lIluiutr.atty of Ari;::oua College of Agriculture CALICHE IN ARIZONA

lIluiutr.atty of Ari;::oua College  of Agriculture CALICHE  IN  ARIZONA
April 15, 1930
Bulletin No. 131
lIluiutr.atty of Ari;::oua
College of Agriculture
Agricultural Experiment Station
CALICHE IN ARIZONA
]. F.
BRF..o\ZEALE AND
H. V.
SMITH
PUBLISHED RY
1lninfl1lttu of Armma
TUCSON. ARIZONA
ORG.-,\r.;IZo\T!ON
11"'''11) <If 1I~:(JRNTlI
nlS FH'l:CF.LI.~::':CY. Jlln~ C. I'IIII.I.II'S, G~ver"'lr (Es-olllciol_ .... _ ••• __ ._. __ .... _ •.. I'hoeak
IIU!!. OllJr.RLY.S O. CASR. Slat. Sul'.rialend....t (Ez.oIIIdo) .................... _ _ .. _ ......... _.I>boeub
80S.
liON.
HON.
HON.
HO)l.
liON.
(roN.
HON.
Al'l'ol,,"·" Membt'"
ROBRRT R. TALI.Y. U.S.• .t.I.I':•• Cbne>tII<l._ .... _ .... _ ................ _._ .. ___ •.. __ .Jetam.
OHARI.F.>; M. I.A YTON._ ............................. _ ........··.......· ......····_······...... _ ............. _.Sallord
GEORnv, II. RIiIDGI!:, Tre.911l"" .......................... _. __ .....·· •••• _._ ........ _ ... _ ... __ .. 8otnerto..
ROV KIRKPATRICK. 1I.~ .... tary ...................................................... ···• __ .. _ .. _ .......... _.GlolN
FRANKI.I~ J. eUII'I:II. M.S., \'1""·Ch~ncello .... _._ .. _.................. _ ............. _ ...... Su"erior
TH~:Oll(lllA l.I.\lI~II ........................................._.• _.................. _.............. _ .. __ .. __ .Nol!lliel
WII.LIAl.I C. JUn,':R.......... _........................_... _ .... __ ·_..·............·.. _ ••••• _....... _Phoen;~
HENR\' L. lIcCLUSKEY ....... _................... _ ............... _ ............ _ ............ ___ ..... _ ...... Phoenl~
HOliER L. SIIA!>1TZ. Ph.D., ik.D ......... _ .................................. _ .... _ ... l~dellt 01 the U"I ...."lt,.
El:l'ERll1F.)1T STATION STAFF
ELKER D. BALL. )I.S •• Pb.D ......................................_..... __ ... _........... _._ .......Dea.. alld Direotor
ARGICULTURAL ENGINEERING OEPARTMENT (1,,11I.lIon)
GBORflV, E. 1'. 1IlfiTIl, O.F. •• n.v,n.t ............................................. __ ..... A..... lcultu ... l Rnltin ....
IIAROLD 0. SOBWALEN, B.S.In» E., )I.B.l1I O.E.._ ........ _ .. .Aaoc:l.t~ AtrrI~Ult"T"1 Rngineer
AIITI!UR n. OAR"-S, ~.S ............. _ ............... _.Fleld A..iotant I.. Irrigatlon Bnd H()rt;cultur.
BOTANY DEPARTMENT
JOm: J. 1"itoRNREII, n.S., A M............... _._ .............................. _ ...................... _ ...... Ilotan;.'
OAIRY DEPARTMENT
WALn:1I is. CUN~DWn"M. M >; ............................................................... 1131.)· ilushnndmall
RIOHAIID :'<. !)"V1S, M..!;..........................................................AIA<l(!Jatf ])~'"Y llu.lmndmKII
P~NT BREEDING DEPARTMENT
WALKr-:lI K IIlt'''Y. M.S .................... _........... _ ..................... _ ....................... rl."t llrt'f'der
ELIAS 1l. rREIISI.t;Y, M.S_ .................................. _ .. _.......................A •• o~b.te 1'la ..1 lireedeT
ENTOMOLOGY DEPARTMENT
ClIAIILg:s ". YURIlIES, n.s., (·11.1) ....................... _ ...... _...... _ •••. __ ................. En!omol<llrI!1
LAURt:KCF: I'. WEHRI.F., ~I.S., l'h.I) .................................................... " ... i~tn"t Bnlo11,,,lolI"l,.
HORTICULTURE DEPARTMENT
A1.L~:!>1 F. KIS:O:l:-:~)N, M.S ................................................................................... itortlculturi.1
UAVIn W. ALI!IWT, ll.!'i .................................................... A"""dD(~ II"ni~ul!u.h<t (I'hoenix)
MALCOLM r. WII'" RTON, ~I.S •• _._._ .......................... _ ....................... Aa"latant llorticulturlr\.
AGRONOMY DEPARTMENT
RAI,I'" 5. IIA\\'KI:O:S, )[.5 ................ _ ....................... _ ............... _.............. _ ....... A\m>lIoml.t
STASI.EV 1'. CLA 11K, B.S.._ .......... __ ..... _ ....... _ ...... _ ... _ ....................Anlstant Al(l"Onamlat
IAN A. BRIGOS, U.II ................... _....................... _ ............ _ ................. A•• Istanl AgrOl>Oml.t
GEORGE 11. SERVISS. ll.S .................................................... Rl'>Ie.rcb A"1<I"Unl In A~ronom,.
CHARl.ES HOBART, M.8. .............. R..""rcb A.. Istallt In AlfI"OIIa,n,. and lIorticulture ()h.... )
ANIMAL HUSBANDRY DEPARTMENT
t:RY.;S·1 Fl. t:;TA~LF.', M.S .......... _ ....................................................... Allhn.! n""bandma"
WII.LT.HI F. J)lORSOS. M.S ....................... _........................... A•• ;••• nl Animal lIusba"dn>a"
'KENS"ETH P. Pl0KRF.LL, B.S. ......................... __ ._... Fleld InVt"I;~at"T I" Animal Husbandtt
PLANT PATHOLOGY DEPARTMENT
JAMES G. BROWN. U.S., Ph.D ................ _ ... _.... _ ... _._ .... _ . _ .......... PI.nt Patbolog:lot
RUBERT B. STREETS. K.S.. Pb.D ............. _ .... _ _ .... _ ..... _ .. A•• O<!!.tf Pla"t PathoJOgllt
1I11,TON M. EVANS, M.S. __ ... _ .. _ .. _...... _ ............... R~."'rcb A•• I.t.,,1 In I'Jant l'~tholOlY
AGRICULTURAL CHEMISTRY AND SOILS DEPARTMENT
I'AUL S. BURGESS, Itt.s., Pb D_._... _...... __ ... _.......... __ .......... _ .....Agrl""tt"...1 Ohemll!
tJAMES I!'. BlUUZEALE, B.S._............. _.. __ ... _ .. _.... _ ... _ ................ R_n ... b BI""heml.t
WILLIAM T. )I~OF.ORQE, M.S ........... _ ..... __ ........... _ .................... R~.~arcb Obeml:ot In Rolli
TIlEOPRIL F. BURttRER, A.M., Ph.D ....... _ .............. _ ..... _ ................ _ •• Phr-ll1al Chemlot
HOWARD V. SMITH. M.S.... _ ... _ •.•. _.............. __ •• __ .......,,,."'''t.1I1 Agrl~UItD ... 1 Cb""'tot
ROBERT O. OREENE, M.S.... _ .. __ ............... _.•. _ .... _..... _ .... A .. I~I.nl Am~lI1tu ... 1 Chem,1t
MARION B.. ISAAOSON. M.S_.... _ ..... _............. _.... A..III.nt AICrt~u(t .. T.l Ch~mlot (Pboenb)
POULTRY HUSBANDRY DEPARTMENT
HARRY EMBLETON", B.8._._... _ ... _._. __ .. _ .... _ ... _ .. _ .. _ ......... _._ ...... Poult.,. R".bondmu
RUBERT B. RINDS. M.S..... _ ..................... ___ ... _ _ ._.. Aul ....... t Pooh.,. Ihub.ndm""
HUMAN NUTRITION DEPARTMENT
MARGARET OAMlIAO.l( R)lITH, A.)I., Ph,U_ .......... _. __ ............ _........ _.N"utrftIOD Ohernllt
HABEL L. LYNOTT. lI.S .......... __ •• __ ._... _ .. __ .. _ •• _ ....... R... earch Allut ... t til Nutritio:a
RANGE ECOL09Y DEPARTMENT
WILLIAM G. lIcGINNIES. B.S_. __ . ____ ... __ .... __ ............. _ ... _ _ .... Ranp Boolol1bt
-I .. coopentlon with th~ Sew Mp~~o A~riMlltunl El"perlmenl Sblilua aad tile United state<>
i)epl.rtmenl 01 Aln"lcultu ..... U"reau 0' An!n,.1 In,luIIT)'.
tlb eoopeTl>lI"" ",Itb United SUU. i}epartment 01 An]ealtun, Bu..... 0' PInt ladUlI.,..
