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~ GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1647-A 

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WISCONSIN GEOlOGICAl :SURVEl' 

Geology and Ground-Water 

Conditions in the Gila Bend 

Indian Reservation 

Maricopa County, Arizona 

By L. A. HEINDL and C. A. ARMSTRONG 

WATER SUPPLY OF INDIAN RESERVATIONS-PAPAGO TRIBE 

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1647-A 

Prepared in cooperation with the 

Bureau of Indian Affairs 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1963 
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary 

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director 

For sale by the Superintendent of Documents, U.S. Government Prlntinl!, Office 

Washlnl!,ton 25, D.C. 
CONTENTS 

Page 

Abstract__________________________________________________________ Al 

Introduction______________________________________________________ 2 

Previous investigations_____________________________________________ 4 

GeologY---------------------------------------------------------- 6 

Rocks and their water-bearing properties_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 7 

Crystalline rocks__________________________________________ 7 

Sil Murk formation________________________________________ 10 

Sedimentary member__________________________________ 11 

Volcanic member______________________________________ 15 

Correlation, age, and origin_____________________________ 19 

Tertiary and Quaternary alluvial deposits____________________ 21 

Older alluvial filL_____________________________________ 22 

Younger alluvial fill____________________________________ 23 

Subsurface stratigraphy__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 23 

' Structure_____________________________________________________ 27 

Geologio history__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 29 

Water resources_----- _________ ,____________________________________ 31 

Surfacewater_________________________________________________ 32 

Groundwater_________________________________________________ 33 

Valleyfill_________________________________________________ 33 

Occurrence of ground water and slope of the water table____ 33 

Recharge_____________________________________________ 36 

Discharge____________________________________________ 36 

Storage_______________________________________________ 36 

Fluctuations__________________________________________ 38 

Quality of water_______________________________________________ 40 

Availability of ground water for future development__ _ _ _ _ _ _ _ _ _ _ _ _ _ 42 

Summary and conclusions___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 44 

References cited__ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 45 

Index____________________________________________________________ 47 

III 
FIGURE.L .Index map of .. G~Ia Bend, Papagq, . . . Reservations ___ ~ ___ ~ ___ ~.:.~ __ ~--._ __ -~·~;.; ______ .. ___ --~ __ 

2. Inde:X: map of Gila plain and adjacent mountains .... ~-~-

3. View of Gila Bend Moun1~airts_.:. 

4. Geologic map showing of 

5. Topographic relationships of the Sil Murk xurwablUil• 

6. Thin-bedded red arkosic sandstone that forms the 

exposed part of the Sil Murk formation---------------.---

7. Lower part of well-indurated fanglomerate of the Sil l\-furk formation _____________________ .. ____ .. ____ .. ___ .. ____ ~ ___ ~ 

8. Weakly consolidated fanglomerate of the Sil Murk formation __ 

9. Interbedded fanglomerate and gray conglomerate of the Sil 

Murk formation _____________________ ------_----------"" . 

10. Diagrammatic section showing angular unconformity between 

fanglomerate and volcanic members of the Sil Murk formation-------------------------------------------------~ 

11. Contact between tuffaceous sandstone and ash bed of the 

volcanic member ______________________________ ----- __ _ 

12. Dacitic welded tuff of the volcanic member ________________ _ 

13. Generalized block diagram of Gila Bend Mountains a~d Gill!> 

Bend plain ________ ----------.. -----"-----'"---.. .,. .. ------- 14. Annual ground-water pumpage and water-table fluctuations.;;~ . 

TABLES 

TABLE 1. Drillers' logs of selected wells in the vicinity of the Gila Bend . · Indian Reservation ________ .. ___ ...... _ .... __ .......... ~-----_-~-~_ 

2. Description of selected wells in the Gila Bend Indian. Reservation 

and vicinity ___________________ .. -----.-------------· .. --.-

3. Chemical analyses of water from selected wells in the vicinity 

of the Gila Bend Indian Reservation------------·----"~~~-
WATER SUPPLY OF INDIAN RESERVAT ONS-PAPAGO TRIBE 

GEOLOGY AND GROUND-WAT R CONDITIONS 

IN THE GILA BEND INDIAN ESERVATION, 

MARICOPA COUNTY, RIZONA 

I 

I 

By L.A. HEINDL and c. A. rSTRONG 

ABSTRACT I 

The Gila Bend Indian Reservation, Maricopa;County, Ariz., comprises an 

area of 16 square miles about 3 miles north of Gil Bend, Ariz. The Gila River 

flows across the reservation at an altitude of abo t 620 feet, and the Gila Bend 

Mountains, which form the northwestern partt of the reservation, rise to 

an altitude of about 2,000 feet. · 

The reservation is underlain by crystalline rock~ of possible Precambrian and 

Mesozoic ages, red sandstone, fanglomerate, collltlomerate, and volcanic rocks 

of probable Tertiary age, an older alluvial fill of tt'ertiary and Quaternary age, 

and channel and flood-plain deposits of Quaternao/ age. The Gila Bend Mountains are composed of granitic, metamorphic, and I volcanic rocks, and older terrestrial deposits and appear to be a fault block th~t has been tilted to the west. 

The older alluvium and the channel and flood-plain !deposits were laid down on an 

eroded surface of the tilted block. The fiood-pl*n deposits are about 80 feet 

thick and are underlain by older alluvium, whicl in this area is about 300 to 

500 feet thick. The sandstone, fanglomerate, andt volcanic rocks are more than 

1,500 feet thick. · 

The principal aquifer is in the valley fill, which !comprises hydraulically interconnected parts of the older and younger alluvi~l deposits and the sandstone, 

fanglomerate, and conglomerate of Tertiary age. i This aquifer yields water in 

large quantities. The crystalline rocks are virtlially not water-bearing. The 

principal recharge to the alluvial deposits is byin!filtration from the Gila River. 

Large quantities of water are in storage in these de~osits. 

The concentration of dissolved solids of most pf the ground water obtained 

from the valley fill ranges from about 1,000 to 3~500 ppm. The water is high 

in sodium, chloride, boron, and fiuorid~. The sutface water of the Gila River 

during periods of low flow contains more than 5,poo ppm of dissolved solids--

chiefly sodium, calcium, magnesium, and chloride. t, Painted Rock Dam, now being constructed acr s the Gila River for floodcontrol purposes about 11 miles downstream fro the reservation, will have a 

spillway at an altitude of 660 feet. When the Iieservoir behind the dam fills 

to the level of the spillway, all the reservation, tcept for the part in the Gila 

Bend Mountains, will be inundated. However, 1 ng-term effects of inundation 

by high water likely will be unimportant beca se the reservoir will receive . 

water only from infrequent maximum floods, and ,the water will not be retained 

permanently in the reservoir. 1 

Al 
A2 WATER SUPPLY OF INDIAN RESERVATIONS-PAPAGO TRIBE 

INTRODUCTION 

The study of ground-water resources of the Gila Bend Indian Reservation is part of an investigation of the ground water available to 

the Papago Indian Tribe. The study was made by the Geological 

Survey in cooperation with the Bureau of Indian Affairs. The Bureau 

of Indian Affairs requested data regarding the possibilities of developing water supplies for bot~1 range and irrigation purposes, and an 

opinion regarding the possible effects of Painted Rock Dam being 

constructed about 10 miles downstream and west of the reservation 

(fig.l). 

;;: ~-{~~#l#tttt~~~A@N lER lt="N:::;Dl;::AN'-j-----· RESERVATION 

-........._ Nogal~ _ 111 0 110° 109 

50 50 tOO Miles 

FIGURE 1..---.lndex map of Arizona showing Gila Bend, Papago, and San 

Xavier Indian Reservations. 
GROUND WATER, GILA BEND INDIAN RESERVATION A3 

The Gila Bend Indian Reservation, the smallest of three Papago 

Indian Reservations, is 16 square mij es in area, and is in the Sonoran 

Desert section of the Basin and Range province (Fenneman, 1931) . 

It is 3 miles north of Gila Bend, Ariz., at the north end of a large 

gently northward-sloping intermontane basin called the Gila Bend 

plain, and at the south end of the Gila Bend Mountains (fig. 2) . Immediately east of the Gila Bend Indian Reservation the Gila River 

bends from south to west to give the region its name. The reservation is divided by the Gila River, which here marks the boundary 

between the Gila Bend plain and the Gila Bend Mountains. 

E XPL A NATI ON R . 5W. 

CJ 

Bedrock 

r. 

Older Gila River flood plain 

PAINTED 

ROCK 

R.7W. 

DAMSITE ~ _ _. 

-...*- <>' \.. ,./ 

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CJ Surface deposits on Gila Ben<! ~~~neeplain except for inner flood 

plain and cha nnels of Gila Ri ver, whi ch are separately marked 

Outline of area mapped 

in this report 

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P l A I N 

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FIGURE 2.-Index map of Gila Bend pl•a ln and a djacent mountains, Rhowing outline of 

hard-rock outcrops. After Babcock and others (1948, pl.. 1) . 
A4 WATER SUPPLY OF INDIAN RESER'VATIONIS--PAPAGO TRIBE 

The altitude of the Gila River at the southernmost tip of the Gila 

Bend Mountains is 620 feet, and the Gila Bend Mountains rise to an 

altitude of about 2,000 feet. The area is drained by the Gila River, 

whose gradient here is about 6 feet per mile and whose flood plain 

is 2 to 3 miles wide. About 10 square miles of the reservation consists of the channel and flood plain of the Gila River and low terraces 

of the Gila Bend plain. The rest is in the foothills and more rugged 

areas of the Gila Bend Mountains. 

In 1955 about 375 acres of arable land was under lease to non-Indian 

personnel. Commercial crops of cotton, barley, alfalfa, and sorghum 

were grown on this land. In addition, about 1,200 acres are considered by the Bureau of Indian Affairs to be arable and a few head 

of cattle graze within the reservation. About 130 Papagos were permanent residents of the reservation in 1958 according to G. W. Gilmore, Papago Indian Agency superintendent (written communication, June 23, 1958). Sil Murk is the only Papago village in the 

area, but it is not on the reservation. 

The climate of the area is arid, and is characterized by hot summers and mild winters. A climatological station was established at 

Gila Bend in 1903 and is still in operation, although records from 

the station have not been continuous. Data from the station at Gila 

Bend indicate that precipitation averaged about 5.5 inches per year 

for 52 years of record, ranging from a minimum of 2.13 inches to a 

maximum of 13.58 inches. The mean annual temperature for 32 

years of record is about 72°F, ranging from a maximum summer 

temperature of 123°F to a minimum winter temperature of 11 °F. 

Potential evaporative losses were estimated to be about 96 inches per 

year in the Gila Bend area (Johnson and Cahill, 1955, p. 18). The 

frost-free season averages about 9% months per year. 

The geology of the reservation was mapped and hydrologic data 

from the immediately adjacent areas were examined and brought up to 

date in early 1957. The fieldwork was begun by C. A. Armstrong in 

1954 and completed by L.A. Heindl in 1960. 

PREVIOUS INVESTIGATIONS 

The geology and ground-water resources of the Gila Bend region 

have been discussed by several writers whose reports, listed chronologically below, have provided the regional data necessary to analyze 

the local conditions of the Gila Bend India.n Reservation. 

1914. Phalen, W. C., Celestite deposits in California and Arizona: U.S. Geol. 

Bull. 540-T, p. 521-533. 

Briefly describes a tilted sedimentary series associated with gypsum, 

sandstone, conglomerate containing pebbles of coarse-grained granite, 
GROUND WATER, GILA BEND INDIAN RESERVATION A5 

and basaltic :flows in the north end of the Sauceda Mountains, about 

15 miles south of Gila Bend. 

1922. Ross, C. P., Routes to desert watering places in the lower Gila region, 

Arizona: U.S. Geol. Survey Water-Supply Paper 490-C, p. 271--315. 

Describes \vatering points along roads west of Gila Bend. 

1922. Bryan, Kirk, Routes to desert watering places in the Papago country, 

Arizona: U.S. Geol. Survey Water-Supply Paper 490-D, p. 317-429. 

Describes wate1ing points along roads south and east of Gila Bend. 

1922. Ross, C. P., Geology of the lower Gila region, Arizona: U.S. Geol. Survey Prof. Paper 129-H, p. 183-197. 

First description of some geologic features in the Gila Bend area; 

discusses crystalline rocks of two ages and Tertiary and Quaternary 

sedimentary and volcanic rocks, general structural relationships, history and some mineral deposits; includes first generalized geologic map 

of the area. 

1923. Ross, C. P., The lower Gila region, Arizona, a geographic, geologic, and 

hydrologic reconnaissance with a guide to desert watering places : 

U.S. Geol. Survey Water-Supply Paper 498, 237 p. 

Includes resume of geologic data in Professional Paper 129-H, 

ground-water data in the Gila Bend area, description and physiographic 

history of the lower Gila River, and history of irrigation development. 

1925. Bryan, Kirk, The Papago country, Arizona, a geographic, geologic, and 

hydrologic reconnaissance with a guide to desert watering places: 

U.S. Geol. Survey Water-Supply Paper 499, 436 p. 

General description of physiography and ground-water conditions of 

Gila Bend plain. 

1925. Darton, N. H., A resume of Arizona geology: Arizona Bur. Mines Bull. 

119, p. 226-227. 

Briefly mentions major features of the Gila Bend Mountains. 

1933. Wilson, E. D., Geo·logy and mineral deposits of southern Yuma County, 

Arizona: Arizona Bur. Mines Bull. 134, p.144-147. 

Briefly describes the Gila Bend Mountains and some gold and copper 

mineralization. 

1948. Babcock, H. M., and Kendall, K. K., Geology and groundwater resources 

of the Gila Bend basin, Maricopa County, Arizona, with a section on 

Quality of water by J. D. Hem: U.S. Geol. Survey open-file rept. 

Brief, comprehensive summary of the geology of the area with first 

detailed discussions of ground-water conditions and chemical quality of 

surface and ground water; includes tables of well records, logs, and water 

analyses, and a generalized geologic map. 

