected in that stratigraphie
record can provide resolution of the human-environmental interface at a scale that is
appropriate to the research questions of the future.
The following descriptions of geologic map units are from McKittrick (1988):
The most active portion of the main drainage channels. Washes commonly
contain coarse to fine-grained sand exhibiting bar-and-swale topography. The
channel position is unstable and subject to rapid migration within the finergrained floodplain deposits that include terraces 1 and 2. It is the
topographically lowest unit in the map area, and is frequently too young to
support dense vegetation. These areas are flooded frequently.
Active and recently active channel deposits that are associated with incised
channels, except in Avra Valley, where main axial drainage is wide,
aggradational, and unconfined. The unit includes a complex of low terraces,
active channels, gravel bars, and floodplains. The average height of the lower
terraces above the active channels is about 1 m. These areas are subject to
occasional frequent flooding and sediment transport.
Youngest and lowest terrace that has been recently abandoned. Soil
development is very weak to non-existent.
Flat, well-preserved terraces associated with modern floodplains of the Santa
Cruz River, Rillito Creek, and Pantano Wash. Lies topographically above ti
but below t2. Surfaces are generally well preserved and lacking in erosional
modification. Soil development consists of weakly indurated Entisols.
Generally narrow, poorly defined terraces that are intermediate in height
between t2 and t4. Soils appear to contain moderately developed color and
structural argillic horizons with little carbonate accumulation. Corresponds to
the Jaynes terrace of Smith (1938).
Broad terrace covering a large aerial extent in the central Tucson Basin area.
Soils typically contain a fairly well-developed argillic horizon with varying
degrees of secondary carbonate accumulation. Corresponds to the Cemetery
terrace of Smith (1938).
Highest, oldest terraces in the map area. These terraces form elongate ridges
that may represent the surface of a former level of maximum alluvial fill in the
Tucson Basin; they correspond to the University terrace of Smith (1938).
Active or recently active alluvial deposits. These deposits commonly form thin
veneers that mantle older map units. Fan surfaces often contain a concentration
of coarser pebbles at the surface that mantle underlying silt, although this
surface armor is loose and not continuous. Surface clasts show no rock
varnish. The unit is typically lower in relief than older fan surfaces. It covers
a portion of Avra Valley but is primarily confined to small fans close to the
mountain fronts in the rest of the map area. Gullies that originate on fan
surfaces are usually less than 0.5 m deep and may be either erosional or
distributary. Soils are very weakly developed, if present at all, reflecting the
young age and recent activity of the unit. This unit should be considered to be
potentially subject to flooding and sediment transport.
The youngest alluvium abandoned by active depositional processes. This unit
is older than Y and generally younger than Ml, but it ranges between these
two units in age and surficial characteristics. A slight pavement occurs on
many of the fan surfaces, with surface clasts typically averaging 2 cm in
diameter. Varnish is rare, although surface clasts can have a slight pinkish hue
in some locations. The surface of this unit is generally intermediate in height
between M1 and Y. Interfluves are usually flat to slightly rounded. Gullies
originating on fan surfaces range from less than 0.5 m to 4 m in depth.
Surface expression varies from being fairly flat and smooth to gently
undulating. Soil development varies from slight development (Entisol) with a
brownish surface color to moderately well-developed argillic horizons (Typic
Haplargid) and even petrocalcic horizons in a few areas, although the presence
of a petrocalcic horizon usually indicates the occurrence of a buried older
deposit. Variations in depth and density of dissection cause portions of this
unit to be susceptible to flooding during larger events.
Relatively old geomorphic unit of wide aerial extent. Surfaces tend to have a
slight pavement development where concentrations of fairly well-sorted clasts
averaging 2 to 3 cm in diameter partially armor fan surfaces. A reddish rock
varnish is common on surface clasts. The fan surface is typically hummocky
and has well-rounded interfluves.
Channels heading on fan surfaces are broad and V-shaped, contain sandy
floors, and range up to 5 m in depth. Soils commonly contain a petrocalcic
horizon with or without an overlying red, clay-rich argillic horizon (Paleargid
or Paleorthid). These surfaces are isolated from active fluvial processes, and
only gullied areas are subject to flooding.