CONTENTS
Introduction....... _.....................
......... __ ................... _....... _... _.......................... 419
"Caliche" ...... _.. ....
__ ............................. _........... _.... _............................. _....... 419
Caliche and Hardpan .............................. _.... _............................. _........... _... __ .... _............. 419
................ _._ .. _..... ____ .................... _.... _....... __ .. _ 420
Occurrence of Caliche ..................... .
Formation of Caliche ...... .
....... __ ......... _................ _..•... _..."_.... _..... _.... ~ ....... 420
Stalactites and Stalagmites......................................................... _.................................... 423
Types of Caliche................. _......•................. _........................•.................. _........................ 424
Movement of the Hardpan.......................................... _.... ~ ........................................... 426
Effect of Plant Roots lIpon the Formation of Caliche................ ~ ... _........................ 427
Formation of Calkhe ill Soils With a Water Table Near the Surface.................. 427
............................... _..... _.......... __ 428
Caliche Cement upon Rock Surfaces ....... .
Caliche in Crevasses._..................................................................................................... 429
The Hard Cemented Caliche of the ).Ies<"l L<"luds .......
. ............................... 429
Character of the lInderp,round \Vater Ilear Tucson ...... .
. ............................. _ 433
Separation of Calcium aud Hagnesium.
.......................•......•........._ 435
.................................................... 436
Pebbles upon the Surface of Caliche ..
Caliche Prouably Formed ill Lakes or Pools .............................
.................... 437
Caliche of Org<"lnk Origin...................... .
......... _............................................... 439
Conclusions .................................. .
.................................................................. 440
!}ihliograpIIY·······························
. .............•.........••.....•......................... _......... 4411.
ILLUSTR.\TTONS
Fig. l.-Illustrntiull showing apparatus used in making a core of caliche "._..
Fig. 2.-Tllt1StratioIl showing the formation of stalactites and stalagmites in
CaveInls................................................. __ .......................................................,...
Fig. 3.-Illustratir)Ji showing the crossbedding of caliche with other strata....
Fig. 4.-TllustratiotJ showing a typical caliche profile .............................................
Fig. 5.-IlIustration showing a piece of caliche capped with sheets of dense
calcium carbonate. The spaces between the sheets were filled with
10= and sand......................................................................................................
Fig. 6.-Il111.~tration showing a piece of caliche strattlm with pebbles cemented
upon the sllrface. Natural sjze....................."" ........ ~ ... _... _.... _.......... _._._.
422
423
424
431
433
437
TARLES
Table I.-Analyses of Santa Cruz Underflow........................................................... 434
Table !I.-Analyses of Rillito Underfl.ow .............................................. _.................. 434
CALICHE IN ARIZONA
By
J.
F. DREAZF.ALF. AND
H.
V. SMITH
T~TRODUCTION
Inquiries rel~tive to the origin anel nature of the lime hardpan, or
caliche, which is found widely distributed in southern Arizona, are
often received at the Experiment ,station. The mesa lands between the
Santa Cruz and the Rillito rivt"r<;, Ilear Tuc~on, and the same type of
lands near Phoenix, offer excellent examples of the occurrence of this
formation. These c:tlichc hed~ not only e"cite the interest of the tourist,
but they are also a matter of mnch importance agriculturally. They
are often so impervious as to prevent the penetration of water into the
soil, and are so deme that it is oftep nece~sary to break them by blasting
before trees can be planted.
The object of this bulletin is to e'(plain the chemical and physical
nature of stlch deposits, and, if possible, to describe the different conditions under which they were formd.
"CALICHE"
The meaning- of the tenn ·'Caliche" is not very definite. The word is
of Latin origin; Calx, meaning lime, was used originally in Spain to
designate crusts of lime which flake from plastered walls, or pebbles
burned into clay brick. It is sometjme~ applied as a name for cracks
which form in pottery.
The term was carried to Chili, Peru, ami. Argentina by the Spaniards,
and there applied to the deposits of sodium nitrate, or saltpeter, either
on account of the presence of lime in these heels, or of their resemblance
to beds of lime hardpan or tme caliche. The early Spanish settlers in
the Southwest applieel this term to calcareous hardpan, and, in Arizona,
the term "caliche" is now used almost exclusively to designate such
formations. Caliche and hardpan will be used as synonomotts terms in
the following discussion.
CAI.TCHF. AND HARDPAN
Caliche mav he defined a~ a true hardpan. How/;,ver, the term "hardpan" is very i~definite also. To the ordinary individual this term applies
equally as well to a puddleri. condition of the clay subsoil, or plowsole, as it
does to the worse types of hog iron formations, that are common in the
420
E){PERIME.VT STATIO.V BULLRT/.V ,Yo. 1.'l1
lowlands of the N orthwe~t. It must he remembered that the formation
of caliche and other hardpans is brought ahout hy the solution. the
transportation, and precipitation of comf' cementing material. In the
bog formation above referred to, this Ct'll1C'llting material iEl iron, in certain other sections it is silica, nnu oC'ca~ionany it may he organic matter.
Iron, silica, and organic hardpans 'l('cur in humid regiom. hut caliche, or
calcareous hardpans. seldom occur uutside of arid or <;('mi-arid regions.
The cauche in Arizona is alway" calcareous.
OCCURRHNCE OF C_\UCTIE
Caliche usually occttrEl either as ~trata of thin ~h('ets of fairly pure
calcium carhonate, or a~ a conglomerate. that i~ fl.". ;,and, !:;ravel, etc.,
embedded in calcium C<1.rb0113tc, or a ... a mb..ture of ltl1c(,llwnted material.
Caliche is a natural cement, and it:': stnt('ture depends upon the conditions under which it wa<; formed. The pttrity of the calkh(', or its percentage of carbonate of lin1(', v<Lrie<; widely, depenrling upon the amount
of foreign material which it contains. It seldom occurs a<; a regular,
horizontal stratum, but in irregular la),e1"<;, varying from a fraction of
an inch to many feet in thicknc<;<;. Caliche may app('ar upon the surface.
but is more often covered by a layer of soil. It is oft(>n continuous oyer
many acres, and conforms roughly to the contour of the land. In
thousands of place~ it is exp(lse<i by railroad cuts, wa<;he.';. well.';, cellars,
etc" where accuratc cross-.';ection<; may he fltttdied.
Caliche may occur upon the hills alf,o, n,> a coating of fairly pure calcium carbonate over vnlC<1nic rock", it may occur as a ,'dn in crevasses,
or it may occur in <;hec-t<; oYer a valley fill. Tt ON'tt1":': only where there
has been a supply of calcium carbonate in a solution of carhon dioxide,
and where the drainage is not ~ttfficient or rapid enough to remove the
water. In all cases there must be an adequate <;upply of cakiuOl carhonae, or limestone. Thi~ usually comes from til€' Paleozok limestones
that are widely distributed ill ~otlthern Arizona, from igneou.'; rocks, or
from the soil. The gravelly mesa soils where caliche often occnrs. usually
contain 5 percent or more of calcium carbonate.