1952. Coates, D. R., Gila Bend basin, Maricopa County, Arizona, in Halpenny, 

L. C., and others, Ground water in the Gila River basin and adjacent 

areas, Arizona-a summary: U.S. Geol. Survey open-file rept., p. 159-

164. 

Summarizes the report by Babcock, Kendall, and Hem (1948), supplemented by later pumpage and water-level data. 

1955. Johnson, P. W., and Cahill, J. M., Ground-water resources and geology of 

the Gila Bend and Dendora area, Maricopa County, Arizona: U.S. 

Geol. Survey open-file rept., 53 p. 

Describes the geology and hydrology of the area between Gillespie 

Dam and a point about 10 miles downstream from the Painted Rock 

damsite; brings up to date information on water resources and de649978 Q-62--2 
A6 WAT.ER SUPPLY OF INDIAN RE.SERVATIONlS-PAPAGO TRIBE 

scribes evapotranspirative r egimen of river-bottom vegetation in the 

area; includes maps of geology, water tables, and dissolved-solids content, tables of ground-water use by bottom-land vegetation, records of 

selected wells, well logs· and chemical analyses of water, and charts 

showing water-table fluctuations and other hydrologic relationships. 

GEOLOGY 

The Gila Bend Indian Reservation includes three principal topographic features-the Gila Bend Mountains, the flood plain of the 

Gila River, and the broad terrace of the Gila Bend plain (fig. 3) . 

These features are expressions of the principal geologic units discussed in this report and shown in figure 4. The Gila Bend Mountains trend north-south and are the exposed part of a tilted fault 

block. They are composed of granite and associated igneous and 

metamorphic rocks and arkosic sandstone, fanglomerate, and volcanic 

deposits. The flood plain of the Gila River and the broad terrace of 

the Gila Bend plain south of the reservation are underlain by poorly 

consolidated alluvial materials. 

FIGURE 3.-General view of the eastern part of the Gila B;end Mountains looking north. 

Main ridge is com,posed of cr·y&talllne rocks; ridge Including hill 1106 is composed of 

gray boulder conglomerate and t he dark cuesta In left middle ground Is composed of 

volcanic rocks of the Sil Mu rk formation. The sharp bend of the Gila River, which gives 

the Gila Bend a r·ea its place names, occurs immediately to the righ t of the photograph; 

in the u,pper right, the dark area in t he valley between the Gila Bend and more distant 

Maricopa Mountains marks part of the north-south leg of the bend·; the dark urea in the 

middle ground Is the heavily v!'getnted• land a long the channel of the east-west leg of 

the bend. The large light area in the middle ground is cultivntecl land in the flood 

plain of the Gila River and the dissected area in the foreground Is cut into older alluvial 

fill . 

Several deep water wells in the area adjacent to the reservation 

provide data for speculation regarding the stratigraphy underlying 

the Gila Bend plain, and these data are discussed in the section "Subsurface stratigraphy." 

No definitely dated late Precambrian, P aleozoic, or Mesozoic 

sedimentary rocks are exposed in the Gila Bend Mountains. The 
GROUND WATER, GILA BEND INDIAN RESERVATION A7 

1,500-foot thickness of late Precambrian rocks in the mountains 45 

miles southeast of the area (McClymonds, 1959) suggests that rocks of 

the same age may have extended at one time as far west as the Gila 

Bend Mountains. Remnants of moderately thick sections of Paleozoic 

and possibly Mesozoic sedimentary rocks are exposed at a few places in 

the region (Wilson · and others, 1957, 1959; McClymonds, 1959). 

Tertiary ( ~) conglo!llerate containing large boulders of Paleozoic lime~ 

stone has been reported in nea,rby mountains (Wilson, 1933 ; McKee, 

1947); these boulders suggest that the area was at one time covered 

by Paleozoic and possibly some Mesozoic sedimentary ·strata. Thick 

sequences of volcanic rocks, in part older than the Sil Murk formation, 

crop out extensively in the northern part of the Gila Bend Mountains 

and other nearby ranges (Wilson and others, 1957). 

ROCXS AND THEIR WATER-BEARING PROPERTIES 

CBYSTAL1JNEBOCKS 

The main ridge of the Gila Bend Mountains is composed of metamorphic and igneous rocks, which will be referred to collectively as 

crystalline rocks. The ridge rises to a sharp lineral crest whose flanks 

are scoured by a close succession of steep, narrow ravines. The oldest 

rocks in the Gila Bend Mountains are gneiss and schist, which are 

tentatively correlated with the Cardiga,n gneiss of presumed Precambrian age in the Ajo area (Babcock and others, 1948, p. 6). The 

gneiss and schist occur only locally and are predominantly brownish 

gray and prominently banded or foliated. Much of the gneiss is 

closely jointed. The gneiss is-generally more resistant to erosion than 

the schist and forms the bolder outcrops. 

The early Precambrian ( ~) gneiss and schist are intruded by finely 

to coarsely crystalline equigranular to porphyritic granite that forms 

most of the Gila Bend Mountains. Wherever observed, the granite 

is gneissoid. The granite is generally light gray and weathers 

brownish or greenish gray. It contains numerous inclusions and locally these string out from bodies of older schist. The granite is well 

jointed to massive and weathers to well-rounded large fragments and 

whole or broken mineral crystals. The granitic rocks are correlated 

tentatively with the Chico Shunie quartz monzonite of presumed 

.Mesozoic age in the Ajo quadrangle by Babcock and others (1948, 

p. 7), but Wilson and others (1957) consider the granite to be Precambrian. The gneiss, schist, and granite are intricately crisscrossed 

by numerous mafic, felsic, and pegmatitic dikes. 

The crystalline rocks are all extensively sheared and fractured and 

may contain small amounts of shallow "surface" ground water, but 

none has been developed in this area. 
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Base from U. S Geological Survey topographic maps 

Wool sey Peak , 1951; Theba, 1951 ; Gila Bend , 1951; 

Cotton Center, 1951 0 

CONTOUR INTERVAL 20 AND 40 FEET 

DATUM IS MEAN SEA LEVEL 

2 MILES 

Geology by C. A. Armstrong, 1954 

and L. A. Heindl, 1956 

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nger alluvial fill 

Qal, nearly unconsolidated gravel, sarul, silt, and clay; 

olde,·fiood-plain deposits; Qc, Gila River channel 

and younger }lood-plain depos-its; yield water in 

large quantities to iniyation wells; may include 

small anas oj' QTal. 

/).;i~H\// I Older alluvial fill 

Poorly consolidated conglomerate, sandstone, and 

m1<dstone; sU?face deposits include fan, sheet wash, 

and ten·ace deposits; yields wateT in large quantities /.o i1'1'igation wells; includes small areas of 

Qal and channel deposits 

UNCONFORMITY 

Sil 

-

Murk formation 

Tsm, moderately to poo1'ly consolidated sandstone, 

fanglomerate, and conylornera/.e; Tsv, volcanic member and inte1·calated conglornemte. Tsm 

yields water in rnodemte quantities to irrigation wells; Tsv may yield small quantities of water from 

fractured zones or conglome1·ate lenses 

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UNCONFORMITY 

Crystalline rocks 

CAmplex of intrusive and metamorphic rocks; 

bear little or no water in the area 

Gontact, approximately located 

··?······~·······?·· . D . 

Probable buried fault 

U, upthmwn side; D, d01!Jnthrown side 

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Strike and dip of beds 

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Domestic or stock well 

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Irrigation well 

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Abandoned well 

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Sections along line A-A' found on 

figures 10 and 13 

F IGU RE 4.-Geologlc map sh owing location of wells in the Gila Bend India n Reser vation and immediately adjacent areas. 
AlQ WATER SUBPLY OF INDIAN RE.SERVATION1S-PAPAGO TRIBE 

SIL MURK FORMATION 

Extensive exposures of conglomerate, fanglomerate, sandstone, and 

volcanic rocks crop out in the southwestern part of the Gila Bend 

Mountains (fig. 4). They are also presumed to underlie the Gila 

Bend plain immediately to the south of the Gila Bend Mountains. 

These rocks are here named the Sil Murk formation for their excellent exposures 2 to 4 miles northwest of the village of Sil Murk. 

The topography developed on the Sil Murk formation depends on 

the predominant rock type involved. The sandstone and fanglomerate are less resistant to erosion than the conglomerate and volcanic 

deposits and typically underlie valleys or form slopes (fig. 5) ; the 

conglomerate is moderately resistant and forms a prominent ridge 

FIGURE 5.-View northwest from the center of sec. 2, T. 5 S., 

R. 1l W., to hill 11()6 in the NW~ sec. 3, showing topo· 

graphic relationships of the Sil Murk formation . Fore· 

ground is composed of red arkosic sandstone, a nd hill 1106 

is composed of gray boulder conglomerate. Covered area in 

the center of photograph Is unde rlain by fanglomerate tha t 

is transitional between these two J'acles. 
GROUND WATER, GILA BEND INDIAN RE:SERVATION All 

of rounded hills in the area; and the volcanic rocks, particularly the 

welded tuff, are the most resistant, forming conspicuous cuestas and 

low hills. 

The Sil Murk formation in the area is composed of a sedimentary 

member overlain by a volcanic member. The sedimentary member 

is composed of two facies. The lower facies is predominantly a brickred, thinly bedded, arkosic sandstone. This facies grades upward 

through· a zone of moderately indurated fanglomerate, composed of 

interbedded pebbly sandstone and sandy conglomerate, into the upper 

facies, a gray boulder conglomerate which forms the ridge described 

above. At the top of the Sil Murk formation at the south end of the 

Gila Bend Mountains is a volcanic member composed of tuffs, flows, 

and intercalated conglomerate lenses. 

The base and top of the Sil Murk formation are not exposed in the 

area but they are exposed in the Gila Bend Mountains about 6 to 10 

miles north of Sil Murk. There the lower sandstone facies is locally 

absent; the volcanic member is intercalated between clastic deposits; 

and the top of the formation is a conglomerate similar to the gray 

boulder conglomerate exposed at the south end of the Gila Bend 

Mountains. 

SEDlMENTARY MEMBER 

The lower sandstone facies is best exposed in the narrow valley 

between the crystalline rocks and the prominent ridge to the west 

(fig. 4) . Several small exposures are shown as a single outcrop on 

figure 4. The sandstone forms some low hillocks and bare rocky 

spots, inconspicuous except for their color, but is exposed best along 

the banks of some of the deeper washes. The brick-red sandstone is 

medium to coarse grained, arkosic, and contains differing but conspicuous amounts of magnetite and, less commonly, biotite. Quartz 

grains are angular to subrounded. The sandstone is weakly consolidated with lime. Bedding is well developed and -the beds range 

in thickness from less than a quarter of an inch to about 12 inches 

(fig. 6). Pebbly and cobbly beds increase in proportion to sandy 

beds upward in the section. The larger fragments are composed 

entirely of crystalline rocks exposed in the main ridge of the Gila 

Bend Mountains (fig. 7). About 100 feet of sandstone is exposed in 

the area, but the total thickness is not exposed and may be as much 

as several hundred feet. 

The contact between the sandstone. facies and the crystalline rocks 

to the east is covered by alluvial material disgorged from the adjacent 

canyons of the Gila Bend Mountains. The contact is presumed to be 

depositional for lack of contradictory evidence and is so described 

by Babcock and others ( 1948, p. 4) in surrounding areas. 
A12 WATER SUPPLY OF INDIAN RE:SERVATIONIS-PAPAGO TRIBE 

FIGURE 6.-Thln-bedded red arkosic sandstone that forms the lowest exposed part of the 

Si!!lfurk formation In the center o~ sec. 2, T. 5 S., R 5• W. 

FIGURE 7 .. -Lower part of well-indurated fanglomerate of the SH l\furk formation In the 

center of sec. 2, T. 5 S., R. 5 W.. The fanglomerate Is compo&'(ld of Interbedded red 

arkosic snndstone a nd cobbly beds. 
GROUND WATER, GILA BEND INDIAN RESERVATION A13 

The fanglomerate forms a transitional zone between the sandstone 

and gray conglomerate, and is well exposed in the NWJ.M sec. 2, T. 

5 S., R. 5 W. in the main southwestward-trending wash coming out 

of the Gila Bend Mountains and the large northward-trending wash 

between the mountains and the gray conglomerate ridge (figs. 8 and 

9). The fanglomerate is composed of interbedded light-reddishbrown pebbly sandstone and cobbly conglomerate. Generally it is 

better indurated than either the underlying sandstone or the overlying 

conglomerate. Ross (1922, p. 196 and pl. 44) reports an angular 

unconformity between the red sandstone and an overlying conglomerate, which he correlates with the gray conglomerate facies in the vicinity of Woolsey Tank (Ross, 1923, pl. 4) about 20 miles northwest 

of Sil Murk. However, the conglomerate above the unconformity in 

that area is a younger deposit that resembles the gray conglomerate 

only because it is locally well indurated by caliche .. 

The gray conglomerate facies of the lower member of the Sil Murk 

formation is composed of poorly sorted beds of boulder to pebble 

conglomerate, sandstone, and mudstone. There is a general decrease 

in the size of the fragments from the eastern to the western part of the 

area. The boulder beds are thick, lenticular, and poorly and irregularly developed. The pebbly sandstone and mudstone are more distinctly and thinly bedded and many of the sandstone beds are 

erossbedded. Generally the gray conglomerate is moderately conFIGURE 8.-Weakly consolidated fanglomerate underlying poorly consolidated gray conglomerate of the S.il Murk formation in the NW'4 sec. 2, T. 5 S., R. 5 W. 

649978 0-62- 3 
A14 WATE'R SUPPLY OF INDIAN RESERVATIONlS-PAPAGO TRIBE 

FIGURE 9.-Interbedded reddish fangloonerate and gray conglomerate of the Sil Murk 

forma tion u!Qng northwardctrendong wash In the NW'\4 sec. 2, T. 5 S., R. 5 W. 

solidated and a few thin beds are well cemented with lime. However, 

the unit appears to be consolidated chiefly by bonding rather than 

cementation because most of the calcium carbonate is present along 

fractures and there is little on freshly exposed surfaces of the matrix. 