Highest and oldest alluvium in the map area that retains a preserved
geomorphic surface. This unit encompasses all surfaces that are higher in relief
than M1 and may range widely in age. Fans are frequently cored by bedrock
on all of the mountain fronts. Surfaces have slight pavement development
consisting of scattered clasts overlying silt. A reddish rock varnish is common
on the surface clasts in some location, although absent in other. Interfluves are
very rounded, broad, and V-shaped. Gullies heading on fan surfaces range
from 1 m to 15 m in depth. Soil development consists of thick petrocalcic
horizons at or near the fan surface (Paleorthid) unless removed by erosion.
Argillic horizons are not common, although they do occur locally in
particularly stable areas. Flooding is restricted to gullies.
Qtbf Alluvium that does not exhibit a preserved geomorphic surface. This unit is
usually higher in relief and probably older than Ml, although wherever fan
surfaces are absent, the surface age cannot be determined. Flooding is
restricted to gullies.
The following sedimentary descriptions are compiled from unpublished
fieldnotes taken by Huckleberry in 1995 and Freeman in 1996.
502. Dark grayish brown (10YR 4/2) silty clay; weak, medium, angular blocky
structure; many, fine carbonate filaments; diffuse, smooth boundary; overbank
alluvium modified by pedogenesis.
503. Pale brown (10YR 6/3) silt; massive; two thin, discontinuous, silty clay layers;
moderately bioturbated, very few, very fine oxide stains; abrupt wavy boundary;
overbank alluvium.
504. Dark grayish brown (10YR 4/2; 10YR 3/2 to 3/3 when moist) silty clay; weak,
medium, angular blocky structure; contains silt laminae and charcoal; slightly
bioturbated; abrupt wavy boundary; overbank alluvium.
505. Pale brown (10YR 6/3) silt; massive; few fine carbonate filaments; abrupt wavy
boundary; overbank alluvium.
506. Grayish brown (10YR 4/2; 2.5Y to 10 YR 3/2 when moist) silty clay and pale
brown (10YR 6/3) silt; weak, medium, angular blocky structure; common, fine,
carbonate filaments; slightly bioturbated; abrupt wavy boundary; overbank alluvium,;
contains cultural features and frequent charcoal flecks and small chunks.
507. Pale brown (10YR 6/3) very fine sand with low angle, trough cross beds;
massive; few, fine, soft carbonate masses; abrupt wavy boundary, smooth in places.;
overbank alluvium.
508. Grayish brown (10YR 5/2) silty clay and pale brown (10YR 6/3) silt; weak,
medium, angular blocky structure; common, fine, carbonate filaments; slightly
bioturbated; abrupt wavy boundary; overbank alluvium.
509. Pale brown (10YR 6/3) silt to very fine sand; massive; few carbonate masses;
abrupt smooth boundary; overbank alluvium.
510. Brown (7.5YR 5/2) silty clay; weak, medium, angular blocky structure; common,
fine, carbonate filaments and medium nodules; contains artifacts and charcoal; diffuse,
smooth boundary.; overbank alluvium modified by pedogenesis.
510a. Dark grayish brown (10YR 3.5/2) clay loam; moderate carbonate coatings on
fine subangular blocky ped faces; probably a Btk horizon; forms a clear boundary with
the underlying 510b; ca 4-5 cm thick.
510. Grayish brown to light grayish brown (10YR 5.5/2 to 10YR 6/2) clay loam with
many grayish brown (10YR 5/2) mottles and very few, very fine Mn/Fe and oxide
stains; few carbonate stringers; peds are fine to medium subangular blocky; forms a
clear boundary with the underlying 510c; ca 14 cm thick.
510c. Light brownish gray (10YR 6/2) and grayish brown (10YR 5/2) silty clay loam
with many medium to fine dark grayish brown (10YR 4/2) mottles; very few, very
fine carbonate stringers and very few flecks of charcoal; structure is massive to very
fine subangular blocky; forms a clear boundary with the underlying 510d; ca 17 cm
510d. Very dark to dark grayish brown (10YR 3/2 to 4/2) clay loam with light
brownish gray (10YR 6/2) mottles; many very fine Mn/Fe and oxides (orangish to
reddish brown); some intrusion of Unit 510c through bioturbation; forms abrupt
boundary with underlying Unit 511.