We have in southern Arizona man~' of the conditions that arc essential
to the formation of caliche, namely, a very dry atmosphere, rapid evaporation, light rainfall. an rthttndant ~l1ppl)' 0 f calcium carhonate. in many
sections a high water-table, and Hudergrrll1nd water 'which nearly always
contains calcittm bicarbonate.
FOR11ATION OF C \LICJT!;
As mentioned before, all form'> of caliche involve the solution, transportation, and precipitation of calcium carbonate. The formation of
C1LlCIiE IN .1RIZON.j
421
caliche is, therdore. largely a chemical phenomenon. The calcium carbonate mar he di"~olved and predritated in the same stratum, as when
a bed of caliche i:- broken 11p and recemented, or it may be transporte(l in
solution Qvt;'r long distance". and pre-cipitated.
In pure distilled "·ater. calcinm carbonate is soluble only about 8 parts
per million. but in colr! water that has been saturated with carbon dioxide,
its solubility is increaser! a hundred-fold. or over 800 parts per million.
This increase in <;oluhility i ... dne to the pre.,em'e of carbon dioxide, which,
when combined with \Yater. form~ carhonic acid. The carbonic acid, in
turn, dissolves the calcium carhonatc and forms calcium bicarbonate.
Solutions of calcium bicarbonate are fairly stable and. as long as the
carbon dioxide remains in solution, the calcium carbonate may be transported great distances as the hicarhonate.
The precipitation of calcium carbonate' from such solutiom is brought
about in two way". either hy the evaporation of the water in which it is
dissolved. or hy the IO~li of carhon dio'(ide by which it j<; heir! in ~ohtti()n.
Carbon dioxide may be driven off from stich solutions by boiling, by
merely agitating tht:: ~olution vjg-orotl~l:', hy n relief in pressure. or by
the action of plants.
The fonnatioll of calicTl(' may he either :l. "liow or a fairly rapid proces~; the density depemh; Jnl'gely npon the ndt: of precipitation and the
amount of foreign material in the ma~s. The dense. impenneable types
which lie deep in the alluvial material filling valleys and basins are probably very old. while the "ofter types which tie near the surface in the
flood plains. may he of recent origin. 11any cases are reported in Tucson, where pieces of hrick and gravel have become cemented together in
a few years. or wh€'re a well defined stratum of caliche has formed a few
inches below the surface. in a lawn that has heen watered regularly. No
evidence in the fonn of fossils has heen fonnd in caliche that would indicate a great age. geologically. Tt has a1\ heen fonned in the present era.
The position. structure. and chemical composition of the different
fonns of caliche indicate ckarly that no one hypothesis can explain the
origin of the different types. 'The authors have found that nearly everyone attributes thi OCCllrrenc{' of caliche on the hills to the same cause or
causes that prodt1cen it in the ,'alleys, and thi~ assumption has led to
much misunderstanding. In the following discussion several types of
caliche will be considered, and a reasonahle e"qllanation for the fonnatioD of each type will h{' given. However. caliche occurs in all grades
and mixtures. A very old and impenneable stratum may be broken up,
and r('cemented in a few years. 'The re-ad<-r i~ cantioned, therefore.
against drawing condu'=.ions that may hI"" too (''<aet.
Recently the authors produced a column of caliche. a~ a conglomerate.
by means of the apparatus shown in figure 1.
422
EXPERWENT STATIO!': BULLBTIN So. IV
A
- - -5
- ---c
\~ _ _ _ _~,L _
_
-
- - --0
L~fW~~~W~~h?0~!0~!0~0~W&;~~~~?~h~~~~~~~"~%~~~~~~~j - - - -~E
Fig. l_I1Iustrat!Oll showing apparatus
ll~ed
in making a core af caliche.
A supply of a s(llution of calcium bicarbonate was made ev~ry day, by
bubbling carbon dioxide intn cold water which contained a quantity of
finely-divided caki11111 c(trhonatr. Thi~ ~nlt1tion v, as then placed in the
reservoir, A. and allowed to drip slowly into a funnel which carried the
solution down into a small cloth h..'1g which had been filled with a mi>..'1:ure
of sand and small gravel, H. The bag was hung in an electric oven. C.
which was heated by a hot plate, R The door of the oven was kept open,
G.1LICHE IN .-lRIZONA
423
so that the temperature on the inside registered about 90e C. The flow
of the solution was regulated <;0 that a<; much as possible was evaporated
within the mixture of sand and gravel. The overflow was collected in a
pan, D,
,\fter running' a few days, the column began to harden at the top, and
after several we<'ks, a core of moderately hard caliche, that resembled
the natural produd. wa~ ohtained. This e:o-.periment is described in order
to empha~ize the rapidity with which caliche may be formed.
A
c
D
vrr
,
I
Jl1il:
Fl!/.. 2-ruustratt'11l showiug tbe fommtiQll of
~ta!actites
I
I
l.:,
and stalagmites in caverns.
ST. \L. \C'Tl'l'ES .\..\'D S1'.\'L. \G~[I'rES
. \. familiar example of the &olutioll and precipitation of calcium car~
bonate by percolating \\ ater i<; seen in the formation of stalactites and
stalagmites in the caverns that are common in southern Arizona and in
all limestone regions. \Yater, when charged with carbon dioxide in
percolating through the ::.oil, diq<;oh'es a certam amount of calcium carbonate. \Vhen this water (lrips through the ceiling of a cavern, either
the water is evaporated. or the {'arj'oll dioxide is driven off, and a precipitation of calc1l1m carl>onat(' take~ place. If the cavern is relatively
dry and well ventilated, the water i~ often evaporated at the ceiling, and
a ~talactite will be formed: Fig. 2 (A). On the other hand, if the cavern
is humid, the water may drop to the floor, lo",e part of its carbon dioxide
by concns::.ion and heat. and pre{'ipitate the calcium carbonate as a
~talagmite. Fig. 2 (Hi . .-\ stalagmite weighing many tons. may form
from a stalactite no larger than a pencil. I f conditions are such that a
fairly moderate and uniform evaporation takes place, the stalactite and
424
EXPERIMENT STATlO.V BULLETIN No. I?I
stalagmite may be of approximately the same size, Fig. .2 (C). If precipitation continues long enough. a solid column ma~ be fonned. Fig.
2 (D).
Stalactites and stalagmites are usually very pure forms of calcium
carbonate, for the reason that the lime hal> been precipitated from filtered
water, in the absence of foreign matter, Nearly all caverns \\ere formed
originally as many are now belPg built up, that is, by the dissolving
action of water which is partly charged with carbon dioxide.
TYPES OF C \LICHE
In many sections of the State a type of soft caliche is found which
ranges in thicknes~ f rom a narrow band up to c;everal feet, and is usually
covered by a layer of alluvial soil 2 or 3 feet in depth. Under field condihons, this caliche is pemlcable to water. and is soft and pliable. It
usually consists of about .10 percent calcium carbonate, and 60 percent
of sand, clay, silt, and other material. Where no cementing action has
taken place the lime carbonate exi"t!> in a finely-divided condition.
If removed from the soil and worked up with a limited amount of
water, the mass becomes plastic like putty, \Vhen the mass hardens
upon exposure it become~ vcry den!>e, and may be used as a surfacing
material for roads, or for building material.
The prehistoric rnim of Casa Grande, near Florence, are composed
largely of caliche, whIch was dug from a nearby pit. moistened, and
moulded into form~. These rt1in~ have been standing exposed to the
elements for many centurie<;. and many of the walls are stiU in a fair
state of preservation.
ca.l,d" _. -;
,.
••••
r.: .
.- ,
~:;~.