The larger fragments are composed of rocks derived from the Gila 

Bend Mountains-predominantly gneiSSIC granite a.nd smaller 

amounts of schist, quartzite, granite, and fine-grained dark-colored 

intrusive rocks. There are also a few fragments of felsite of possible 

volcanic origin whose source is not known. The matrix consists of 

silt, sand, and pebbles, and is composed principally of broken feldspar 

and quartz crystals. 

The gray conglomerate is overlain by the volcanic rocks that cornpose the volcanic member of the Sil Murk formation, and it is overlapped by younger alluvial deposits. The total exposed thickness of 

the sedimentary member o:f the Sil Murk :formation is estimated to bP. 

at least 1,500 :feet. It may be thicker in other areas or below the 

surface. 

Many porous lenticular beds occur in the sedimentary member of the 

Sil Murk :formation, and it is one of the principal water-bearing formations in the area, as discussed in the section "Subsurface stratigraphy." Moderate quantities o:f ground water reportedly are 

produced :from the sandstone o:f the Sil Murk :formation by a well 
GROUND WATER, Grr:.A BEND IN:PIAN RESE'RVATION 

about 15 miles west of the reservation (Babcock and others, 1948, p. 

10). This well produced about 150 gpm (gallons per minute) from 

about 600 feet of sandstone below a depth of 1,100 feet. The formations above 1,100 feet were cased off. All other deep wells in the area 

are open both to the Sil Murk formation and the overlying deposits, 

and the production from the Sil Murk formation alone cannot be 

determined. 

VOLCANIC MEMBER 

Volcanic rocks overlie the gray conglomerate in the southernmost 

part of the Gila Bend Mountains, and because of their resistance to 

erosion, they form prominent cuestas and low hills (fig. 3). These 

volcanic rocks constitute the volcanic member of the Sil Murk formation. Volcanic rocks crop out in five areas on the reservation (fig. 4). 

The largest area forms the cuesta that juts into the channel of the Gila 

River at the southernmost point of the Gila Bend Mountains. A 

small outcrop of dacitic welded tuff is exposed south of the river at the 

site of an abandoned pumping station. Three small areas along the 

west flanks of the mountains form small hills. 

Volcanic rocks also underlie the alluvium locally near the mountains. Ross (1923, p. 73 and fig. 14) interprets information from bore 

holes drilled across the channel of the Gila River at the abandoned 

pumping station as indicating that "Tertiary deposits"-the volcanic 

member of this report-underlie the channel fill at shallow depths. In 

his text, Ross reports that "bedrock is less than 160 feet below the 

surface at any place in the channel," but in a scaled drawing, depth to 

"bedrock" is shown as no greater than 60 feet. The volcanic rocks 

may underlie the alluvium below the Gila Bend plain, but have not yet 

been reported from wells drilled to a maximum of nearly 1,500 feet 

beneath the surface. 

The volcanic rocks are considered to be a member of the Sil Murk 

formation because beds of the volcanic rocks are reported by Babcock 

and others (1948, p. 7) to be interbedded with fanglomerate (gray 

conglomerate of this report) 3 miles north of the reservation. Within 

the reservation, however, the volcanic member lies in angular unconformity on an erosion surface of low relief that was cut on the gray 

conglomerate. Along the east front of the cuesta at the south end 

of the Gila Bend Mountains, the gray conglomerate dips at angles 

up to 30° and the volcanic beds dip at 5° to 12°; at the hill in the 

NW1,4 sec~ 9, T. 5 S., R. 5 W., the gray conglomerate dips 5° and the 

volcanic beds dip 10° (fig. 10). All the dips are to the southwest. 

Also, the lowest unit of the volcanic member, an eolian tuffaceous 

sandstone, thickens southward, and this unit and an overlying conglomerate lens in the volcanic member are absent at the hill in sec. 9. 
~ WATER SUPPLY OF INDIAN REiSERVATIONS-PAPAGO TRIBE 

sw. NE. 

FIGURE 10.--J)ia,grammatic section of a small hill in the NW'.4 sec. 9, T. 5 S., R. 5 W., 

showing local angular unconformity between the sedimentary a nd volcanic members of 

the Sil Murk forma tion a nd erosional surfaces within the volcanic member. 

These stratigraphic variations in the volcanic member indicate that 

local relief of about 200 to 300 feet per mile along the strike of the 

deposits had developed on the gray conglomerate member before the 

volcanic member was laid down. The regional significance of this 

unconformity cannot be evaluated from the exposures in the mapped 

area. 

The volcanic member is composed of eolian tuffaceous sandstone, 

dacitic tuff and welded tuff, basalt flows, and intercalated conglomerate lenses. The eolian sandstone is exposed only near the south end 

of the prominent cuesta in sec. 15, T. 5 S., R. 5 W. It is yellowish 

green to light brown and under the hand lens has a salt-and-pepper 

appearance, in which the light fraction is composed of quartz shards 

and altered feldspar(?) fragments and the dark fraction is composed of small cinders, magnetite, and biotite. The eolian sandstone 

varies considerably in its degree of induration. Generally it is friable, but locally it is strongly cemented with calcium carbonate. The 

unit is well bedded and has thin but not persistent laminae. The 

crossbeds have a general northwest strike and dip to northeast. At 

a cursory glance, the eolian tuffaceous sandstone is similar in appearance to the thin-bedded fraction of the sandstone of the sedimentary 

member of the Sil Murk formation. The rocks may be distinguished, 

however, by the presence of tuffaceous material and crossbeds in the 

eolian sandstone in contrast to the comparatively clean arkosic composition and reg~ lar dips of the lower sandstone. 

The eolian sandstone is overlain by a 4-foot-thick flat-lying laminated ash bed that transects the more steeply dipping crossbeds of 

the eolian sandstone (fig. 11). The ash bed is brownish red to light 

buff, and flecked with dark-brown or black biotite grains. The ash 

bed is overlain by dacitic welded tuff that forms the cliff capping the 

cuesta at the south end of the Gila Bend Mountains (fig. 12) . The 

lower 2 feet of the welded tuff is a black glassy vitrophyre which 

weathers into rough slabs and grades upward into a welded tuff hav-
GROUND WATER, GILA BEND INDIAN RESERVATION A17 

FIGURE 11.--<Contact between the crossbedded eolian tuffaceous sandstone and the ush· 

bed at the base of the dacitic welded tuff of the volcanic member of the Sll Murk forma -

tion in the NW:Y. sec. 15, T. 5 S., R. :J W. 

FIGURE 12.-,Dacitic welded tuff showing ma ssh·e welded tuff, slabby vitrophyre, and basal 

ash boo of the volcani c member of tile Sil Murk formation in the N\.Ylj, sec. 15, T. 5 S., 

R. 5 W. 
A18 WATER SUPPLY OF INDIAN RESERVATIO:NlS-"-PAPAGO TRIBE 

ing a cryptocrystalline instead of a glassy groundmass. The welded 

tuff weathers brown, but on the fresh surface it is grayish lavender to 

brownish red. It is composed of quartz and feldspar crystals, flattened pumiceous fragments, and scattered angular rock fragments in a 

vuggy cryptocrystalline matrix. Some of the ,rock fragments appear 

to be andesitic. There is a rough alinement of feldspar crystals and 

pumiceous fragments parallel to the bedding, but the unit is massive. 

At the cliff face the rock breaks into irregular fragments irrespective 

of the fragment alinement, but on dipslopes it tends to spall more or 

less parallel to the bedding. 

The conglomerate lenses in the volcanic member are composed 

largely of crystalline-rock fragments similar to those of the gray 

conglomerate. At the north end of the exposure of the volcanic 

member in sec. 10, T. 5 S., R. 5 W., the conglomerate lens appears to 

interfinger with the gray conglomerate, but the contact area is covered 

by a heavy rubble, derived from the cliffs of dacite and the underlying 

conglomerate, and the relationship is not exposed. 

Two sections, measured by Brunton compass and pace traverse, are 

described below. The dacitic welded tuff that forms the cap of the 

cuesta in sec. 10, T. 5 S., R. 5 W. is correlated with the dacitic welded 

tuff at the base of the section in sec. 9 (fig. 10), and the units are 

numbered consecutively from bottom to top. 

Section 1. Vokanic member at th.e sooth end of the Gila Bend Mountain.s in 

sec. 10, T. 5 8., R. 5 W. 

Tertiary: 

Erosion surface (essentially a dipslope on unit 3). 

Sil Murk formation: Thickness 

Volcanic member (strike, N. 55° W.; dip, 5° SW.) : (feet) 

3. Dacitic tu1f and welded tuff: lavender to brownish-red, 

weathering brown; in units about 20 to 30 ft thick that 

contain thin black basal vitrophyre beds ; locally underlain by about 4 ft of thin-bedded brownish-red to lightbuff ash ·at the base; forms cliffs---------------------- 50± 

2. Conglomerate : gray ; small boulder to small pebble ; contains fragments of volcanic rocks of intermediate composition in addition to granite, gneiss, and schist fragments which predominate ; forms poorly exposed slopes 

covered by scree from overlying dacite ; lenticular, 

pinches out at the northern and southern ends of the 

cuesta and apparently fills a channel cut into unit!____ 0-150± 

1. Tuffaceous sandstone: gray, yellow-green, light-brown; 

thin-bedded ; :flecked with biotite; characterized by irregular dips and strikes that suggest eolian crossbedding __ 30-150± 

Maximum measured thickness of volcanic member -------------------------------·--------- 175± Angular unconfol'mity. 

Gray conglomerate. 
GROUND WATER, GILA BEND INDIAN RESERVATION Al9 

Section 2. Volcanic member on the small hill in the NE1J4 sec. 9, T. 5 S., R. 5 W. 

Tertiary: 

Erosion surface. 

Sil Murk formation: 

Volcanic member (strike, N. 55° W.; dip, 10• SW.) : 

6. Tuff: lavender; fine-grained, possibly dacitic; forms small 

blocky exposure on west end of dipslope ridge _______ _ 

5. Conglomerate: gray; fragments of both gneissic and volcanic rocks ; pebble to small cobble, few gneissic boulders 

as much at 4 ft. in maximum dimension; forms slopes __ 

4. Basalt: black ; fine-grained, containing small red-brown 

blebs up to 1 mm in width of iddingsite( ?) ; wedges out to 

east ------------------------------------------------ 3. Dacitic welded tuff: gray to light-lavender, biotite 

speckled; massive; forms prominent cliff at east base 

of hil'-----------------------------------------------

Maximum measured thickness of volcanic 

member 

Low angular unconformity. 

Sedimentary member. 

Thickness 

(feet) 

15± 

70± 

0--10± 

20± 

115± 

The exposure in the NW:J,;4SW% sec. 10, T. 5 S., R. 5 W. contains 

basalt that is similar to the basalt described above. 

There are no wells or springs in these volcanic rocks and the interbedded conglomerate. Except -for the basalt, the volcanic rocks seem 

to be nearly impervious and cannot be considered favorably as potential aquifers, except where they may be highly -fractured. The interbedded conglomerate beds, howeverl are porous and many carry 

moderate supplies of ground water below the water table. 

CORRELATION, AGE, AND ORIGIN 

The Sil Murk -formation is the -fanglomerate unit described by 

Babcock and others (1948). However, the correlation of the Sil 

Murk -formation with the Locomotive fanglomerate in the Ajo 

area (Gilluly, 1946) suggested by Babcock and others (1948, p. 3) is 

questionable -for lack of corroborative information and because of the 

differences between the two units. Their principal similarities are 

that both units lie in depositional contact on gneissic rocks and that 

both are composed of deformed alluvial--fan deposits. Neglecting 

differences in color and composition, which -for a single unit may vary 

widely -from place to place, the principal differences are stratigraphic 

position relative to overlying deposits, degree of structural deformation, and degree o£ alteration. The Locomotive -fanglomerate is 

overlain by five mappable units and is separated -from the alluvium 

that partly fills the adjoining basin by -four erosional or angular unconformities (Gilluly, 1946); the sedimentary member of the Sil Murk 
A20 WATER SUPPLY OF INDIAN REiSERVATIONl8-PAPAGO TRIBE 

formation is overlain by only the volcanic member and is separated 

by only one unconformity from the alluvium that underlies the Gila 

Bend plain. The Locomotive fanglomerate has been extensively 

deformed-possibly thrust faulted (E. D. Wilson, oral communication, 1957)-and has undergone weak hydrothermal alteration locally; 

whereas the Sil Murk formation has been warped and folded only 

mildly and is unaltered. Furthermore, north of the reservation the 

Sil Murk formation strikes toward the "older volcanic rocks" mapped 

by Babcock and others ( 1948, pl. 1). Reconnaissance in the area suggests that the Sil Murk formation eithe'r underlies or is contemporary 

with the "older volcanic rocks," and that the "older volcanic rocks" 

are lithologically and structurally similar to the Batamote andesite in 

the Ajo area (Gilluly, 1946). Mapping of the Papago Indian Reservation supports but does not prove this correlation. Consequently 

the Sil Murk formation is tentatively considered to be younger than 

the Locomotive fanglomerate, although correlation with the Locomotive cannot be absolutely precluded at this time. In their similarities and differences, the two deposits reflect the tremendous intricacy 

of local control in the development of Cenozoic geology in southern 

Arizona, and it is preferable to give them discrete identities until their 

equivalence can be demonstrated. 

The Sil Murk formation dips gently to the southwest and its dipslopes have resulted from the westward tilting of the Gila Bend 

Mountains fault block. The composition of the conglomerate fragments also indicates its direct derivation from the crystalline core of 

the Gila Bend Mountains as they were uplifted and tilted. This 

faulting is generally considered to be of late ( ? ) Tertiary to Quaternary age (Wilson and Moore, 1959) . However, the Sil Murk formation appears to pass under the older alluvial fill of the Gila Bend plain 

which is tentatively considered to be of possible Pliocene and Pleistocene age. Furthermore, north of the mapped area the volcanic member appears to underlie or be a part of the extensive deposits of the 

"older volcanic rocks" described by Babcock and others (1948). 

Regional consideration of the age of the "older volcanic rocks" 

and related deposits suggests that they either antedate or are contemporaneous with the major expression of basin-and-range faulting. 

Consequently a late middle(?) Tertiary age for the Sil Murk formation seems to be tenable at this time. 