511. Light gray (10YR 4/2) to very pale brown (10YR 7/2.5) silt; compact, massive,
and relatively unmodified, but with some platy sedimentary structure still present);
contains some "rootlets" which may actually be the remains of organic material
covered as this unit was deposited over the top of Unit 512; upper boundary with Unit
510 abrupt, lower boundary with Unit 512 very abrupt; marks the onset of
sedimentation after a hiatus marked by soil formation at the top of underlying Unit
512; appears to be part of the same series of deposition as the overlying Unit 510, but
the absence of pedogenic qualities seen in Unit 510 makes this a distinct depositional
512. Dark grayish brown (10YR 4/2) to grayish brown/light grayish brown (10YR
5.5/) clay loam; the colors are mottled in roughly equal amounts, although the soil
takes on the general appearance of the darker color in the cross section; some silt is
present throughout the unit, and is probably the source of the lighter color; some
banding is dimly visible but diffuse, and this sediment was probably originally a series
of bands, but pedogenic processes, bioturbation, and compression have made it
difficult to distinguish distinct sedimentary episodes; a thin silt band is slightly more
predominant in the lower (ca. 5 cm) in places (Unit
513. forming a sedimentary horizon marked by an abrupt to clear boundary with the
upper portions of the unit; some very fine Mn/Fe and oxide stains and abundant
rootlets throughout; structure of the upper half is platy in appearance, while the lower
half is fine subangular blocky; abrupt boundary with the overlying Unit 511 is marked
by soil formation (Btk) at the top of Unit 512.
514a 1. Dark grayish brown (10YR 4/2) clay loam with light brownish gray (10YR 6/2)
mottles of silt to silty clay loam; moderate, fine carbonate filaments; structure medium
to fine subangular blocky; forms an abrupt, smooth boundary with Unit 512 (513)
above and a clear to gradual boundary with 514a 2 below.
514a 2 . Grayish brown (10YR 4.5/2 to 5/2) clay loam to silty clay loam, finely mottled
with the two colors; moderate, fine carbonate filaments and few very fine Mn/Fe and
oxides; gradual boundary with Unit 514b below.
514b. Light brownish gray (10YR 6/2 and 10YR 4/3.5) silt loam; compact and
massive to blocky structure; bioturbation bringing in materials from upper and lower
units; gradual boundary with Unit 514c below.
514e. Very dark grayish brown (10YR 3/2 to 3/3) clay loam with few, fine Mn/Fe and
oxides; moderate to many carbonate filaments; structure medium subangular blocky;
gradual boundary with underlying Unit 515
515. Very dark grayish brown (10YR 3/2 to 3/3) when moist and dark grayish brown
(10YR 4/3 to 4/2) when dry, sandy clay loam with some fine pebble gravel (ca. <2
cm), possibly representing reworked materials from the north or from Unit 516 below;
massive, very compact when dry; lower boundary is clear to abrupt and forms an
erosional surface.
516. Very gravelly loam, approx. 10 YR 6/2, pebble gravel (pea-sized) with some
oxide staining.
517. Reddish, grayish brown coarse sand and very fine pea gravel with small cobbles
(6-10 cm in diameter); abrupt boundary with Unit 516 above.
520. Channel deposits. Medium to coarse sands and occasional clay laminae.
531. Brown (10YR 4/3) sandy silt; gradual boundary with Unit 532 below.
532a. Yellowish brown (10YR 5/4) silt
532b. Brown (10YR 4/3) silty clay; some fine iron oxides stains.
532e. Dark yellowish brown (10YR 4/4) silt.
533. Brown to dark grayish brown (10YR 4/2 to 4/3) silty clay.
534. Dark yellowish brown (10YR 3/4) silt.
535. Reddish brown clay.
536. Yellowish brown silt.
540. Reddish brown muddy gravel.
The following sediment descriptions are taken from unpublished fieldnotes
taken by Andrea Freeman and David Gregory in 1996. Depositional units are labelled
in arabic numerals (e.g., 1-69), while stratigraphic units are labelled with roman
numerals (e.g., I, lia, etc.).