/0:
'
folg 3.-T1Iu~t ...,dlOn sho\\mg the cro~,~ddmg of caliche wltll other shata
Evidently caliche of thiS h PI" was not laid down, a~ such, by desert
dunng the ag(' III which the '"alley fill deposit was being formed;
that is, the carbonate of lime would not have been brought down in suspension, as was the clay or ~tlt, and deposited in a stratum over th",
surface. This fad l~ llrc'nght ant clearl~ by the pOl>ition of the caliche
stream~
CALICHE IX .1R!ZOl·;.4
425
in the crossbedded material, Fig. 3. The caliche stratum does not necessarily conform tf) thl' strata o{ silt or day, but often cuts through such
strata. The position of the caliche is more determined by the distance
from the !'lurface of the '3oil, than it is by the presence of strata of silt Or
day. In many localities, one is impressed with the uniformity of the
depth of the hardpan from the !'lurface.
'While semi-arid, southern Arizona is not a desert, the mean annual
precipitation varies from IOta 15 inche~, although great deviations froUl
the mean occur. Tucson for example ha~ a mean annual precipitation of
11.51 inches, ret in 1905, 24.17 inches of rain fell, while in 1924
only 5.16 inches were recorded, so for a time each year the soil is
wet to a depth of 2 fet't or mort A <;suming that a certain soil has a
water table below 20 feet. or too low for capillary pull to be a factor,
during a part ,)f tlw ) ear there will be a well defined moisture plane, or a
horizon, where the: mOl<;t <;oil of the <;urface shades off into dry soil.
Assuming that a <;oil has no hardpan, htlt that it contains 5 percent of
calcium carbonate, if no ero<;ion or deposition is taking place, the rain
water which i<; chargl'd with carbon dioxide will penetrate the soil, dissolve some calcium c"lrbonate, and carry the di'>501ved salt downward
until a state of moi'lttlre equilibrium i.:; reached. The water v;rill be
evaporated largely in place, and the calcium will be precipitated as
calcium carbonate, or caliche, instead of being drawn back to the surface
by capillarity. as formerly supposed.
The downward movement of water into a soil is caused by gravity
and other forces. 'Vhen the~e forces are at equilibrium no movement of
water is possible. .At a depth of::! feet, in a soil at equilibrium, the upward movement of water by capillarity is negligible, so the rain water
which has penetrated to that depth, either must be di'ltilled by the heat of
the soil. or it must be abs(1rbed by organisms, or by plants for purposes
of trampiration. In either ca<;e, some calcium carbonate will be precipitated at a depth of 2 feet from the surface of the soil.
The next rain may cnrry more calcium carbonate down to the same
level, where it WIll be precipitated. If the movement of water is continually downward, the movement of the calcium carbonate will be
downward also, and thus a stratum will be built up at the lower edge of
the moisture plane. Under natural conditions, as long as the stratum
remains soft and pen11eable, it usually remains in the horizon that marks
the extreme penetration of water.
The penetration of water controls the position of the hardpan. but 1h(>
hardpan may have little or no effect upon the penetration of water.
The hardpans that are common through the Great Plains, or the area
stretching from Texas to North Dakota, have been formed, largely, in
this way.
426
EXPBRWEXT W.-:l.TIO.V BULLET].V .Vo. i3[
In the soil, limestone mar he reduced to a \'ery line state by atInos~
pheric agencies, in which condition, it is ea"ily held in suspension, and
may be transported hy water, and thrown down as a stratum without
ever going into solution. After stich a stratum is fonned, it may be
cemented together by calcium C-.1.rl.>onatc inio a compact and impermeable
mass by the solution and precipitation processes described already.
MOVEMENT OF THE HARDPAN
As mentioned before, hardpans, as long as they are soft and penlleable,
occur at approximately the same depth in the soil, that is, at the lower
edge of the moisture plane. In the Great Plains, sometimes a hundred
ieet of soil has been eroded from the surface, yet the hardpan remains
in the same relative po~ition to the );tlrface of the soiL
If the hardpan has been formed hy the evaporation of dowllward~
moving water, and equilibrium has been established in the soil, a soft
stratum of caliche, probably 8 inches in thickness. would be formed 2
feet below the surface. If erosion should remove one foot of soil, equi~
librium would be upset, and the tendency of the moisture plane would be
to move downward. The T<.in water, charged with carbon dioxide, per~
eolating through the soil might reach the upper edge of the hardpan l1n~
saturated, and would dissolve some of the calcium carbonate. If the
hardpan is permeable, the ~att1rated solution would move down through
the stratum, and appear at the lower edge where it would be evaporated.
The dissolved calcium carbonate '\'ottld be precipitated at the lower
edge, so the caliche ~trat111n would be formed from below, and remain
at approximately the flame di~tance frOIll the surface. It would c011tillue
to move downward as fast as ero~ion removed the surface soi!.'"
However, if more debri~ j~ deposited uj)on the surface. the hardpan
would not move upward, but wotlld remain stationary, and a second
stratum of caliche might h(' fonned above the first by the evaporation of
water, which carries carbonate of lime. ,such a condition may be seen in
a great many places.
In many places in the Great Plains, and other regions of light rainfall.
clay hardpans are found that are cemented with a very small amount of
lime, often less than 5 percent of calcium carbonate. \Vhcn floils with
such hardpans are placed under irrigation, the moisture plane is lowered,
and the hardpan is often grarlnaily disintegrated. Many such hardpans
soften up during period~ of winter rain-c;. and reappear during periods
of summer drought.
"'The idea of a mo\'uhle hardp:1I1 was ~u~~estt!(1 hI" ).fr. E. C Chilcott, of the
.
United States Department of .-\gricultl1rc.
CALICHE IS ARIZONA
EFFECT OF PLAl>;T ROOTS C'PON THE FORMATION OF
CALICHE
The part that is played by tral1gpiring plants UpOll the fonnation of
hardpan is very pronounced, and is shown almost always wherever the
caliche is exposed to view. Often the position of a root may be traced
by a well defined zone, or incntstation, of fairly pure calcium carbonate.
The authors have found such crusts that run over 70 percent of calcium
carbonate, while the soil, a few inche<;' from the root would analyze less
than 20 percent.
'When plants are growing upon the ,surface, the loss of water from the
lower depth of a soil, is ltsnally due largely to transpiratioll. In the
process of transpiration the pJant takes up water and leaves the dissolved salt, which is precipitated. The small lumps of soft caliche, which
are so common upon the m{'sa~ that are coyered with creosote bush, are
often formed in this way. \\Then examined closely these lumps will be
found to contain dead roots, or small holes where roots grew formerly.
Usually plant roots follow moi~tttre, and do not penetrate a soil' below
the lower edge of the moistnrc plane. 'fhe position of a caliche stratum
which has been formed hy plants, may corre~pond to the position of a
caliche which has been prodnced by the evaporation of water by heat.
The formation of a str3.tttm of caliche hy plants j~ always hastened by
the evaporation of water from the ~urface of the soil.
T"
FORM.\TION OJ' C\UCHE
SorLS WITH A WA1'ER
'fABLE NEAR THE SURFACE
In the foregoing di~cus~ion only caliche that has been fanned by the
precipitation of calcium cn.rbonate {rom downward-moving waters, has
been considered. The hardpan, in all such cases, marks the extreme
penetration o{ water. In all such formations the movement of water by
capillarity is of little importance.
However. in many parts of .'\ri7ona. e<;pecially in the flood plains,
there is at present or there has ('xisted in the past, free unrlerground
water, or a water table, within a. few feet of the surface. Under such
conditions, the capillary movement of water is of great importance.
While water does not move by capillarity to any appreciable degree in
a soil at its field-carrying capacity, in a !.oil that is in contact with free
water, that is, in a ~oil with a high water table, the upward movement by
capillarity m:Ly be pronounced. Nearly all underground water in Arizona contai05 calcium bicarbonate. This may he carried upward by
capillary water to the extent of the capillary pull, which will amount
to about 3 feet in a sandy soil. or to .5 fect or more in a clay. Here
428
EXPERLIIENT ST.rnOX BULLETIN No.