The change in color, texture, and fragment size from the basal 

arkosic sandstone to the gray conglomerate occurs gradually through 

the transitional fanglomerate that lies between them. This fact sug-
GROUND WATER, GILA BEND INDIAN RESE·RVATION A21 

gests that the Sil Murk formation represents a time of gradual chan~ 

in local environment which, in turn, reflects the uplift of the Gila 

Bend Mountains fault block. Probably elsewhere in the region the 

transitional. zone between the sandstone and conglomerate is represented by erosional or angular unconformities. The red fine-grained 

arkosic sandstone suggests flood-plain deposition in an area of low 

relief; the considerable thickness of the gray boulder conglomerate 

suggests deposition from a rapidly rising nearby highland. The volcanic member indicates volcanic activity contemporaneous with the 

uplift. 

TERTIARY AND QUATERNARY ALLUVIAL Dl!WOSITS 

The material that partly fills the basins around the mountains and 

overlaps the lower slopes of the mountains is collectively referred to as 

alluvium. The critical distinction between these alluvial deposits and 

the Sil Murk formation which was also deposited as alluvium is th11-t 

the alluvial deposits were laid down within the basins that are present 

today, whereas the Sil Murk formation was laid down in basins that 

have disappeared. 

The alluvium is composed of poorly consolidated gravel, sand, silt, 

and clay that were deposited as irregular overlapping lenses by stream 

action or sheetflow, or as small to large discontinuous fine-grained 

lenses in ephemeral ponds and lakes or backswamp areas. The JTI.fl~ 

terials are poorly to well sorted, and the sorting in adjacent lenses may 

differ radically. Two major groupings of .alluvial. deposits are 

exposed at the surface. 

From their surface exposures the a1luvial deposits can be grouped 

into two units: older alluvial fill and younger ~lluvial· fill; these· deposits represent two late stages in the depositional history of the ba.Sinfill deposits. A moderate thickness of alluvial material underlying 

the Gila Bend plain is known only from well logs, and it is arbitrarily 

included in the older alluvial fill~ although parts of it may be much 

older than the part exposed at the surface. 

The contact between the older and younger alluvial fills is dr~wn 

arbitrarily along the foot of the terraced surface that forms tile Gila 

Bend plain, and delineates some of the more recent floOd-plain deposits 

of the Gila River from the materials into which the river is entrenched. 

Three sets of terraces above the present flood plain and more or less 

parallel to the river were mapped by Kendall (in Ba·bcock and others, 

1948, pl. 1). Only the younger two are exposed within the area shown 

on figure 4 and they are not delineated as·:terraces. They. are mapped _,. .'-· ~; 

6149978 Q-63---4 
A22 WAT,ER SUPPLY OF INDIAN REiSERVATIONIB-PAPAGO TRIBE 

as part of the older alluvial fill and form low dissected discontinuous 

benches along the contact of the older and the younger alluvial fills. 

The terraces are covered by a deposit of silt, sand, and small rounded 

pebbles that· ranges from a thin veneer to a few feet in thickness. 

They are above the water table everywhere in the area. 

OLDZB.,:.Al.LUV.IAL ... :UL.L 

The exposed parts of· the older·alluvial fill include conglomer~te in 

the dissected alluvial fans that crop out along the flanks of the Gila 

Bend Mountains, thin terrace deposits, and deposits of generally fine 

grained gravel, sand,. and silt that underlie the Gila Bend plain. 

Presumably, the latter are continuous with the subsurface part of the 

older alluvial fill, which 'is predominantly sand, silt, and clay. Near 

the mountains the older alluvial fill rests unconformably on an erosion 

surface cut on crystalline rocks and the Sil Murk formation. · In this 

zone it is seldom more than 50 feet thick. Under the Gila Bend plain, 

the thickness of the older alluvial fill is estimated to range from about 

300 to.500 feet. The subsurface stratigraphy is discussed in a following section. 

The age of the older alluvial fill cannot be proved but it probably 

spans the Tertiary-Quaternary boundary. The predominantly sand, 

silt, and clay deposits of the older alluvial fill seem to be lithologically 

and structurally similar to thick fine-grained deposits in other areas 

of Arizona. NearSafford the exposed parts of such deposits are of 

Blancan (Pliocene-Pleistocene) age ( Gazin, 1942), and near Benson 

and north along the San Pedro Valley they range in age from midPliocene through early Pleistocene ( Gazin, 1942; Lance, 1960). The 

older alluvial fill in the Gila Bend basin may be of similar age. 

Babcock and others (1948, p. 8) presume that much of the valley 

fill may have accumulated when the basin had no through drainage; 

but similar deposits may be laid down by poorly integrated or sporadic 

drainage. However, they presumed a considerably thicker older alluvial fill than is described in this report. At the present time, the 

subsurface· geology of the Gila Bend area is not well enough known to 

demonstrate the presence or absence of bedrock barriers at altitudes 

sufficient to result in internal drainage in the Gihi Bend area in late 

Tertiary and Quaternary time. 

Moderate to large quantities of ground water are obtained from 

the older alluvial fill, but its productivity cannot be separated from 

that of the younger alluvial fill and the underlying formation because wells that produce from the older alluvial fill are perforated 

to be open also to one or both of the other units. 
GOOUND WATER, GILA BEND INDIAN RESERVATION A23 

YO'O'NGEll ALLUVIAL FILL 

Flood-plain and channel deposits of the Gila River comprise the 

younger alluvial fill. These deposits are entrenched into the older 

nlluvial fill and are clearly related to the present and near-recent 

regimen of the Gila River. The younger alluvial fill is composed of 

silt, sand, and gravel, and is in general less consolidated than the older 

alluvium. The channel deposits are unconsolidated. The younger 

alluvial fill commonly is finer than the exposed parts of the older 

alluvial fill near the mountains and coarser than the older alluvial 

fill into which it is entrenched. 

· The flood-plain deposits form n broad swath through the center 

of the area mapped, and are reported to be as much as SO feet thick 

(Babcock and others, 1948, p. 9). The more permeable>sahd and 

gravel layers of the flood plain are highly productive aquifers. Their 

separate yield is not known because no irrigation wells in the area 

produce from the younger alluvial fill alone. The combined aquifers 

locally yield more than 3,000 gpm. 

SUBSURFACE .. STRATl:GBAPHY 

Deep wells are the only source of information about the sedimentary 

deposits and older rocks underlying the Gila Bend plain. Information regarding these wells is obtained from drillers' logs (table 1) 

and from one partial set of well cuttings. It is difficult to correlate 

the drillers' logs, partly because of the highly variable character of 

the alluvial materials and partly because of the differences in judgment and nomenclature of the several drillers. Furthermore, it is 

often difficult in drilling to determine the point at which significant 

changes in the formations occur. Nevertheless,.the'major changes in 

lithology can be identified by interpretation of the drillers' logs in 

the light of the information gained from the available well cuttings. 

On this basis, the following interpretation of the subsurface stratigraphy is offered. 

Babcock and others (1948) and Ross (1923) suggest that the older 

alluvial fill is 1,100 feet thick in the vicinity of Gila Bend. On the 

basis of information from more recent logs and the drill cuttings, it 

is suggested that only 300 to 500 feet of the rocks penetrated by the 

drills in the area mapped is older alluvium and that the materials 

below these depths are part of the Sil Murk formation. 
A24 WATER SUPPLY OF INDIAN RE,SERV:ATIONlS-PAPAGO TRIBE 

TABLE 1.-Drillers' logs, eiJJeept as indicated, 6t selected wells in the vicinity af 

Gila Bend Indian Reservation, Maricopa Oounty Ariz. 

[Asterisks (*)indicate postulated break between older alluvial fill and eon~lomerate of Sil Murk formation. 

Plus symbols ( + J indicate postulated break between eonglomerate and sandstone of Sil Murk formation] 

Thick- Depth ness (feet) (feet) 

T. 5 S., R. 4 W. 

SE%SE7mE% sec. 18: 

Sandy silt ________ 18 18 Sand _____________ 6 24 

Sand and gravel 

with a little clay ____________ 

Sand, gravel, and 

6 30 

boulders ________ 

Strata of clay and 

sand (from 24 

24 54 

to 100 is water 

bearing) ________ 46 100 Dry clay _________ 22 122 

Clay and strata of 

sand (water) ____ 82 204 Dry clay _________ 6 210 

Sandy clay with 

small gravel (water) _________ 40 250 Dry clay ______ - __ 10 260 

Strata of clay, 

packed sand, and sand _______ 20 280 

Strata of cemented 

sand and sand ___ 20 300 Sandy clay ________ 

Strata of cemented 

20 320 

sand, sand, and ' small graveL ____ 

Strata of clay and 

10 330 

sand ___________ 14 344 Sandy clay ________ 66 410 

Strata of dry clay 

and sandy clay . ·(from 280.,.422 

has some water)_ 12 422 

Strata of sandy 

.clay anq sand-

·stone ___________ 18 440 

Dry clay"---~---- 12 452 

Sandy clay . 

18 470 (water?) ________ 

Clay with small 

·.• .. ··· .. : gravel (dry:) _____ 31 501 --- SE%SE7~SEH sec. 19: Soil ______________ 3 3 

Silt, gravel, clay ___ 15 18 

Sand, small graveL 16 34 

Sand, gravel, boulders ________ 6 40 

Sand, sandstone, clay ____________ 

Strata of sand, 

50 90 

clay ________ - - - - 74 164 

T. 58., R. 4 W.-Con. 

SE%SEJ,~SE7~ sec. 19-

Continued 

Sand, small gravel 

with strata of 

cemented sand __ 

Strat~t of sand, 

gravel, clay, 

cemented sand __ Dry clay _________ 

Sandy clay with 

strata of sand rock ___________ 

Dry clay _________ 

Strata of clay, 

sand, cemented 

sand, water _____ Dry clay _________ 

Strata of clay, 

sand, sandstone 

(water) _________ Dry clay _________ 

Sandy clay with. 

strata of dry 

clay; some water 

in sandy clay ____ 

Dry clay with 

small graveL ____ Dry clay _________ 

Strata of sand clay 

a.,nd cemented 

sand; some water_ " __ ------ Dry clay __________ 

Silty clay, a little 

water-------' __ -_ Dry clay ________ -

Strata of clay, pack 

sand, and small 

gravel (water) ___ Dry clay ____ ~ ____ 

* * * 

Strata of sand, 

gravel, cemented 

sand, graveL ____ Strata of clay, 

sand, gravel, 

cemented sand, graveL _________ 

Strata of sand, 

gravel, clay with 

mountain rock ___ Mountain wash 

sand and 

mountain rock ___ 

Thickness 

(feet) 

21 

51 

19 

71 

14 

42 

9 

49 

11 

49 

20 

. 58 

6 

46 

20 

6 

34 

10 

38 

20 

43 

125 

Depth 

(feet) 

18 

23 

25 

32 

5 

6 

5 

34 

6 

0 

38 2 

39 1 

44 0 

45 1 

50 0 

0 

8 

52 

57 

58 4 

63 0 

65 

65 

69 

\70 

73 

75 

0 

6 

0 

0 

8 

8 

8 01 

92 6 
GROUND WATER, GILA BEND INDIAN RESERVATION A25 

TABLE l.-DriUers' logs, emcept aJJ indicated, of selected wells in the vicinity of 

Gila Bend Indian Reservation, Maricopa Oown.ty, Ariz.-Continued. 

Thick· Depth ness (feet) (feet) 

Thick' Depth ness (feet) (feet) 

-----------------t-----1-----ttt-----------------t·---------

T. 5 S., R. 5 W. 

SE~SE~NW~ sec. 18: Clay ____________ _ 

Boulders and graveL ________ _ 

GraveL __ -------- Clay with streaks 

of sand ________ _ 

ClaY-------------

Hard sand, dark __ _ Dark sand _______ _ Clay ____________ _ 

+ + + 

Hard sandy shale __ 

NW~SW%SE~ sec. 18: 

Surface sand and graveL ________ _ 

Small gravel with 

streaks of clay--- Clay _____________ _ 

Light-colored sand 

and graveL ____ _ Clay _____________ _ 

Sand and gravel with 

streaks of clay __ _ 

* * * 

Gray clay embedded with graveL_ 

Sand with streaks 

of clay ___ - ___ - - -

Sand and graveL __ 

+ + + 

Black sand and graveL ________ _ 

Red graveL ______ _ 

SW%SE7~SE%sec.18-1: 

Surface sand and 

graveL ________ _ 

Fine sand with 

streaks of clay __ _ 

* * * Sand ____________ _ 

Coarse sand ______ _ Clay _____________ _ 

Sand, coarse, with 

streaks of clay __ _ Sand and graveL __ 

+ + + 

Hard sand _______ _ 

Black sand, hard __ Brown sand ______ _ Dark sand _______ _ 

ClaY-"-----------

40 40 

42 82 

480 562 

212 774 

21 795 

20 815 

10 825 

10 835 

30 865 

45 45 

195 240 

20 260 

20 280 

80 360 

170 530 

40 570 

200 770 

70 840 

100 940 

20 960 

312 312 

178 490 

105 595 

20 615 

125 740 

49 789 

44 833 

16 849 

37 886 

55 941 

59 1, (]100 

31 1, (]131 

T. 5 S., R. 5 W.-Con. 

8WHSEJ4SEH sec.18-2: 

Sandy clay _______ _ 

Gravel and 

boulders _______ _ 

Sand, gravel, and 

boulders ___ - ___ _ 

Gravel and clay __ _ Gravel and clay __ _ Sand and graveL __ Sand and graveL __ Sand and gravel 

with some rock 

and clay _______ _ 

SEHSEHSWH sec. 22: 

TopsoiL _________ _ 

Gravel and boulders_ 

Sand with clay streaks ________ _ 

* * * 

Mildly rocky dark 

in color ________ _ 

Solid red rock, mild_ 

+ + + 

Hard-packed sand_ 

Coarse sand with 

graveL ________ _ 

Clay with sand ___ _ 

Sand with gravel streaks ________ _ Sandy clay _______ _ 

Cemented sand ___ _ 

SW7~SW7~SE% sec. 23 

(log based on wellcutting sample 

analysis): 

Light-reddishbrown silt with 

arkosic sand ___ - Light-reddish- brown silt _____ _ 

* * * 

Coarse sand to 

granule gravel; 

fragments predominantly 

quartz and 

feldspar, some granitic rock 

and minor 

amounts of 

magnetite ____ ---

45 

30 

80 

50 

95 

125 

175 

200 

5 

70 

225 

120 

217 

313 

80 

220 

60 

73 

64 

325 

125 

100 

45 

75 

155 

205 

300 

425 

600 

800 

5 

75 

300 

420 

637 

950 

1, 030 

1,250 

1, 310 

1, 383 

1,447 

325 

450 

505 
A26 WATER SUPPLY OF INDIAN REiSERVATION18-PAPAGO TRIBE 

TABLE 1.-Drillers' logs, eiJJcept as indicated, of selected, wells in the vicinity of 

Gila Bend Indian Reserv>ation, Maricopa County, Ariz.-Continued 

Thick- Depth Thick- Depth ness (feet) ness (feet) (feet) (feet) 

------- T.5S.,R.5 W. T. 5 S., R. 5 W.-Con. 