1. Modern disturbance. Pale brown sandy clay.
2. Pale brown silty clay; moderately compact, blocky; overbank alluvium.
3. Pale brown silt; compact; numerous carbonate filaments; overbank alluvium.
4. Brown silty clay; overbank or slackwater alluvium.
5. Pale brown silt; overbank alluvium.
6. Dark brown clay; overbank or slackwater alluvium.
7. Pale brown silt; overbank alluvium.
8. Two clay dark brown bands separated by a small thin band of silt; boundaries are
wavy and indistinct; overbank alluvium.
9. Pale brown sandy silt; massive; overbank alluvium.
10. Dark brown clay band; overbank of slackwateralluvium.
11. Pale brown silt; overbank alluvium.
12. Dark brown clay; overbank or slackwater alluvium.
1. Modern disturbance
2. Pale brown silty sand; moderately compact; overbank alluvium.
3. Pale brown silt; compact; numerous carbonate filaments; overbank alluvium.
4. Brown silty clay; overbank or slackwater alluvium; weak pedogenic alteration in the
upper portion of this unit; underlying the thin upper band of clay is a medium brown
silt, followed (underneath) by a clay drape. This clay drape becomes thicker at both
ends of the trench and pinches out near the center of the trench to a very thin (ca. 1-3
cm) band.
5. Pale brown silt; overbank alluvium.
6. Grayish brown silty clay; overbank or slackwater alluvium.
7. Pale brown silt band; overbank alluvium.
8. Dark brown clay; overbank or slackwater alluvium.
9. Medium brown (when damp) sandy silt; massive; overbank alluvium.
10. Two clay dark brown bands separated by a small thin band; boundaries wavy and
indistinct; charcoal flecks at contact with 11, highly oxidized at lower boundary;
overbank alluvium.
11. Pale brown sandy silt; massive; overbank alluvium.
12. Medium brown silt (ca. 40 cm thick) and dark grayish brown silty clay; overbank
or slackwater alluvium.
1. Modern disturbance.
2. Pale grayish brown sandy silt, compact; overbank alluvium.
3. Pale brown silt and sand; many fine carbonates in bottom third; overbank alluvium.
4. Dark grayish brown silty clay; overbank alluvium.
5. Pale brown silt; overbank alluvium.
6. Dark brown silty clay; overbank alluvium.
7. Pale brown silt; overbank alluvium.
8. Dark brown silty clay; overbank alluvium.
9. Pale brown silt; overbank alluvium.
10. Dark brown silty clay; overbank alluvium.
TRENCH 94 (east segment)
1. Modern disturbance
2. Grayish brown silt; compact; some carbonate filaments; overbank alluvium; contains
several cultural features (possibly Hohokam).
3. Grayish brown to brown silt; more compact than 2 and more carbonate filaments;
overbank alluvium.
4. Dark grayish-brown silty clay; overbank alluvium.
5. Pale brown silt; overbank alluvium.
6. Dark brown silty clay; overbank alluvium.
7. Pale brown silt; overbank alluvium.
8. Dark brown silty clay; overbank alluvium.
9. Pale brown silt; overbank alluvium.
10. Two dark brown silty clay bands separated by a thin, pale brown silt band;
overbank alluvium.
11. Pale brown sandy silt and sand; overbank alluvium.
Unit Ia
1. Massive gravel (ca. 2-6cm.) and very coarse sand (la); larger cobbles (ca. 6-15 cm)
form a facies at the very eastern corner of the profile (lb); poorly sorted,
clast-supported; forms an abrupt, conformable and flat boundary with 2.
2. Gravel (ca. <2 cm., few 2-6 cm.) and very coarse sand; some sedimentary structure
present (laminated bedding); forms a very abrupt, conformable and flat to slightly
undulating (at west end of trench) boundary with 3.
3. Medium to coarse sand; lamellar-horizontal bedding (beds slope downward to the
east); some oxidation in spots (ca. 5 cm. diam.); abrupt boundary with 4, a facies
which cuts 3 to the west; at the eastern edge of the exposure, 4 has deposited a gravel
lag atop 3 and below deposit 5, forming a very abrupt boundary.
4. Coarse to very coarse poorly sorted sand and pea gravel; includes several lenses of
sand and gravel separated by medium to coarse, well-sorted sand lenses; occasional
large cobbles in upper coarse sand and gravel lens; forms an abrupt, conformable, flat
boundary deposit 5 (above); some magnetite placer deposits present.