IiI
the calcium carbonate i~ precipitated by the agencies which have been
described already, and a stratum of caliche will be formed 3 to 5 feet
above the water table. Such a conditioll will exist ,,-hen the movement of water is continl1a11y upward, and caliche may be fanned,
although the sur face soil may never be wet.
In all region~ where caliche occurs, however, there is some rainfall.
and the carbonated rain water with its dissolved calcium bicarbonate will
move downward until it reaches a state of equilibrium. The precipitation of the calcium carbonate may then occur at, or above, the horizon
which marks the precipitation from the water that ha~ been drawn
up from below. In stich case" caliche may be formed, either in a single
stratum from both ascending and dCM'enrling waters, or in two or more
strata,
It will be seen that no one theory of the formation of caliche can
be applied to all cases, and that more than one factor is always operative. A certain stratum of caliche might have been fanned by a
certain set of factors, yet another stratum within a few incheq of the
fir~t, might have been fomled by a different c;et of factor..;.
Under conditions where cali.che is forming from 11nderground waters,
by evaporation, jf the stratum is not imperviotlS, the sudden lowering
of the water table may cause the formation of another stratum below
the first. However, if the first stratum becomes cemented and impervious to water, no second strahtm is likely to fonn, In other words,
precipitation will take pi<1ce only where there is evaporation or a release
of pressure.
CALICHE CEME)JT UPON ROCK SURF.\CES
In many place~ in Arizona, a crt1!>t of fairly pnre calcit1lu carbonate,
often of recent origin, may be seen as a coating on many kinds of rocks.
This condition jq very noticeable upon the volc-anic hills south of TUCqOll.
and has been described by Tolman (5). 'fhe cement, or caliche. i~
deposited usually upon the rock surface, in layers of less than a centimeter in thickness. It occnrq in the draws, Or ravines, which run
down the hills, rather than on the exposed ridge~, and spreads out as
the base of the hill i~ reached. Often many sma.ll pieces of rock are
cemented together in the form of a conglomerate.
Upon the volcanic hill~ thr-re is no water table, and often little or
no soil. The caliche coulrl not have been formed from underground
sources, nor could it have bero leached from the ~0i1 and reprecipitated
as described already. The ba"a1t~ of these hill~ are very porous, and
many of the cavitie~ were filled with calcium carbonate and calcium
~t1lphate. Tn the proce~q of the formation of caliche, the~c ~alts were
CALICHB IN ,JRlZONA
429
leached from the rocks on the higher ridges by rain water charged
with carhon dioxide, and the calcium bicarbonate was carried in solution down "lope into the ravines and small washes. Here, running in
thin sheets over warm rocks, some evaporation took place, much carbon
dioxide was lost, and calcium carbonate was thereupon precipitated
in thin layers over all of the material which bappened to be covered
with water:- 'l'he calcium sulphate was carried off by the runoff
into the Santa Cl"tlZ River.
Occasionally, all the "lope, a rock of irregular shape may be found
covered partially hy other rocks, and between these rocks cavities of
considerable size may occur. The rain Vlater, from which calcium
carbonate was precipitating. has trickled into these cavities, and often
hundreds of small Rtalactites and stalagmites have been formed upon
the inner walls of these miniature c.1.ves.
C.~LlCHE
IN CREVASSES
Caliche often occurs in veins in rock ma!>Res. where fracturing has
produced crevasse" or fi"'lurcs. These "eiM of caliche may be horizontal
or upright. or they may be tilted at any angle. The precipitation of
calcium carbonate under such conditions was much the same as that
described in other cases of caliche fOT'IIlation. Water. carrying calcium
bicarbonte, penetrated these cavities where evaporation took place, or
where carbon dioxide was lost and calcium carbonate was precipitated,
The purity of the caliche formed under such conditions varies with the
amount of foreign material enclosed. When precipitated between
igneous rocks, for example, it is u,:,ually very pure.
THE HARD CEMENTED CALICHE OF THE MESA LANDS
Probably the most interesting type of caliche ill Arizona. is that
represented by the caliche which occurs in successions of hard, cemented,
impermeable strata. that are very much in evidence upon the mesas
in southern Arizona. In that section of Tucson, which iR built upon
the mesa, practically every fence post is set in caliche. In digging a
cellar or ces"pool, or in laying a pipe line, it is usually necessary to
Jri11 or blast through a bed of this material, ranging in thickness from
one foot to 10 feet or more. Snch caliche covers an area of probably
300,000 acres in Pima county alone. equally as much in the Salt River
\. alley, and al~o large areas in other parts of the state.
Farming or gardening upon a ~oil which is covered or lImlerlaid
"This is the opinion of Dr. R. H. Forbes.
430
EXPERIMENT STATIO},' BULLETIN No.
1~!
by such a formation i<; Yery difficult. Neither plant roots nor water
will penettate certain of the strata. If a fntit or shade tree is to be
planted, it is customary t-o first break the caliche by blasting or drilling,
and then to dig a large hole, 3 feet ~'1uare or more, which'is filled with
good soil. The tree is then planted in this good soil.
As this type of caliche is of so much economic importance, a detailed
description of its u~t1al structure, its physical and chemical composition, and the most reasonable hypotheses of its origin will be given.
W. P. Blake. (1) fonner Director of Arizona School of Mines, at
the Richmond meeting of the Institute of Mining Engineers in 1901,
stated, "There has been much speculation in regard to the origin of
caliche. It has been generally assumed to be a. deposition from some
ancient lake, or body of water, once covering the area in which it
is found. But such a theory is untenable when all the phenomena
are considered. The formation is clearly the result of the upward
capillary flow of calcareou<; waters. induced by constant and rapid
f.vaporation at the surface ill a comparatively ninle~s region."
Tolman, (5) in discu<;<;ing the geology of the volcanic hills southwest of Tucson qnotes the opinion of Director Forbes of the Arizona
Agricultural Experimellt Station to the effect that the two constituents
of caliche, colloidal clay and carbonte of lime, one carried in suspensions
and the other in a ~olution of carbonated rain water, penetrate the de~ert
soils to a depth marked by the penetration of water from an occasional
rain. At the general average level at which the wetted soil dries
out through the drying action of arid atmosphere, a more or less
compact stratum of caliche is formed. When the surface is filled
from time to time. new caliche Gtrata are fanned. Tolman also r('cognizes the effect of the upward movement of underground water.
Guild, (3) attributes the occurrence of layers of caliche near the
surface of the soil. to the evaporntion of meteoric waters it! situ. while
deep layers are formed by the evaporation of water, which has been
brought up by capillarity from underground sources.
Lee, (4) in discussing the underground water of the Salt River
Valley expresses the opinion that mnny of the caliche layers in this
valley were formed by the upward movement of ground water which
contained calcium bicarbonate, and the suhsequent evaporation of this
water below the surface of the soil.
The opinions of these investigators represent the prevailing opinion~
as to the origin o£ caliche. Nearly everyone attributes the formation
to one of two factors, either the evaporation of descending surface
Water, or to the evaporation of ascending ground water. Blake mentions,
but discounts the possibility of caliche being formed in old lakes.
There is no doubt but that many of the factors that operate in the
CILlCHE IN .1RIZOA·A.
431
formation of caliche were active during the era in which this particular
type of caliche was formed. Small nodules of soft caliche, which have
been formed by roots of plants during recent years, are often found
imbedded in dense, cemented ~trata. of evident great age. However,
it is the opinion of the authors that the caliche, which occurs upon the
mesa land around 'rucson, was deposited from o;m~ll lakes, or playas,
or from shallow pools of stagnant wnter. The precipitation of calcium
carbonate was probably hastened by the presence of algae and other
water plants in the'le pools.