SWHSWHSEH sec. 23- SW~~SW7~SE7~ sec. 23- Continued Continued 

Same as 550-ft. About half the 

sample, but material com- finer grained posed of reddish 

and contains and grayish more magnetite_ 50 600 sandstone; redSame as 550-ft dish sandstone sample _________ 150 750 is fine grained, 

+ + + arkosic, with 

biotite flakes; 

Medium-grained gray sandstone 

subangular to is fine grained, 

subrounded arkosic; bedding 

sand contain- plane with gray 

ing fragments mudstone in one 

of moderately fragment; sandcemented light- stone lightly 

reddish-brown cemented with 

arkosic sand- lime; no granitic 

stone and bio- fragments _______ 25 1, 425 

tite flakes; Same as 1,425-ft. 

some granitic sample _______ -- 50 1, 475 

fragments and --- SWXSW%SE7~ sec. 24: one piece of red TopsoiL __________ 30 30 volcanic(?) rock ___________ Coarse sand and 200 950 graveL _________ 240 270 Same as 950-ft 

sample; mag- Sandy clay ________ 220 490 

netite common __ 225 1,175 * * * Same as 950-ft. Cemented sand ____ 120 610 

sample except Sand and boulders_ 240 860 

almost no mag- Sand, clay, and 

netite; few frag- 1, 085 graveL _________ 225 

ments of buff + + + tuffaceous(?) Clay _____________ sandstone _______ 145 1, 230 125 1,300 Gravel, cemented Same as 950-ft. 1, 400 sample; several 

sand ___________ 170 

reddish sand- --- stone T.5S.,R.6 W. fragments _______ 75 1, 375 

Same as 950-ft NWXNW7~SEXsec. 11: 

sample; frag- Surface sand and 

ments of reddish 

Cl~~~::~========= 40 40 

sandstone up to 435 475 

half an inch in Small graveL _____ 122 597 

maximum Clay _____________ dimension ______ 25 1, 400 * * * 13 610 

Small graveL _____ 80 690 

Clay and graveL - _ 38 728 

Small graveL _____ 172 900 

+ + + 

Hard fine sand ____ 20 920 
GROUND WATER, GILA BEND INDIAN RESERVATION A27 

The estimate of thickness was revised for the following reasons: 

Most logs report materials described as "black sand, hard," "red 

gravel," or "cemented sand" at depths greater than 850 feet. These 

descriptions better fit the lower facies of the sedimentary member of 

the Sil Murk formation than either the gray conglomerate of the Sil 

Murk or older alluvial deposits. Furthermore, drill cuttings from the 

well in sec. 23, T. 5 S., R. 5 W. contain many fragments of lightreddish-brown sandstone from 950 to 1,475 feet. This sandstone is 

identical with sandstone in the lower facies of the sedimentary member 

of the Sil Murk formation. Fragments of the sandstone, both from 

surface exposures and from drill cuttings, are very friable. Because 

the fragments are so numerous and so friable, it is not likely that they 

represent pebbles or cobbles of the sandstone from either the gray 

conglomerate or the older alluvial fill. Consequently, the material below about 850 feet is presumed to re.present the lower facies of the 

sedimentary member of the Sil Murk formation in place. Above the 

lower facies there is a zone about 500 feet thick. The zone is generally described in the well logs as "sand and gravel," or "sand and 

boulders," with only a few references to "clay." This zone is considered to be the gray conglomerate of the Sil Murk formation because 

the gray conglomerate is more resistant than the sandstone facies and 

more likely would have been the unit preserved as caprock during 

the erosion interval that preceded the deposition of the valley fill. 

The upper 300 to 500 feet, except for the near-surface deposits, are 

generally described as containing considerable "clay" and these deposits are assigned to the older alluvial fill. The relationships are 

shown graphically in figure 13. 

The older alluvial fill is believed to have been deposited on an old 

eroded surface cut on the Sil Murk formation. The erosion surface 

dipped away from the mountains, gently to the west and south and 

somewhat more steeply to the east. The extent of this bench outside 

of the area mapped is beyond the scope of this investigation. 

STRUCTURE 

The regional structural relations of the Gila Bend area are described by Babcock and others ( 1948, p. 6) as follows: 

The valley that lies between the Maricopa Mountains and the Gila Bend and 

Sand Tank Mountains [fig. 2l appears to be a structural trough with faults 

along the east and west sides. The scarps on the west side of this valley, particularly along the southeastern part of the Gila Bend Mountains, are relatively 

high, steep, and straight, suggesting that some of the faulting i~ recent. The 

Gila Bend and the Sand Tank Mountains, which are on the west side of the 

supposed trough, lie along a structural axis which trends northwest. The 

existence of this structural axis is indicated by the alinement and uniform trend 
s M 

--?--

o ' m 

<;,oo' 

\e~ \ s•" 

_<;,oo' 

oo0' 

~'"'oo' 

Well,sec .22 We ll sec.23 Well,sec.24 __ T~S i...Y! ·? 

Ol der rocks'---

500' 

Sea level 

-500' 

-1000' 

~--------------------------------------------------------------------------------------J_ 1500 ' 

FIGURE 13.- Generallzed block diagram with sections through the Gila Bend Mo unta ins and Gila Bend plain, showing postulated r ela· 

tionships between crystalline rocks .• sandstone, conglomerate, and the volcanic facies of the Sil Murk formation, and undifferentiated 

olde r a nd younger alluvial fills. "Older rocks" indica·te the possibility of rocks older than the Sil Murk formation and younger than 

crystalline rocks. Block is brok<'n along line A-A' shown on figur e 4. 
GROUND WATER, GILA BEND INDIAN RESERVATION A29 

of the two mountain ranges ; by the similarity in the two mountain range& of 

a granitic core, :flanked on the west by fanglomerate and interbedded rocks; and 

by well logs that show the presence of fanglomerate and interbedded rocks 

beneath the alluvial :fill at Gila Bend. Other evidences are the major fault on 

the east side of the two mountain ranges and scarps in the relatively weak 

fanglomerate that suggest recent faulting parallel to the grantitic core. 

Structural details of the Sauceda and the Painted Rock Mountains also show 

the northwest-southeast trend that is characteristic of the greater part of the 

Gila Bend area, although the evidence is not as strong as in the Gila Bend and 

the Sand Tank Mountains. The older volcanic rocks in the northern part of the 

Painted Rock Mountains strike northwest, forming hogbacks that cross the 

north-trending range. Likewise, in the northern part of the Sauceda Mountains, the outcrop pattern of both the older volcanic rocks and the Cardigan(?) 

gneiss trends northwest. Along the northeast side of the Sauceda Mountains 

discontinuous outcrops of a distinctive basalt may be exposures of dikes. The 

outcrops trend northwest in line with outcrops of similar rock, outside the 

mapped area, in the northwest part of the Painted Rock Mountains. All these 

outcrops may be parts of the same dike system. Between the two mountain 

ranges there are small outcrops of the older volcanic rocks. 

The criteria described above and the moderate westward dip of the 

Sil Murk formation indicate that the Gila Bend Mountains are a 

tilted fault block, upthrown on the east side and sloping back to the 

west. Some of the materials penetrated at depths of nearly 850 feet 

in sec. 18, T. 5 S., R. 5 W., are correlated with the Sil Murk formation, 

and thus the Gila Bend Mountains seem to extend as a single block to 

at least the vicinity of sec. 18 (fig. 4). Ross (1923, p. 73 and pl. 11) 

also suggests that the mountain block extends under the alluvium 

toward Gila Bend. 

Small faults, either parallel or transverse to the trend of the mountains, occur locally within the Sil Murk formation but are not shown 

onfigure4. 

GEOLOGIC mSTORY 

The schist and gneiss of probable early Precambrian age represent 

ancient sedimentary, volcanic, and igneous rocks that had been deformed, intruded, and beveled by erosion, possibly several times, before the deposition of the red arkosic sandstone in Tertiary time. 

Information from nearby areas suggests also that some granitic intrusions may have occurred during early Precambrian time, but the 

age of the granite in the Gila Bend Mountains has not been determined and possibly some of it may have been intruded after the 

deposition of Paleozoic strata. 

Shallow seas covered the area during much of the late Precambrian 

and Paleozoic time, and a few thousand feet of limestone and smaller 

thicknesses of mudstone and sandstone were laid down. During most 

of Mesozoic time the area was being- deformed and eroded. It was 

deformed and elevated into mountains or high-standing areas, pos-
A30 WATER SUPPLY OF INDIAN REISERVATIONI&-PAPAGO TRIBE 

sibly in more than a single pulse. The deformation possibly was accompanied by the intrusion of granite which locally may have engulfed the Paleozoic strata. Some of the mountains were high and 

rugged, and the area stood above sea level for a long time, and the 

Paleozoic rocks were completely stripped from the area. 

By late Mesozoic or early Tertiary time only the crystalline rocks 

were exposed over much of the area. Erosion had left a moderately 

rough terrain over which large quantities of andesistic and rhyolitic 

flows, tuffs, agglomerates, and sediments were laid down. As the 

volcanic materials accumulated, locally filling the deeper depressions, 

the relief became more subdued. These deposits were poured out 

spasmodically, and they were accompanied by the intrusion of small 

granitic bodies; locally the volcanic activity was interrupted by 

periods of quiet. 

The sediments constituting the sandstone facies of the Sil Murk 

formation were deposited on a flood plain within a drainage area of 

low relief in the vicinity of the Gila Bend Mountains. Uplift of the 

crystalline core of the mountains occurred along structural lines more 

or less parallel to the trend of the present mountains, and the increased relief provided the coarse debris that is interbedded with the 

fine-grained deposits in the fanglomerate of the Sil Murk formation. 

The uplift oft he Gila Bend Mountains continued, and the old drainage 

system which brought in the fine-grained sediments was either diverted 

away from the area or obliterated. The drainage in the area became 

consequent on the backslopes of the rising Gila Bend Mountains and 

the coarse gray conglomerate was laid do·wn. The deposition of the 

coarse deposits was punctuated by volcanism, one result of which was 

deposition of the volcanic member of the Sil Murk formation in the 

area mapped. To the north, however, a much thicker sequence of 

flows was laid down. 

During late Tertiary time, episodic uplift and movement along 

normal faults on the east side of the Gila Bend Mountains tilted the 

fault block to the west. The tilting led to the erosion of the Sil Murk 

formation down to the gray conglomerate, and led to the development 

of broad valleys around the Gila Bend Mountains far away from 

their present fronts. The slopes of the late Tertiary Gila Bend 

Mountains dropped gradually toward a valley floor to the south. The 

gradients of these slopes 'vere such that at distances of :3 to 5 miles 

from the present mountain fronts, the ancient ground surface was 300 

to 500 feet below the present floor of the Gila Bend plain. 

Deposition of the older alluvial fill in the low areas around the Gila 

Bend Mountains began in late Tertiary and continued through most of 

the Quaternary. The reasons :for the change :from dissection to 

aggradation are not known, but the change was regional in character 
GRJOUND WATER, GILA BEND INDIAN RESERVATION A31 

and may have been related to regional tilting or subsidence, or climatic 

change, or a combination of these factors. The coarse- to fine-grained 

deposits of the 300 to 500 feet of older alluvial fill underlying the Gila 

Bend Indian Reservation and the immediately adjacent area were 

laid down in a broad basin having poorly integrated but through 

drainage, with an outlet probably around the south end of the Painted 

Rock Mountains. The gradient of the drainage was so low that minor 

changes in stream regimen produced temporary lakes within which 

predominantly clay bodies were deposit,ed. 

During this time the region sank slowly relative to the surrounding 

areas, and the top of the late Tertiary-Quaternary deposits in the 

Gila Bend area is at an altitude of about 700 feet, whereas the top of 

the late Tertiary-Quaternary deposits along the lower Colorado River 

is now at an altitude of about 1,100 feet. 

Subsequently, the ancient Gila River developed through drainage 

across the basin and began its present cycle of downcutting and deposition. Babcock and others ( 1948, p. 4-5) describe this interval as 

follows: 

Volcanic eruptions produced cones and basalt flows [not exposed in the area 

of this report] that are associated with the three terraces formed by the Gila 

River as it deepened its valley in the Yalley-fill deposits. Some of the lava flows 

dammed the river temporarily. One of theRe dam,;, made during the forming of 

the highest (oldest) terrace by lava from a cone im the northern part of the 

Painted Rock Mountains [fig. 2], diverted the river around the southern end 

of these mountains. This diversion of the riYer is indicated by the extension 

of the highest terrace toward the southern end of the Painted Rock Mountains. 

The river was also dammed at the site of Gillespie Dam by a lava flow from 

·woolsey Peak to the west, which may have diverted the riYer through the Gila 

Bend Mountains. This basalt flow occurred before the lower terrace was cut, as 

it lies on either the upper (oldest) terrace, or the middle terrace, and caps a cut 

bank above the lower (youngest) terrace. 

Additional cones and flows were formed at about the same time. The deposits 

capping the middle terrace contain a layer of ash produced during these 

eruptions. 