5a. Coarse sand (5a); lamellar-horizontal sedimentary structure; abundant large
oxidation stains, especially in upper part of deposit.
5h. Pale brown (I0YR 6/3) medium to fine sand and silt; massive, no sedimentary
structure; upper portion is primarily fine sand and silt with carbonates, the latter
consisting of long strings of carbonates; some magnetite placer deposits present.
Unit lb
6a. Pale gray (10YR 7/2) coarse sand (6a); some weak horizontal bedding still present;
thin carbonate formed at top of the unit; forms an abrupt, flat and conformable
boundary with underlying deposits; coarse substrate of 6a correlates with dipping to
north visible in the east and north walls of the excavation; 6a fines upward into 6b.
6b. Pale gray (10YR 7/2) to very pale brown (7/3) fine to medium sand; forms a clear,
unconformable boundary with overlying deposit 7.
7. Pale brown to very pale brown (10 YR 6.5/3) silt and carbonates, with many large
carbonate stringers; massive sedimentary structure; clear, conformable boundary with
overlying 8.
8. Pale brownish gray to pale brown (10YR 6/2.5) medium sand and carbonates;
massive sedimentary structure; coarser sand and bedding to the north (opposite trench
wall) with abundant iron and manganese oxide/hydroxide staining; forms a very
abrupt, conformable boundary with 9.
Unit Ic
9a. Dark brown (10 YR 6/1 to 6/2) clay with many very fine, dark grayish brown
(4/2) to brown (7.5 YR 5/2) manganese and iron oxide/hydroxide stains; fine
subangular blocky structure; approximately 5 cm thick; strongly effervescent.
9b. Dark brown (10 YR 6/2) silt to silty clay; fine to very fine subangular blocky
structure; approximately 10 cm thick. Possible grass fire at lower boundary noted in
east wall consisting of charcoal and oxidized sediment.
9c. Grayish brown (10 YR 5/2) clay loam with many very fine, very dark gray (10 YR
3/1) stains and pale brownish gray (10 YR 6/2) silts; medium subangular blocky;
approximately 15 cm thick.
9d. Pale brownish gray (10 YR 6/2) massive silt; approximately 5-6 cm thick.
9e. Dark gray to gray (10 YR 4.5/1) clay loam with charcoal; very fine subangular
blocky structure.
Unit Ha
10. Medium sand (10a) with a facies of coarse sand and small gravels (10b) to the
west at the bottom.
11. Silt band; moderately compact.
12. Bands of clay, silt, and sand with some small gravels.
13. Fine sand.
14. Dark brown clay band; thin (ca 1 cm).
15. Silt to clayey silt with some weak banding.
16. Pale brownish gray (10 YR 6/2) medium sand, but with some organic matter;
massive with occasional silt/clay nodules; some very weak sedimentary structure
visible; very abrupt, unconformable boundary with underlying 9; very abrupt boundary
with overlying 11; no effervescence.
Unit IIb
17. Pale brownish gray (10 YR 6/2) silt band; slackwater deposit, very thin (ca. 1-2
cm); conformable boundary over 10 and over other Channel I deposits; moderately
18. Fine to medium sand with some cross-bedding structures still visible; expansion of
channel or channel margin/ wavy band of silt/clay and carbonates; shows up in center
of deposit and appears to separate two separate deposits of cross-bedding; a silt
deposit caps deposit 12, which begins formation of a series and silt and clay bands;
this finely laminated sand also has magnetite laminae present, some micro crossbedding, subsequently disturbed by bioturbation and carbonate formation; no
effervescence except where carbonates in upper deposit have translocated downward.
Unit III
19. Massive silt with strong carbonates; forms an abrupt but wavy boundary with 14;
this silt may actually be deposit 12; strongly effervescent.
20. Sand.
21. Dark clay band; thin (ca 1 cm).
22. Sand.
23. Clay loam to silty clay loam and silt loam occurring in a series of wavy bands;
lowermost clay contains some charcoal and many fine oxides; upwelling of this
deposit through the silt below (deposit 13) is visible in places (deposit is ca. 15-20 cm.
thick); fine to medium subangular blocky; an abrupt, conformable boundary separates
this deposit from 15 (above) in the east end of the trench; to the west this boundary is
clear; some effervescent bands; medium subangular blocky to columnar structure;
charcoal present in lowest darkest clay band (10YR 5/2).