E.t·pluHatioll. The percentages of CaCO. at the various
depths as indicated in inches
on the accompanying profile
are as fonows:
o -
6 -16.4
6%f=94.0
6~- 9+1--61.0
944- 10-11=76.0
1O}:4- 1314=50.6
1314- 16~=37.2
16%- 30 ===40.2
6 -
30 - 44 =10.4
"
44 - 55 =17.8
55-70=6.0
70 -82 =75
82 -94 =1.5
9-l- -124 = 00
124 -136 = 1.5
136 -148 = 0.0
148 -iS8 = 00
Fig. 4.-I!lu~tlation showing a typical cahche profile
.\ typical soil profile of the Pinal ')eries, the soil type on which the
University is built is shown in figure 4. It is from a cut 158 inches
deep in the
Encanto Estates east of the City. 'fhe surface 6 mches
of soil is a loamy sand containing 23 percent of material not passing
through a 2-mm. sieve. This coarser material has the appearance of
lime concretions btlt a close examination ~hows them to be only limecoated pebbles. Immediately below this loose ~urface material, as
m
432
EXPERIJJENT STATION BULLETIN No. 131
shown in figure 4, is a dense layer of very pure lime three-fourths of
an inch in thickness capping a 3-inch layer of softer caliche which
has a lower lime content. Another half-inch of very compact material
is found under this chalky layer and as in the upper compact layer
its lime content i<; higher than the less den<>e strata above or below
the one extending 2;1 inches below. At a depth of 13 inches a little
gravel appears to be mixed with the lime and the whole is cemented
into a hard, solid mass.
The percentage of sand and gravel increases slightly to a depth of
30 inches where a vein of gravel is encountered. These lime-andgravel mixed deposit<; contain in the neighborhood of 40 percent lime
which is the maximum clmonut possible in tbi$ type of soil if only
the pore spaces are to be filled.
The gravelly strata which underlie the ca1iche~cemented layers be~
come less rich in lime with increased depth until at the 82-inch depth
only 10 percent of lime is found. Below this only traces of lime occttr
to the bottom of the hole, 158 inches below the surface. The log of a,
well drilled to furnish water for the estates $hows a repetition of these
caliche strata down to a depth of at least 71 feet, and possibly more,
although caliche as such is noi. indicated in the log below this level.
Such is the character of the soil in which this dense stratified caliche
is found.
As illustrated in figure 5, the strata occur usually as a succession
of compact ~heets, arranged one above the other in irregular manner.
and separated from one another by thin layers of soil or granular, earthy
deposit. The sheets of caliche vary from less than a millimeter to several
centimeters in thickness, and often a dozen or more sheets may occur
m a horizon of less than a centimeter. These thin sheets arc usually
impermeable to water, however, the whole mass, may be so broken by
fissures and irregularities in deposition that water may percolate the
soil.
The fact that these sheets of caliche are impermeable to water is
good evidence that they w('re not formed within the soil, either by
descending surface water, nr by ascending ground water. Assuming
that the evaporation of a8cendiug ground water fanned one very thin.
impermeable !>heet of caliche, thi.s sheet would effectively check
evaporation. and further precipitation of calcinm carbonate would be
checked. In order to have deposition continue, it would be necessary
to assume either continued evaporation from the surface or a reduction
of pressure. Often a ~tratt1m of caliche 20 feet thick occurring as a
succes!>ion of impermeahle sheets is found. It seems impossible to
believe that such a formation could have been built l1p frOIn below,
C.-iLJCIIF. I.\'
/k/X()S.'/
433
a-; outlined IJy Blake. If it had heen huilt up frolll l>elo\\". the caliche
probably woul(1 ha\(:, hn"n llIore or le.-;s ullliurm. rather than existing in
thin ~hl'(;ts ~ellarated by earthy material" If an impermeable stralUm
h:ul been formed from watl'r Ihat had riSl'lI from a definite level, the
sulN:quent 100\'l'ring I)f the t;d)11' wOlllfl !lot lw('essarily tend \0 fonn
it1lothl'r ~lrat\llll"
Fi..:.3. -lllustfatjnl1 ,h""illl! a IJil'n "i "alidw .. al'i'I,,1 with slw,,[, .. j 11<-11'" r.""lriu1ll
'"'Ifh'.na!.," '1'1", ~I';,n" 1"'lWwn lh,· ~Il<"d~ ",'n" lilh-,1 "jlh l"al11 and ,an'l.
TIll' a~~Ullll'tl(ol1 11':11 dIe calidll \Ia~ iflrn1l'd frrHll umkq.:ruund IliltlT,
rarril's \Iith it tht idl'a ur ;\ high Ilatn table, I'racticll1y 11ll' tllIl:,'
plan' wheH' r.";tllr1w r.";m h.' (I)fnw,l i..; at ur nl'ar the ~ttrfar.T. for IWfl'
I~ Illwn' 1~I'al")ralil'" takt."~ 111an', Ilr W1WH' ]IHS"llfl' Ilf carhl!!! Ilillxilk
i .. rdie\'ed, \ high lIall"r tahk· i~ f"I11I.1 frequentl.\' in th,· tloud piailh.
but it has hr.'e!! mally n·11111rit·s .. inn' wat,"r ha~ ri~,'n upon many of til"
tlIt'~a~ to a kn"\ wlwft" t-apiJ1ar.\ ],\11! to\lard~ thl' ~\1rfact' would I",
l,I1\TIIYl'" Frn- WaitT wO\1ld halT til "c(.'ur within :-: or 10 fWl oi th,
~\!rfa~·r.' hdof(" all_I "ppn-cia]'lt' r1l'I'" .. itiOlll IIf r.';j1ic!1{' ('oldll hi' ('x]l('cted,
('I1\1~\CT1':I~
II],'TIIF
'\E.\I{
1-:\IJ!~I~(;]{(ll'\I)
\\,\'J'i·:R
TIT~()\-
Ii til(" ralidw had hl'en f.. mll'd h.\ thr." t'I;!J)(,r;lli<ll1 of 1II1tkrgrll11!1d
Ilat,·r. lIlt' rariHmatl· ... 'Ii 1111'h Clkill11l :tll11 Tlla!.:lll·~il1111 lI'f,u1tl ha\'\:' 11<'l'11
I,n-npilaterl mIl. :1Il,1 1~1 ~lwh Cl ..e"" tht, ca1i(.'11,· l\flu1d r'.l1t;,ill cakilll\1
434
EXPERlJIEX1' ST.1TION BULLETI.\' No. IV
and magnesium in the same propurtion as these elements existed in
the original ground ,,-ater. Tucroo lies between the drainage basins
of the Santa Cruz and Rillito rivers, but the vohmle of both surface
and underground water is much gre<1ter in the ~a.llta Cruz than it
is in the RilHto basin. The ch('mical composition of the two uuderflows
is very different. The Santa Cruz sh,1.llow tl1l(ierflow as it approach('s
Tucson has a relatively high salt cont..-nt, and i,; .. hard," while the
Rillito underflow is 'lsnaIly low in total snlts, and is" sott."
In Table I arc shown analyses of the Santa Cruz ha"il1 water from
five shallow wells between ~an Xal'ier )'fission and Tttcson. These
wells were above, and 311 within 10 miles (If the city, where the \vater
table is about 40 feet below the surface. The results are expressed ill
parts per million.
TABLE L_AK:\LYS£S
Well
or S\l><·T.\ C1U:Z
1)
'T~o-m-1-"~"-'~..~-...-...-.. -..-...-+-3~7~6-1--Cj~--Calcium (Ca). ...............
Magnesium (:M:~). ...... .
bO
21
30
Ii
Bicarbonate (HCO.) .... _.
Chlorine ( ell ".." . ..........
240
42
144
2R
Sulphate (SQ,)... .......
102
157
UNOF;Rf1LOW
__3_11--;;;;:4;-~J_S_
6R()
112
240
56
278
7M
120
1560
150
336
70
285
312
1M
697
2C)11739
,I
~==~==~==~=====o=====-_-=-The average ratio of calcium to magnesium in these waters is 1.0
of magne~il\m to 1.2 of calc-inm.
In Table II are shown the analyses of water from five shallow wells
in the Rillito Yalley, ahoye Tucson.
TABLE TT.-A).TALYSES OF RILLITO Ul\'DERFLOW.