Records of wells indicate that, after the surface of the lower terra<"e was cut 

and a thin veneer of grayel was deposited on it, the Gila River <"Ut a Yalley about 

80 feet deep that was then partly refilled with unconsolidated silt, sand, and 

grayel. The present Gila River channel and flood plain were than cut in this 

material. The braided channels of the Gila River lie 5 to 15 feet below the flood 

plain in an inner valley about one-half mile wide. The stream is now building 

up this inner Yalley with alluvium. 

WATER RESOURCES 

The Gila Bend Indian Reservation, compared to many other parts 

of the Sonoran Desert, is favorably located in regard to water supply 

because it as astride the Gila River. Even though flow in the Gila 

River is rare, an ample supply of ground water is easily available, 
A32 WATER SUPPLY OF INDIAN RESERVATIONlS-PAPAGO TRIBE 

although its quality may be poorer than is desired. In contrast, in 

the mountain areas ground water is scarce or nonexistent. 

SURFACE WATER 

The Gila Bend Indian Reservation includes a 6-mile reach of the 

Gila River which is dry or nearly dry, except during floods. Streamflow records of the Gila River below Gillespie Dam (U.S. Geol. Survey, reference a) show that the long-term, 1922-58, average flow is 

about 186,000 acre-feet per year. During this period flow ranged from 

less than 100 to more than 1,0~0,000 acre-feet per year. From 1922 

to 1941, the average annual flow was about 325,000 acre-feet per year 

ap.d flow in only 3 of the 20 years was less than 25,000 acre-feet. In 

contrast, the average annual flow during 1942-58 was about 23,000 

acre-feet per year and in only 3 of the 17 years was the flow greater 

than 25,000 acre-feet. The lower flow since 1941 is due primarily to 

drought conditions and secondarily to additional upstream storage and 

diversion. 

The Gila River was not always so barren of flow. Early writers 

refer to subsistence fishing, diversions for irrigation, rafting to Yuma 

down the Gila from above its junction with the Salt River, and to 

thickly overgrown banks teeming with geese, ducks, deer, and beaver 

(Ross, 1923, p. 64-67). In regard to a contrast drawn by an early explorer between the "reddish water" of the Colorado and the "sea green 

waters" of the Gila, Ross (1923, p. 66) commented that "by no stretch 

of the imagination could the present day mud-laden water of the Gila 

be considered 'sea green'." Ross was fortunate to see "mud-laden waters;" today the mud has been long laid and the water is only an 

occasional statistic. 

Much of the flood flow over Gillespie Dam in the past 25 years has 

not reached the narrows at Painted Rock. It is assumed that the 

Joss of flow is due to evapotranspiration and to downward percolation, 

but the amount to be attributed to each is not known. Also, it is not 

known how much of the percolation reaches the water table. 

No quantitative comparison of inflow and outflow can be made in the 

Gila Bend area because no long-term records are available from the 

narrows at Painted Rock. However; comparison of the flow records 

at Gillespie Dam with those at Dome, Ariz., about 120 miles downstream from the dam, in the following tabulation gives some measure 

of channel losses in this region and provides a striking contrast between 

the average flows of selected intervals during the periods of record. 

Average annual flow (thousands of acre-feet) 

Station 1901,-$1 19$!e-J,1 191,$-58 19$2-58 

Gillespie Dam ______________ No record___ 325 23 

Dome_____________________ 1,100______ _ _ 200 1. 4 

190 

110 
GROUND WATER, GILA. BEND INDIAN RE,SERVATION A33 

In the Gila Bend area, prehistoric Indians irrigated small acreage 

by diversions from the Gila River. Similar irrigation methods were 

tried inte.rmittently by white settlers in the last half of the 19th century, but ~ere unsuccessful, due largely to the erratic flows of the Gila 

River an<fto a lack of understanding of the problems of farming in the 

area (C. R. Olberg, in Ross, 1923, p. 95-117). Traces of abandoned 

canals are evident in the area. An abandoned pumping station in sec. 

15, T. 5 S.j R. 5 W. identifies the head of the old Papago Canal, which 

was built In 1891 and abandoned sometime after 1923. The irrigation 

canals shown on figures 2 and 4 obtain their water from Gillespie Dam. 

Painted Rock Dam (fig. 2) is currently (1960) being constructed for 

flood-control purposes. Its spillway is planned for an altitude of 660 

feet, or about 40 feet higher than the site of the abandoned pumping 

station. When the water in the reservoir behind the dam is at the 

level of the spillway, the flood plain of the Gila River within the reservation will be inundated. Possible effects of impoundments behind 

the dam are discussed briefly on pages 38 and 42. 

GROUND WA'll'ER 

The water-bearing formations in the Gila Bend Indian Reservation 

area consist chiefly of sand and gravel beds in the older and younger 

alluvial fills. In addition, some water may be obtained from the Sil 

Murk formation. The crystalline rocks are chiefly non-water-bearing 

and are not discussed further. The ground-water body in the older 

and younger alluvial fills is considered to be interconnected with that 

in the Sil Murk formation and the units are discussed together as 

forming a single aquifer-the valley fill. 

V .ALLEY FILL 

The area considered in this report is too small to permit an overall 

estimate of its ground-water resources from data obtained within its 

limits alone. Earlier reports on ground water in the Gila Bend 

region, particularly those by Babcock and others (1948) and Johnson 

and Cahill (1955), have been freely drawn upon for this necessary 

information. 

OCCURRENCE OF GROUND WATER AND SLOPE OF THE WATER TABLE 

All the wells in the area obtain water from permeable units in the 

valley fill. Available data regarding these wells are shown in table 2. 

Depths to water range from about 35 to 60 feet and the slope of the 

water table generally follows the surface slopes. The gradient of the 

surface slope is westward at 10 feet per mile, and the gradient of the 

water table is probably about the same (Johnson and Cahill, 1955, 

pl. 2). 
T.4'W-R.6W. 

S ~S~E~sec.36-L Dr 

SW~SE~E~ sec. 36-2. Dr 

T.5SER.4W. 

S ~SEKNE~ sec. 18 •••• Dr 

SE~SE~SE~ sec. 19.--- Dr 

T.liiJ!wR.liW. ~SEKN"E~ sec.li--L Dr 

N~SEKNE~ sec.li--2. Dr 

SE~EKN"~sec.18 ••• Dr 

NW sw~s sec.18 •• Dr 

SE~SW~SE~ sec. 18 ____ Dr 

NE~SE~SE~ sec. 18 ____ Dr 

SW~SE~SE~ sec. 18-L br 

SW~SE~SE~ sec. 18-2. Tw 

S~8~8E~.sec. UHL Dr .SE SW sec. 22 ___ Dr 

.s sw ~sE s.ec.23 •. c ~r 

NEKN"WKN"W~sec.24. Dr 

SW~SW~SE~sec.24 ••• Dr T.li~R.6W. 

8 w~SW~SE~ sec. L.. Dr 

BE SE~SE~sec.l2 •••• Dr 

SE SE~NE!~ sec.lL.. Dr 

960 24 -------- ------

-------- ------- ........ ;.. ....... -------- ............... ----.---- .... ..;.~.:. .. 

1960 

1951 

501 

926 

20 

20 

0 501 

0 908 

20 -------- ------- -------- ------ --------"-

19M 256 

865 

960 

1957 410 

OliO 

1947 1,031 

1957 800 

1957 708 

1957 1, 44'7 

11157 1,475 

1945 130 

l{,.j7 1,400 

1956 

280 

10 

20 

20 

20 

20 

20 

10 

20 

0 256 C;W 

0 '1131i. . ' __ ;_.-. ~··- ~:_.' 

0 890 ~'P;'J:~"-c 

0 

0 

0 
GOOUND WATER, GILA BEND INDIAN RIDSERVATION A35 

Indfan Reservation and vicinity, Maricopa Oounty, A.riz. 

Water-level depth: Reported depths Indicated by R. 

Rate of discharge: All figures are rounded; reported yields are Indicated by R; estimated yields by E. 

Use: A, abandoned; D, domestic; I, Irrigation; S, stock. 

Supplementary data: x,log or analysis In tables 2 and 3. 

Hydrologic data 

Water level Discharge Altltude 

ofland lise sur- Depth Date Rate Date face (feet) measured (gpm) '-measured 

(feet) 

605 38.03 December 1953. 2,500 April1953 ___ I 

1,600 August 1956 

38.03 _____ do _________ 400 April1953 ___ I 

1,000 August 1956_ 

655 27.07 _____ do _________ 1,400 June 1955 ____ 

705 77.36 _____ do _________ 2,000 April1953 ___ I 

------ -------- ---------------- -------- -------------- A 

610 35.41 December 1954. 30R -------------- s 

630 60R 1948 ___________ -------- -------------- A 

635 55.76 December 1953. 1,000 August 1956_ I 

645 -------- ---------------- -------- -------------- I 

640 51.48 December 1953. 2,800 August 1956_ I 

645 57.22 _____ do _________ 2,900 _ ____ do _______ A 

------ -------- ---------------- -------- -------------- A 

645 

665 

655 

-------- ---------------- -------- -------------- I 

645 33.19 October 1945. _ 

I 

I 

5E -------------- DS 

Supplementary data 

Chemical 

Log analysis of water 

X 

------ --------

X X 

X X 

------ X 

X 

X X 

X X 

X 

X 

X 

------ X 

Remarks 

Yield dropped as pumping rate In well 36-2 Increased. 

About 10 ft west of well 

36-1. Not shown separately on map. 

Drawdown reported 54 ft at 1,400 gpm. Drawdown reported 80 ft at 2,000 gpm. 

About 10 ft north of well 

5-2. Abandoned 1954; not shown separately on map. 

Yield reported from ballIng test. Abandoned 1949. 

Drawdown reported 130 ft at 1,000 gpm. About 100 ft west of well 

18-3. 

Drawdown reported 54 ft at 2,800 gpm. About 50 ft west of well 

18-3. Drawdown re- ported 40ft at 2,900 gpm. 

Abandoned December 

1956; not shown sep- arately on map. 

Test hole reamed out to make well 18-3. Not 

shown separately on map. 

Pilot hole drilled to 1,475 

ft; well reamed out to take 16- and 20-ln. casing to 1ii307 ft. Partial set of we cutting samples available to 1,475 ft, 

Arizona Bureau of Mifles 

Well-Sample Library 

No. 783. Log based on well cuttings only. See figure 14 for hydrograph. 

680 -------- ---------------- -------- -------------- I X 

605 76R ---------------- 2,800 August 1956_ I 

615 --62~35- -A:j)rifi953::::: 2,500 July 1948 ____ I 

625 2,800 April1948 ___ I 

56.90 June 1955 ______ 2,300 August 1956_ 
A36 WATE-R SUPPLY OF INDIAN REISERVATION18-PAPAGO TRIBE 

Earlier reports suggest that ground water moved out of the Gila 

Bend area through the Painted Rock narrows, but water-level 

measurements not available to the earlier writers indicate that at least 

part if not most of the water in the basin moves southwest past Theba 

around the south end of the Painted Rock Mountains (fig. 2). This 

southern area of subsurface outflow has considerable bearing on the 

possible effects of the Painted Rock Dam on water levels in the area, as 

will be discussed under "Fluctuations." 

RECHARGE 

Recharge in the area occurs from four sources : infiltration from flow 

in the Gila River and its tributaries; infiltration from canals and irrigation water applied to the land; underflow of the Gila River; and 

direct precipitation. Infiltration from flow in the Gila River is the 

principal source of recharge to the upper parts of the alluvial aquifers, 

and recharge by infiltration from tributary streams, underflow, and 

direct precipitation is considered to be small or negligible. Some recharge to the Sil Murk formation probably occurs from precipitation 

and runoff on the exposed areas and from runoff where the volcanic 

member forms a partly buried barrier across the present channel of 

the Gila River. Annual recharge from all sources of the Gila Bend 

basin has been estimated to average between 40,000 and 50,000 acrefeet for the years 1947-53 (.Johnson and Cahill, 1955, p. 14-18). 

Recharge within the Gila Bend Indian Reservation, because of the 

small amount of irrigation development along its margins, is probably 

limited and may be no more than enough to replenish evapotranspirative losses. 

DISCHARGE 

Discharge from the Gila Bend basin occurs by evapotranspiration, 

surface flow, underflow, and pumping. Johnson and Cahill (1955, p. 

29) estimate that during 1947-53 a total of about 115,000 acre-feet was 

discharged annually, including about 85,000 acre-feet by pumping. 

Estimates of annual pumpage for irrigation purposes in the Gila Bend 

basin for 1946-56 (U.S. Geological Survey, reference b; Harshbarger 

and others, 1957) are shown graphically in figure 14. 

None of the ground water pumped for irrigation was obtained from 

wells on the reservation proper. The effects of pumping beyond the 

limits of the reservation are discussed under "Storage." 

STORAGE 

The southern and western parts of the Gila Bend Indian Reservation are underlain by as much as about 800 feet of saturated alluvium 

that consists of the younger and older alluvial fills and the coarser units 
::;;: 

::::l 

I-

<( 

0 

w 

u 

;£ 

0:: 

::::l 

(/) 

0 

z 

:5 

3: 

g 

w 

CD 

1-

w 

w 

"-

z 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

70 

75 

80 

_j 8 w 5 

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--' 

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w 

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~ 200 <( 

C/li-

~ 150 

I'7 

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0 

GROUND WATER, GILA BEND INDIAN RESERVATION A37 

1\ 

1\ 

L \ 

I \ / ,/ 

/ I \ / 

Depth to water / 1/ \ V\ - reported in 1948'-y-"' y .-' I \ ll \ 

\ 

\ v 

I SE~ SE~ ~ sec. 11, T. 5 S., R. 6 W. v 

~ ............._ h..._ v ~'----~--- _...-r-.... ....... 1'---- ...... 

Slope based on spring > -..... 

19~0 me sure~ent ......... 

NE~ NW~ NW~ sec. 24, T. 5 S., R. 5 W. 

r---

- Pumpage, Gila Bend area f:77" ':-::. ,,., 1·············•: .••. 