24. Clay loam (10YR 5/2) to silty clay loam (10 YR 6/2) (dark in upper 3-4 cm);
medium subangular blocky structure (20-30 cm thick); forms a very abrupt,
conformable, and flat boundary with 16 (above); strongly effervescent in center of
deposit and toward bottom; no effervescence in upper 5-10 cm; fine columnar
structure, very abrupt upper boundary.
25. A series of clay (10 YR 5/2) and silt (10 YR 7/2) bands; wavy but conformable;
forms a wavy, conformable, abrupt boundary with the silt above (17), but is part of the
same depositional deposit; massive to medium subangular blocky structure; moderate
to weak effervescence throughout.
26. Silt (10YR 7/2), thicker to east of profile (more yellow, no carbonates compared to
deposit 13); massive; forms an abrupt, wavy, conformable boundary with 18 (above);
moderately effervescent.
27. Clay band (10 YR 5/1 to 5/2)(dark), pinches out to east where the silt (below) is
thicker; medium subangular blocky structure; forms a clear, wavy but conformable
boundary with 19 (above); no effervescence.
28. Paler colored sandy clay loam with abundant carbonates. Fine to medium
subangular blocky structure. Forms a very abrupt unconformable boundary with
deposit 20 (above). Medium brown (10 YR 6/2) silty clay; thin band of sand follows,
forming a very abrupt upper contact with that sand; moderate effervescence; fine
subangular blocky to columnar structure
Unit IVa l
29. Coarse sand
Unit IVa2
30. Silt and fine sand with numerous carbonate filaments.
Unit IVa3
31. Silt and fine sand with numerous carbonate filaments.
Unit IVb
32. Small to medium sized cobble gravels and coarse sand
Unit IVc
33. Floodplain facies; silt and clay bands.
34/21. Medium sand with some carbonates and organic matter in upper portion of the
35. Compact silt; some carbonate filaments toward top.
36. Fine sand and silt; bedded.
37. Compact silt.
38. Very dark brown sandy clay; many carbonate filaments and abundant evidence for
organic matter.
39. Very fine sand and silt
40. Dark brown silt; abundant organic matter.
Unit V
41. Compact silt.
42. Fine sand; magenite placer deposits present in laminae.
43. Coarse sand and pea gravel.
44. Clay
45. Silt
46. Medium sand
47. Coarse sand/small gravels
48. Silt
49. Coarse sand
50. Silt
51. Sand
52. Sand
53. Coarse sand with some small gravels.
54. Two dark clay bands separated by a silt band
Unit VI
55. Medium and coarse sand; laminar bedding.
56. Clayey silt band.
57. Fine sand, well sorted; prominent iron or manganese oxide mottling toward the
west near flood channel (57a); common charchoal flecks; becomes progressively finer
to the east, grading into finely bedded sandy silt and silt (57b).
58. Clayey silt band.
59. Dark clay bands; thin (ca 1 cm).
60. Medium sand.
61. Silty clay, progressively siltier toward the east; prominent iron or manganese oxide
mottling near flood channel (62)
62. Medium to coarse sands (62a), moderately well-sorted; grades into medium,
moderately well-sorted sand to the west (62b); a high energy flood deposit.
63. Clay band with charcoal flecks at top.
64. Silty clay; this unit may represent modern disturbance or possibly a cultural
65. Dark clay band; thin (ca 1-2 cm.)
Other Deposits
66. Coarse sand with some medium to coarse gravels at the top in places (lag gravels
?); poorly sorted; faint iron or manganese oxide mottling except adjacent (ca. 1 m) to
flood channel (62), where mottling is prominent.
67. Three clayey silt bands (ca 5-7 cm) separated by sands; strong to medium,
prismatic to blocky structure; prominent iron or manganese oxide mottling near flood
channel (62; ca. 1.5 m).
68. Fine sand; well-sorted; more compact near the top with few carbonate filaments.
69. Modern disturbance
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