_ _ ~~ _ _ _ _
1_
Total salts. .. ........ _ ... .
Calcium (Ca).
Magnesium (MI!.). ... ......
Bicarbonate (HCQ,) .
Chlorine (Cn .... _..... .. ..
Sulphate (SQ,)...
Z2<~
75
()
120
21'
43
----;~ __ ~. __ '__ ~_L __ 5.' __
160
lR
352
57
3R4
45
Trace
102
Trace
16il
Trace
192
10
,~9
20
120
3R
Q7
26<'1
69
5
240
Trace
40
==
It will be Sf2'~n that the tlnde-rfinw in the Rillito ba.sin i~ very low in
magnesium, the average ratio ht'ing ahout 1.0 of magnesium to 15 or 20
of calcium.
Analyses of many samples of the r1eme upper Cntsts of caliche strata
collected from different place'S hetween these two drainage basins, show
that the caliche runs usually about 90 percent or more of calcium carbonate, and 1 or :2 percent of magnesium carhonate. Caliche of such
composition scarcely could have been precipitated from Santa Cruz
underflow as it exists today, if we m\1st assume complete evaporation of
the underground water. The caliche probably could have been precipitated from Rillito underflow, howevf2'r. if this lmrlertlow had existed in
CALICHE IX .JRIZONA
435
sufficient amounts. The possibility of a change in the underflow since
the formation of the caliche must be considered.
It will be noted also, that the waters from both the Santa Cruz and
Rillito basins often contain relatively large amounts of sulphates. A
completc evaporation of these waters would precipitate appreciable
amounts of gypsum. The '>heets of dense caliche however, do not ordinarily contain more than about 1 perc\",nt of gypsum. This indicates
either a partial rather that! a complete precipitation, or a condition under
which gypsum might hu\'e been precipitated, and subsequf:'ntly leached.
The dense sheets of caliche show no indications of leaching.
In the same way, many objections are evident to the hypothesis that
the densc, impermeahle caliche was formed by the evaporation of descending surface water, as outlined by Forbes and others.
Many samples of the thin, dense sheets of caliche have been collected
recently at depths of one foot or more below the present surface of the
soil. These sanlples run as high as 90 to 94 percent of calcium and
magnesium carbonates. The other 8 or 10 percent consist of clay, iron
oxide, etc. The purity of these samples indicates that they were precipitated upon the surface, from relatively clear solutions, and in the absence
of appreciable amonnts of materhls su-ch as sand, gravel, etc. If the
precipitation occurred within t!'te body of the o;oil caused by the evaporation of downward moving water. the caliche would have filled the pore
spaces and :"urrot1l1de(\ these earth" l11nterials. It would have be{'l1 a
conglomerate, tl.nd impure to the c':tent of the foreign matter. If caliche
consisted of large crystals of calcite, it is possible to assume that all
foreign material had been pushed aside during the process of crystallization. But the caliche does not exhibit the crystalline structure of calcite. it occurs more like a cement, and suggests a rapid development, in
comparison with ordinary s\o\\', geological processes.
It appears safe to assume that. if precipitated within the soil mass, the
purity of the caliche would not have exceeded that represented by the
pore space of the soil. If precipitated upon the surface from still water,
only those impurities which were held in suspension would be included.
These impnrities are largely of a colloidal nature.
SEPARATION OF CACCIUM AND MAGNES!U1!
As mentioned before, the dense sheets of caliche usually have a ~ow
percentage of magnesium carbonate, while the soil ahoye and helow
these strata may run relatively high in magnesium. In pure water,
'calcium carbonate is sohtble abont 10 parts per million, while magnesium
carbonate is practically insoluble. A~ both salt~ are relatively insoluble,
<16
EXPERHIESr sT.HID'\" BC'LLBTIS So.
I.?!
a separation of them as carbonatel> is difficult. They occur combined ill
nature, as dolomite which is exceedingly insoluble.
In the presence of carbon dioxide, however, calcium carbonate is
soluble to the extent of l,OOCJ parb per million a~ calcium bic:.trhonate,
willIe the solubility of magnesium bicarbonate, under the same condition, may nUl a~ high as 12,CXXl parts per million. This wide difference
III the solubility of the bicarhonate;, probably i~ in nature the principal
means of the separation of the two salt~. In a precipitation caused by
the total evaporation of the watt'r, all the calcium and all the magnesium
would be precipitated, and remain in,>oluhle as caliche. This would represent conditions in a "oil. where compkte evaporation was taking place
and where no leaching wa~ going on. If a partial precipitation took
place from a solution. a~ might happen in shallow pools upon the .,urface
which were subject to occa!>ional overflow. the calcium carbonate might
be precipitated in greater proportion than the maglle~itl1u, and the magnesium bicarbonate might be carried off to the ~ea. The small amount
of magnesium carbonate il1 the dense. sheet~ of caliche indicate partial,
rather than complete precipitation.
Another property of calciwll which distlllg1tl~hes it from magnesium,
IS the tendency of calcium carbonate to precipitate around solic! particles
of other material, and to form a cement, or concrete. Magne<.lum docs
not pO'isess thi~ property to any great degree. in fact. the presence of
magnesium in cement i~ very objectionable. as it interferes seriotl~ly
with the "setting" of the concrete. If, therefore. a mixtttre of a solution
of calcium bicarbonate and magnesium bicarbonate is evaporated partially in the presen~e of sand and gravel. the calcium carbonate will tend
to crystallize more readily than the maglle<;itlln. Tn the natural formation of caliche, calcium carhonate wonld remain in the ~I)il, while the
magnesium would be carried off toward the l'ea.
As mentioned before. ll('arly all ground and flood \\'atcr~ in Arizona
contain calcium l'ulphate. a'> well as calcium bicarbonate. ""hen no
evaporation takes pJace. but wht'l1 there is a relief of pre~l'ttre. carhon
dioxide escapes. and calcium carbonate jl' precipitated. The los,> in
carbon dioxide has little or no effect upon the l'olubility of calcium sulphate. which remains in solutioll. Tn thi~ way a ~eparation of calcium
carbonate and calcium sulphate is made.
PEBIllJ£S UPON THE SURF.\(,E OF C.\T .. ICrIE
When caliche occurs as a conglomerate, the pebbles which it contains
are usually water worn. Some of the pebbles, hy their state of erosion,
mdicate that they have bern transported long distances. while others are
more angular, and probably have not been moved very far from the
CA.LIClm I.\, ARIZO.VA
437
original rock. In thousands of cases a condition like that shown in
figure 6 is seen.
The caliche occurs in a succession of dem.e sheets at all depths in the
soil, as has ileen descrihed already, while over the upper sheet, which is
usually fairly pure calcium carbonate, many pebbles are scattered. The
stratification of the caliche runs unbroken beneath these pebbles as is
"hown in the figure, but the pebbles are attached to the top of the caliche
by a thin layer of calcium carbonate. The pehhles are covered with very
thin, laminated layers of calcium carbonate.
Fig. 6.-1J1ustration showing a pi~e of cahche stratum with
the snrface. Natural sire.
pebhle~
cemented upon
Such a phenomenon may bl:" explained in more than one way, It IS
true, but when combined with other evidence, it indicates that the caliche
stratum was formed .upon the surface, and that afterward the pebbles
were washed in and became attached to the top sheet. If the pebbles had
been in plac(' during the fonnation of the caliche, that is if the caliche
had been fomlcd below the surface of the soil by the evaporation of
either descending or ascending water, the pebbles would probably have
been included in the ~tratification. The laminated layer" around the
pebbles consi"t of v('ry pure r-akium carhon;]te.
CALICHE I'ROB.\BT.Y F('RMED IN LAKES OR POOLS
The valley fill in many of the drainage hasins in Arizona is very thick.
The depth to bed rock in the Santa Cntz basin near Tucson, for example, has not heen determined accurately, but it is at least 2,000 feet.