.,, ., .. ,.,.,· 1-·:· ,,,_.,. Estimates of ...........,...,-,___ 

I i,, .. , .. ,.,, ·1

= ·.,,.:•: ... : .. , ... ,,, -~~r~~~~ h:- _Ll U ,_,, .. I'• !····•·'·'·' •:.-···· 

1945 11946 1947 1948 1949 1950 1951 1952 1953 1954 1955 1956 195711958 11959 

FIG URE 14.-Annunl goou ndcwater pumpage in the Gila Bend urea during 1'94,&--56, a nd 

wa ter-l evel flu ctuatiorus lru wells., sec. 24, '1'. 5 S .. , R. 5 W. and sec. 11, T. 5 S., R. 6 W., 

In or near the Gila Bend India n Reservation. 

of the Sil Murk formation. The amount of water that may be 

removed from saturated alluvium in other parts of Arizona is about 

10 to 20 percent of the total volume of the saturated material. The 

amount of available ground wai·er in storage below the Gila Bend 

Indian Reservation down to about 300 feet is estimated conservatively 
A38 WATE,R SUPPLY OF INDIAN REISERVATION!&-PAPAGO TRIBE 

to be about 50,000 to 100,000 acre-feet of water per 100 feet of saturated 

material. Below 300 feet the amount of water in storage is not estimated because the subsurface shape of the contact between the 

alluvium and older rocks and the permeability of the deposits at depth 

are not known. However, this permeability may be assumed to be 

smaller than that of the upper 300 :feet of deposits, and the amount of 

available ground water in storage is assumed to be correspondingly 

smaller. 

The saturated sediments underlying the reservation are interconnected with those below adjacent parts of the ground-water basin. 

There is pumping :for irrigation in the adjacent parts of the basin and 

the effects of this removal of ground water :from storage extend to all 

parts of the basin. The seasonal recharge of the younger alluvium 

along the channel of the Gila River may partly replenish the ground 

water that has been removed :from the adjoining valley fill, but such 

recharge has not been sufficient to offset the losses, as indicated by the 

continuous decline in water levels in wells. 

FL ll'CTU ATIONS 

In the heavily irrigated areas away :from the river, the water table 

in the Gila Bend basin has declined on the average of from 3 to 6 :feet 

per year since 1945. The hydrograph of a well in sec. 11, T. 5 S., R. 

6 W. (fig. 14), immediately west of the area mapped (fig. 4), shows 

a more rapid decline than usual :for the area. Quarterly water-level 

measurements between the winter of 1953 and the spring of 1955 show 

characteristic seasonal fluctuations and graphically demonstrate the 

effects of summer pumpage :for irrigation and recovery during the 

nonpumping seasons. The fluctuations in spring water-level measurements :for 1954-59 show the cumulative effects of pumpage :for irrigation and the seasonal variations in recovery, which in part depend 

on the amount of surface flow in the Gila River. The sharp rise in the 

last hal£ o~ 1954 and the early months of 1955 may be due to heavy 

flow in the Gila River below Gillespie Dam during the late summer 

of 1954. In contrast, a domestic and stock well in an unirrigated part 

of the flood-plain deposits, in sec. 24, T, 5 S., R. 5 W. (fig. 14), showed 

small fluctuations, apparently either in response to fluctuations of 

streamflow in the Gila River alone or in response to a combination 

of streamflow fluctuations and the effects of the general regional 

lowering of the water table. 

Effects of impoundments behind Painted Rock Dam on water levels 

are difficult to evaluate because no data are available re·garding the 

expected :frequency with which water will reach different levels, the 

length of time the water would be allowed to remain in the reservoir, 
TABLE 3.-0hemical analyses of water from selected wells in the vicinity of the GiZa Bend Inairm Reservation, M Olricopa Ooonty, Ariz. 

[Analyses by U.S. Geological Survey; chemical constituents in parts per m1111on] 

Dissolved 

~ ~8- '2 ~ solids 

~ d :::::;- §: 0 'd eo ~ 5 s 

-1~ ~~Gi' .s s ~ "' ~-~~ .. Location Date of ~~ [!3 e il Remarks ~ § El ~ ~ ~§ ~. IIi" 

collection ... Ut .80 .s ,o i "~ ... 

:3 ~ .. .§ ~§ ~ s ·.: 

~ IS i~ l!l~ ... ~0 ~8: 

"" " «< ..~ :a oz :a ~ IS 0 .s f<!t3 ll ~lil.S " "~ ;;:! ~~ 0 10.0 -~~ 

A 8 "' 0 "' ~ "' 0 ~ "" 8 = Po< "' ------------------ -------

T.4S.,R.6W. 

SWUSEUNEU sec. 36 __ Apr. 16,1953 ------ 83 29 116 22 358 150 142 618 3.2 8.8 ---- 1,370 1.86 380 67 2,440 

T. 58., R. 4 W. 

SEUSEUNEU sec. 18 ___ July 3,1953 501 79 24 30 3.5 316 132 100 392 4.0 2.2 ---- 937 1.27 90 88 1,690 Sampled periAug. 22, 1956 

odically. 

Do_----------------- ------ 78 ---- ------ ------ ------ 132 ------ 405 ............. ------ ---- -------- ------ 98 ---- 1, 700 Total iron 0.03 

SEUSEUSEU sec. 19 ___ Apr. 23, 1953 . 926 82 28 65 6.3 423 106 155 600 4.0 1. 7 1.2 1,340 83 2,390 

ppm (1953). 

1.82 188 

T.5S.,R.5W. NW~SWUSEU sec. 18_ Apr. 16, 1953 960 80 35 192 63 767 172 356 1,320 3.1 30 2.0 2,850 3.88 738 69 4,830 

NE ~SEUSEU sec. 18 __ _____ do ________ 550 76 30 242 72 626 219 283 1,240 2.1 40 1.4 2,640 3.59 900 60 4,490 

SW~SEUSEUsec.1s-L Sept. 12, 1950 1,031 77.5 33 160 43 606 234 233 1,020 2.0 20 ---- 2,230 3.03 576 70 3,920 

NE ~NWUNWUsec.24_ Apr. 17, 1953 130 75 26 114 40 268 238 136 484 .6 14 ---- 1,200 ------ 449 56 2,130 Sampled periodlcally. 

Do_----------------- Aug. 22, 1956 ------ 85 25 248 97 368 235 227 980 .4 8.9 ---- 2,070 2.22 1,020 44 3,830 

T. 5 S., R. 6W. SE~SE~SEU sec. 12 ___ Apr. 16, 1953 75 32 210 49 580 183 262 1,080 2.0 19 1.4 2,340 3.18 726 63 4,000 

SE SE r&NEU sec. 13 ___ Apr. 10,1946 230 74 ---- 118 39 565 236 181 915 2.3 5.9 ---- 1,940 2.64 ------ 3,460 Do. 

Do_----------------- Sept. 11, 1952 ------ 76 37 296 90 811 257 399 1,580 1.9 16 ---- 3,360 4.57 ------ 61 5,680 

DO-------"----------- Aug. 23, 1954 ------ 76 38 461 131 1,170 263 619 2,370 1.1 23 ---- 4,940 6. 72 i~260- 60 8,050 

Do_----------------- June 16, 1955 ------ 77 44 304 122 840 257 425 1, 710 1.9 21 ---- 3,590 4.88 59 6,020 
A40 WATER SUPPLY OF INDIAN RESERVATIONlS-PAPAGO TRIBE 

and rates of siltation. In general, howeVer, large and long-standing 

impoundments will tend to raise the water level. Any long-term 

rise in the water table along the Gila River above the dam may create 

a pressure differential that will make the water table slope toward the 

south end of the Painted Rock Mountains. Small temporary 

impoundments, such as would have been produced by the runoff during 

1942-56, probably will have little or no effect on the ground water in 

addition to the normal effects of floodftows. 

QUALITY OF WATER 

The dissolved-solids content of water taken from wells in the older 

and younger alluvial deposits generally ranges from about 1,000 to 

5,000 ppm (parts per million) as shown in table 3. According to U.S. 

Department of Agriculture standards, these waters are classified as 

"doubtful to unsuitable" for irrigation because they contain high concentrations of sodium and boron and relatively high concentrations of 

dissolved solids. Most of the water is hard, has a salty taste, and 

contains more than 1.5 ppm of fluoride, which makes it unsuitable for 

domestic use according to U.S. Public Health Service standards (California State Water Pollution Control Board, 1952, p. 123). 

Surface water that enters the Gila Bend basin during periods of 

low flow sometimes contains more than 5,000 ppm of dissolved solids 

and is high in sodium and chloride. Johnson and Cahill (1955, p. 

35-37) report: 

The period 1942--53 inclusive has been one of drought in most of the Southwest "' "' "' except for the effects of floods of short duration, the flow of the 

river at Gillespie Dam gradually decreased in the period 1944--53. In 1947, 

69,500 acre-feet was diverted into the canals; in 1953 the quantity available for 

diversion was only 22,000 acre-feet. During this same period the waters became 

more highly mineralized. In the water year 1943-44 the weighted average dissolved-solids content was about 3,800 ppm; in the water year 1952-53, about 

5,000 ppm. Except when diluted with floodflows, the surface water diverted into 

the canals "' "' "' is classed as 'unsuitable' for irrigation (Wilcox, 1948). 

Floodflows in the Gila River contain much less dissolved material than low 

flows. The water is of excellent quality in comparison with normal riverflow, 

though it is hard. The following tabulation indicates the difference in dissolvedsolids content between flows greater than 500 cfs (cubic feet per second) and 

flows less than 500 cfs. 

The effect of the quality of the surface water in the Gila River upon the 

quality of the ground-water supply of the Gila Bend area is of great importance. 

For example, by mixing ground water with the surface water diverted into the 

canals, the dissolved-solids content can be reduced sufficiently to make the 

water suitable for irrigation of some crops. Some of this mixture recharges 

the ground-water :reservoir by downward seepage from canals and fields. Some 

leaching of the alluvial materials is likely to occur as this water moves downward to the water table, and the net effect may be to increase the concentration 

of dissolved material in the ground water. 
GROUND WATER, GILA BEND INDIAN RESIDRVATION A41 

Flows greater than 500 cfs Flows less than 500 cfs 

Date 

Mean dis- Dissolved Mean dis- Dissolved 

charge (cfs) solids (ppm) charge (cfs) solids (ppm) 

1951 

July 11-20-------------------- ---------- ---------- 21. 8 5, 450 

July 21-27, Aug. 2------------- ---------- ---------- 29. 9 4, 640 July 28-3L ___________________ ---------- ---------- 457 1, 460 

Aug. 1, 3--------------------- ---------- ------J--- 207 1, 860 

Aug. 4, 5--------------------- 2, 075 487 ---------- ---------- Aug. 6-10--------------------- 734 877 ---------- ---------- Aug. 11-15, 18-26_ _ _ _ __ _ __ _ _ __ __ _ __ __ __ _ _ __ _ _ __ _ _ _ 86. 7 5, 220 

Aug. 16, 17 _ _ _ _ _ _ _ _ __ __ __ _ _ _ _ _ __ _ _ _ __ __ _ _ __ __ _ _ _ _ _ 176 2, 110 

Aug. 21----------------------- 586 881 ---------- ---------- Aug. 28-3L___________________ 8, 500 417 ---------- ---------- Sept. L __ -- _ _ _ __ _ _ _ _ __ __ __ __ _ 4, 640 262 ___________ • -------- Sept. 2 _____________ ----- __ __ _ 2, 540 543 ____________ -- _ ----- Sept. 3, 4_ __ _ _ ___ _ _ _ __ _ __ __ __ _ 507 2, 140 ______________ ------ Sept. 5-10 __________________________________ -• ___ _ 248 5, 660 

Sept. 11-20 __________________________________ ~- __ _ 174 5, 790 

Sept. 21-30_ _ _ _ _ __ _ _ _ _ __ __ _ _ __ __ _ __ __ __ _ _ _ _ __ __ __ _ 100 6, 000 

An important source of recharge of river water in the Gila Bend area is :llood-

:llows. These better quality waters tend to reduce the concentration of dissolved materials in the ground-water supply. 

It is considered likely that a long-term tendency exists for the quality of the 

water supply in the Gila Bend area to deteriorate, at least in the downstream 

part. This tendency exists because more dissolved material is being brought 

into the area than is leaving. 

Surface water is made usable by diluting it with ground water from 

wells. Although the mixed water, as well as the ground water itself, 

is classified as not being particularly suitable for irrigation purposes, 

it continues to be used successfully to raise some salt-tolerant crops 

such as cotton, alfalfa, barley, and sorghum. This is possible partly 

because the water is hard and the high calcium and magnesium contents partly offset the effects of high sodium content. Also, the soil 

in the Gila Bend area is sandy rather than clayey and drains readily; 

therefore, soluble salts tend to be leached rather than accumulated 

(Johnson and Cahill, 1955, p. 38). 

The dissolved-solids content of water from shallow wells, those less 

than 300 feet deep, ranges from about 1,200 to 5,000 ppm. The dissolved-solids content of water from wells deeper than 300 feet ranges 

from about 950 to 2,850 ppm. No significant difference can be discerned at this time between the quality of water from shallow and 

deep wells, but available data do show that the quality of water from 

the . shallow wells fluctuates more than that from deep wells. This 

is because the deep wells are open to receive water from the full thick-
A42 WATER SUPPLY OF INDIAN RESERVATIONS-PAPAGO TRIBE 

ness of penetrated alluvium and the water discharged from them is 

·undoubtedly a mixture of water fro~ many zones. No data are a vailable from the area to determine whether or not there are zones of 

water of preferred quality in the valley fill. Babcock and. others 

(1948, p. 10 and table 2) report that one well about 15 miles west of 

the reservation produced water from 600 feet o£ sandstone which was 

penetrated below a depth of 1,100 feet. The formations above 1,100 

feet were cased off. The dissolved-solids content of water from this 

well was reported to be 1,060 ppm. The chemical quality was, in 

general, similar to that of the water shown in taible 3 of this report, 

except that the calcium, magnesium, and bicarbonate contents were 

proportionally lower and the sodium and potassium combined and 

chloride contents were proportionally higher. The water from this 

well was reported to contain 93 percent sodium, which is somewhat 

higher than the approximate average of 60 percent sodium for the 

wells in table 3 of this report. 