The fill is equally as deep in the San Simon and in other valleys. This
depth of debris in the Santa Cruz Valley represents largely the products
of erosion from the Catalina. Rincon, and Santa Rita mountains. This
438
EXPERIMENT ST,lTIO}: BULLETIN .Vo. IF
valley fill is all stratified, and the pebbles and rock fragments are nearly
all water worn. Unquestionably the fill was laid down by the streams
which came down from the mountains on either side of the valley Or by
the rivers which came from the south and southeast, causing the fill
material to migrate laterally. Deposition ceased many cehturies ago,
and erosion is now taking place, so thE' floor of the valley today is probably much lower than it was when its highest point represented the
flood plain of the Santa Cntz River.
During the long period which was required to build up the 2.000 feet
or more, there was at time~ an abundance of water in the valley, and
the entire surface was subjected to overflow. The soil in this valley is
usually dispersed, that is, it puddles easily, and does not take water
readily. If an area is leached with pure water, the water will, at first,
percolate the soil but, if the leaching is continued, the soil soon becomes
Impermeable, and water will stand upon the surface until it evaporates.
During past ages, conditions were probably ideal for the formation of
small, shallow pools, or playas, where W:lter stood for a long period of
time. These playas may have been only a few yards in diameter, or
they may have covered se-veral acres. They were subjected to occasional
overflow, and their contours were being changed continually by deposition of sediment from such overflows. During this time, evaporation
must have been very great, and it must have required large amounts of
water in order to maintain a marshy condition over any great area.
The stagnant water must have furni~hed an excellent place for the
growth of algae, marsh grasses and such vegetation.
If the flood water which filled these playa~ contained calcium bicarbonate in solution. and if such water was evaporated, a deposit of calcium
carbonate, or caliche, would have been made.
A few miles southwest of Tempe, in the Salt River Valley, S. E.
corner Section 20. Township 1 N., Range 4 E., a typical playa of fairly
recent origin may be seen. This playa covers over 40 acres and was
covered originally with coarse ve-getation. A part of it has been reclaimer! and is now planted to ('otton. The soil in thi~ playa is very
heavy, and the entire area is unde-flain by a thick ~tratum of very dense
caliche.
The first reqlti~jte for the formation of a playa is that a barrier must
be fonned which preYents a part, if not all, of the Rood water from
running off. The second re'1uisite is an imperme-able subsoil which prevents drainage. Under such conditions, as shown in the Tempe area,
flood water will collect and stagnate, until it deposits its load of calcium
carbonate, and is removed by evaporation.
Such a condition as that represented in this playa, might have been
common during the ages when the valleys of Arizona were being filled.
CALICHE
n-
ARIZO,V.-J.
"'9
It is not nece<;sary to assume that the Santa Cruz Valley, for example,
was ever a great inlancl lake, or that the playas were very large. The
structure of the caliche indicates that it was formed usually in very small
pools.
Ill] U! ;:}lP![UJ }O ElU.q~ U!lJlUOJ Ol llY: ,{~Ut:A ;;)ql pddxd prnoqs d Y\
horizons, provided the flood water at all times contained calcium bicarbonate. A deep well wa~ dug recently about 3 miles east of Tucson,
and the log of this "'ell showed a <;tratU11l of caliche, about 3 feet
thick, beneath about 6 inches of soil. Deeper drilling showed a succession of sand and gravel strata, until a level of 71 feet was reached.
Here another stratum of caliche, several feet thick, was encountered.
·Water was found at lli feet, but the well was drilled to a depth of 351
feet. Cemented .,and. probably soft caliche. was reported at depths of
130,235,250, 2iS, "OR, 32R, and 3::'1 feet, respecti\·clv.
Another well, 2,000 fect deep, \Va" drilled recently in the San Simon
Valley. and the entire core was found to be calcareous. Distinct strata
of cemented "and and clay were found at many depths.
The chemical compo'lition of flood waters depends upon the nature
of the sailor rocks in the water shed. If, during one era, great deposits
of gypSUlll were exposed hy erosion and were subject to leaching, the
flood waters would be high in calcium sulphate. If erosion exhausted
these beds of gypsum. and depo~its of limestone were exposed. the flood
water could change in composition and hecome highly charged with
calcium bicarbonate. vVe know that such changes have taken place
during the period when these valleys were being filled. We should not,
therefore, expect strata of caliche to be formed in the valleys except
during the eras when the flood waters contained sufficient amounts of
calcium hicarbonate.
C'LICHE OF ORGANIC ORIGIN
Dr. A. E. Vin<;oll (G), exprcs."e~ the opinion that lime-secreting
organisms were re5pon'lible for the formation of the caliche around
Tucson. He points out that, ,)ver mn.lly depo!:-its of caliche there is a
pure stratum, or cap, and that the strongest evidence of organic origin
is found in the:;e caps. It i.. well known that the soil under leaky
hydrants in Tucson develops a growth of green algae, and that these
algae soon produce a calcareous crust which resembles caliche. Vinson
is of the opinion that caliche was formed upon the surface and not in the
subsoil, and that it was laid down either in water, or upon soil that was
wetted frequently with limy water. During the intervals that were
comparatively quiet, in the periods of deposition, little debris was introduced, and the caliche cap was built up quite pure. During period., of
EXPERIMENT 'lTATION BULlJl.Tl\' .10,'0.
]~]
floods, however, sand, gravel, and other debris were deposited upon
the caliche, which checked the growth of the organisms, and, mixing
with the caliche which was afterwards fonned caused the seams of loam
and loose cemented caliche, which lie between the denser strata.
It has been observed by W. T. McGeorge, of this laboratory, that
many ground waters will become alkaline enough to react with phe~
nolphthalein, when a growth of green algae appears in the solutions.
'rhis phenomenon i.<, true with algae which are not lime secreting.
Apparently, algae, when grown in a solution of calcium bicarbonate,
will absorb the carbon dioxide and the calcium carbonate will be pre~
cipitated.
If the dense strata of caliche were deposited in stagnatlt water, the
deposition may have been ~timulated greatly by the presence of algae.
CONCLUSIONS
1.
,
3.
4.
5.
6.
Caliche, wherever found in Arizona, was formed by the solution,
transportation, and precipitation of calcium c.,rbonate.
'Alater, when charged with carbon dioxide, di~solves calcium carbol1~
ate and forms calcium bicarhonate. The cnlciu111 bicarbonate i~
carried in solution cmd i" precipitated as c:tlcium carbonate, or
caliche, when the water is evaporated, or when there i~ a relief in
pressure, which drives off carbon dioxide,
Caliche strata may be formed beneath the surface of a fioil, either
by the evaporation of descending surface water, or by the evaporation of ascending grol1nd "at('r.
Caliche may be formed in a soil by means of plant roots. Plants
growing upon the surface absorh s0il water for transpiration purposes, and the calcIum carbonate that is dissolved ill the soil solu~
tion is precipitated as caliche.
As long as they are pennt"able to ·water, caliche strata will move
downward in a soil as fa~t as erosion removes the upper soil surface.
Caliche probably is formed upon the surface of a soil by the evapora~
tion of surface or flood water. The formatiOll under such condi~
tions is hastened by the presence of algae and other water plants.
CAUClllj IX .lR1ZONA
441
BIBLIOGRAPHY
L
make, W. P.-The Caliche of Southern Arizona, Am. Inst. Mng.
Eng. vol. XXXI, pp. 220-220.
2.
Forbes, R. H.-Ariz. Agr. Exp. Sta. Bull. 28, p. 90.
3.
Guild, F. N.-Mineralogy of Arizona, 1910.
+.
Lee, \V. T.-Underground waters of the Salt River VaUey, Arizona,
U. S. Geol. Surv. Water Supply Papers, No. 136, 1905.
:1.
Tolman, C. F., Jr.-The Geology of the vicinity of the Twnamoc
Hills, Publication 113, Carnegie Institute of Washington, 1908.
6.
Vinson, A. E.-Twenty-sevellth All1lt1.a.l Report, University of
Arizona, Agricultural Experiment Station, 1916, p. 298.
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