The quality of water in shallow wells in the flood plain of the 

Gila River seems to respond to changes in the flow in the river and 

the amount pumped from the ground-water reservoir. A 130-foot 

well in sec. 24, T. 5 S., R. 5 W., which is pumped for domestic and 

stock purposes only, yielded water that contained 1,200 ppm o:f dissolved solids in 1953 and about 2,000 ppm in 1956. The dissolved 

solids in a 280-foot irrigation well in sec. 13, T. 5 S., R. 6 W., however, 

increased :from about 2,000 ppm in 1946 to nearly 5,000 ·ppm in 1954 

and then decreased to about 3,600 ppm in 1955. The changes in dissolved-solids content are apparently related to flow in the river because 

1952 and 1953 were years of almost no flow past Gillespie Dam, and 

1954 and 1955 were years of above-average flow. 

Impoundment of large quantities o:f flood water of comparatively 

low dissolved-solids content behind Painted Rock Dam may result in 

small temporary decreases in the dissolved-solids content of ground 

water in the younger alluvium. On the other hand, impoundment of 

water in quantities similar to the level of runoff during 1942-58 will 

have almost no effect. 

AVAILABILITY OF GROUND WATER FOR FUTURE DEVELOPMENT 

The Bureau o:f Indian Affairs estimates that within the Gila Bend 

Indian Reservation, about 1,200 acres, in addition to about 375 acres 

under cultivation in 1955, is arable. The annual publication of the 

University of Arizona Agricultural Exper~ment Station entitled, 

"Arizona Agriculture" gives consumptive-use figures by crops. These 

figures range from about 2% to 51;2 acre-feet per acre. In general, 
GRIOUND WATER, GILA BEND INDIAN REISE·RVATION A43 

it is estimated that about 4 acre-feet of water is needed to irrigate 

crops in southern Arizona. The amount of water needed to irrigate 

the 1,200 acres is estimated to be about 5,000 acre-feet per year. 

It is assumed that the 5,000 acre-feet needed to irrigate the 1,200 

acres will be obtained from ground-water sources underlying the 

Gila Bend Indian Reservation. These sources have been estimated 

conservatively to contain between 50,000 and 100,000 acre-feet of 

available water per 100 feet of saturated material to a depth of about 

300 feet. Below 300 feet the amount of available ground water in storage per 100 feet of saturated thickness is presumed to be smaller. 

Depths to water range from about 35 to 60 feet and water levels in 

heavily irrigated areas in the Gila Bend basin have declined on the 

average from 3 to 6 feet per year. For the purposes of this discussion, 

the average depth to water in the reservation is assumed to be a.bout 50 

feet in 1960 and the average decline, when the 1,200 acres are irrigated 

will be about 5 feet per year. During an assumed 25-year period of 

irrigation the water table therefore would be expected to be lowered 

about 125 feet, to a total depth of 175 feet. During this 25-year 

period the median depth to water, rounded to the nearest 10 feet, would 

be about 90 feet. The median thickness of saturated material above 

the 300-foot level for this period, therefore, would be about 210 feet, 

and would contain about 100,000 to 200,000 acre-feet of available 

water. 

These calculations ignore the possible changes in the rates of recharge and withdrawal that result principally from fluctuations in the 

amount of annual flow in the Gila River and ground-water pumpage 

for irrigation in the Gila Bend basin. Nonetheless, it !leems conservative to assume that there is sufficient ground water in storage 

in the upper 300 feet of alluvial deposits beneath the Gila Bend India.n 

Reservation to irrigate 1,200 acres for at least 25 years. 

The chemical quality of water available from the upper 300 feet 

of alluvium apparently changes in response to large withdrawals 

from storage and fluctuations in the amount of flow in the Gila River. 

For the period of record, these changes in general have been deleterious. It must be anticipated that, unless the period of increased 

withdrawals corresponds with a period of large runoff of low dissolved-mineral content in the Gila River, the quality of water above 

the 300-foot le.vel will deteriorate. Data are insufficient to determine 

the effects on chemical quality of long-term pumping of the water 

from below 300 feet. 
A44 WATE·R SUPPLY OF INDIAN REISERVATIONS-PAPAGO TRIBE 

SUMMARY AND CONCLUSIONS 

1. The principal aquifer in the area is the valley fill, which comprises the hydrologically interconnected younger and older alluvial 

fills and the coarser fraction of the Sil Murk formation. The saturated thickness of the valley fill under the reservation ranges from 

about 800 to more than 1,400 feet and yields of wells are adequate for 

irrigation purposes. 

2. In the mountain and foothill areas, ground-water supplies in 

quantities sufficient for domestic purposes may be obtained locally in 

the Sil Murk formation and in the crystalline rocks. 

3. Depths to water under the Gila River flood plain and the Gila 

Bend plain range from about 35 •to 60 feet. The water table in nonirrigated areas along the Gila River shows only small declines and 

fluctuates either in response to streamflow in the Gila River alone or 

in combination with the regional lowering of the water table. 

4. Pumpage for irrigation purposes in the. surrounding Gila Bend 

basin increased from about 30,000 to 180,000 acre-feet per year in 

1946-56. The water table in irrigated areas declined at about 3 to 6 

feet per year during the same period. 

5. Annual recharge from all sources for the Gila Bend basin is 

estimated to average between 40,000 and 50,000 acre-feet for 1947-53. 

Recharge within the Gila Bend Indian Reservation is estimated to be 

limited to an amount sufficient to replenish evapotranspirative losses. 

6. Surface flow in the Gila River is regulated by upstream storage 

and diversions and the riverbed is dry except during peak floods. 

7. Water levels under the reservation, even without further irrigation development within its boundaries, may be expected to decline 

eventually because of ground-water use elsewhere in the basin and 

upstream appropriation of surface water. 

8. Ground water in storage beneath the Gila Bend Indian Reservation is sufficient to irrigate the 1,200 acres of arable land not under 

cultivation at this time for at least 25 years. 

9. Although the chemical quality of water is not considered by 

accepted standards to be particularly suitable for irrigation, the 

water continues to be used successfully to raise salt-tolerant crops. 

10. The temporary impoundment of water behind the Painted 

Rock Dam may increase recharge and raise the water table, particularly following large impoundments held for long periods. 

11. Impoundment of flood water and recharge behind Painted 

Rock Dam may result in a small temporary decrease in the dissolvedsolids content of ground water in the younger alluvial fill. 

12. Impoundment of floodwater in quantities similar to the flows 

of 1942-58 will result in little or no effect on ground water under the 

reservation. 
GROUND WATER, GILA BEND INDIAN RE,SERVATION A45 

REFERENCES CITED 

Babcock, H. M., Kendall, K. K., and Hem, J. D., 1948, Geology and groundwater resources of the Gila Bend basin, Maricopa County, Arizona: U.S. 

Geol. Survey open-file rept. 

California State Water Pollution Control Board, 1952, Water quality criteria: 

Pub. 3, 511 p. 

Fenneman, N. M., 1931, Physiography of western United States: New York, 

McGraw-Hill Book Co. 534 p. 

Gazin, C. L., 1942, The late Cenozoic vertebrate faunas from the San Pedro 

Valley, Arizona: U.S. Natl. Mus. Proc., v. 92, no. 3155, p. 475-518. 

Gilluly, James, 1946, The Ajo mining district, Arizona: U.S. Geol. Survey Prof. 

Paper 209. 

Harshbarger, J. W., and others, 1957, Annual report on ground water in Arizona, 

spring 1956 to spring 1957: Arizona State Land Dept., Water Resources 

Rept. 2, 42 p. 

Johnson, P. W., and Cahill, J. M., 1955, Ground-water resources and geology of 

the Gila Bend and Dendora areas, Maricopa County, Arizona: U.S. Geol. 

Survey open-file rept., 53 p. 

Lance, J. F., 1960, Stratigraphic and structural position of Cenozoic fossil localities in Arizona: Arizona Geol. Soc. Digest, v. 3, p. 155-160. 

McClymonds, N. E., 1959, Precambrian and Paleozoic sedimentary rocks on the 

Papago Indian Reservation, Arizona : Arizona Geol. Soc., Southern Arizona 

Guidebook 2, p. 77-84. 

McKee, E. D., 1947, Paleozoic seaways in western Arizona: Am. Assoc. Petroleum 

Geologists Bull., v. 31, p. 282-292. 

Ross, C. P., 1922, Geology of the lower Gila region, Arizona: U.S. Geol. Survey 

Prof. Paper 129-H. 

---1923, The lower Gila region, Arizona, a geographic, geologlc, and hydrologic reconnaissance with a guide to desert watering places: U.S. Geol. 

Survey Water-Supply Paper 498. 

U.S. Geological Survey (a), Surface-water supply of the United States, pt. 9, 

Colorado River basin: U.S. Geol. Survey Water-Supply Papers. (Issued 

annually.) 

--- (b), Water levels and artesian pressures in observation wells in the 

United States, pt. 6, Southwestern States and the Hawaiian Islands: U.S. 

Geol. Survey Water-Supply Papers. (Issued annually.) 

University of Arizona, Arizona agriculture: Agricultural Expt. Station, Univ. 

Arizona, Tucson. (Issued annually.) 

Wilcox, L. V., 1948, Explanation and interpretation of analyses of irrigation 

waters: U.S. Dept. Agr. Circ. 784. 

Wilson, E. D., 1933, Geology and mineral deposits of southern Yuma County, 

Arizona: Arizona Bur. Mines Bull. 134. 

Wilson, E. D., and Moore, R. T., 1959, Structure of Basin and Range province 

in Arizona: Arizona Geol. Soc., Southern Arizona Guidebook 2, p. 89-106. 

Wilson, E. D., and others, 1957, Geologic map of Maricopa County, Arizona : 

Arizona Bur. Mines. 

---1959, Geologic map of Pinal County, Arizona: Arizona Bur. Mines. 

INDEX 

Page Page 

Alluvium, age ______________ -----_-----_______ A22 Location of area _____ ----- __ --_-- __ ---- __ -_--- A2 

older fill---------------------------- 22, 23, 27,30 Locomotive fanglomerate _____________________ 19,20 

yield __________ . __________________________ 22, ~3 

younger deposits_. ___ -----------· ________ 23,31 Mesozoic sedimentary rocks ______________ 6, 7, 29,30 

Altitude ___ ----· ------------------------------ 4 Outcrops, hard-rock ___ ----------------------- 2 Aquifers ______________________________________ 22• 33 Sil Murk formation ____________________ 10, 11,15 

Babcock, H. M,, quoted ______________________ 27,31 

Batamote andesite____________________________ 20 

Bibliographic references, chronologie__________ 4, 5 

Block diagram________________________________ 28 

Cahill, J. M., and Johnson, P. W., quoted___ 39 

Channel deposits_____________________________ 4, 23 

Chemical analyses of water from selected wells_ 39 

Climate______________________________________ 4 

Conclusions _______________________ .__________ 44 

Consumptive use of water-------------------- 42-43 

Crystalline rocks_____________________________ 7, 30 

Crystalline rocks, correlation oL______________ 7 

water-bearing characteristics______________ 7, 33 

volcanic rocks_--------------------------- 15 

Painted Rock Dam, effect on dissolved-solids 

content In ground water__________ 42 

effect on water level in area.-------------- 36,38 

location-_----------------_--------------- 2 

spillway altitude __ ----------------------- 33 

Paleozoic sedimentary rocks ______________ 6, 7, 29,30 

Papago Canal________________________________ 33 

Papago Indian Reservation___________________ 2, 3 

Papago Indians, cens.J.s_______________________ 4 economy ________________________________ _ 4 

Precambrian sedimentary rocks _____________ 6, 7,29 

Previous investigations----------------------·· 4, 5 

Quality of water, analyses____________________ 40 

Discharge_ _ __ ------- _ ----------------------- 36 classlllcation ____________ ---- __ -- _ --------- 39 

response to change in flow in Gila River__ 42 

Fanglomerate unit of Babcock and others suitability for irrigation ___________________ 39,41 

(1948) _____ -. ---------------------- 19 Quaternary deposits---------------·· ____ 21-23,30, 31 

Flood-plain deposits, description ___ ._--------

geology oL ____________ ------------- _ --- __ 

4,23 

6 Recharge_-------------- ... -------------------- 36 

Fluctuations in water-level measurements ___ _ 38 References cited _____ -- _______ ---. _ --- -------- 45 

Geologic history ___________________ --- ________ 29--31 

map______________________________________ 9 

sections ___________________________________ 16, 28 

Gila Bend Indian Reservation, geology oL _ _ _ 4, 6, 9 

Gila Bend Motmtains fault block _____________ 21,29 

Gila Bend Mountains, geology of_ _______ 7, 10, 29,30 

Gila Bend plain, geology of_ ____ 6,15, 21, 22, 23, 30,31 

Gila River, annual flow, Dome, Ariz___ ______ 32 

annualllow, Gillespie Dam_______________ 32 

area drained bY--------------------------- 4 recharge along channel oL ________________ 38,39 

Gillespie Dam-------------------------------- 32,38 

Ground water, availability _____________ 33, 37, 42-43 

future development _______________________ 42-43 

pumpage_ -------- __ ---------------------- 37 

movement________________________________ 36 

occurrence ____________________ ---- ___ ----- 33 

supplies _______________________ -~ _________ 36-38 

yield _______________________________ 14, 15, 22, 23 

Irrigation __________________________________ 32, 33,38 

Sil Murk formation, age _______________ 6, 7, 19, 20,21 

arkosic sandstone of______________________ 12 

conglomerate facies of -------------------- 11,13 

correlation with Locomotive fanglomerate_ 19 

eolian sandstone of. __ -----------------·-- 16 

facies of sedimentary member __________ 11,12, 27 

fanglomerate of_ __________________________ 11,13 

faults in ___ ---_--- ______ ------------------ 30 

ground-water yield ___ -------------------- 14, 15 

lithologic characteristics __ -------------·-- 10, 11 origin _____________________ --------------- 19, 20 

sandstone facies ___________ --------------- 11, 30 

sedimentary member oL _________________ 11-15 

facies. __________________ -- ___ ------ 11, 12, 27 

thickness ___________ ------------------ 11,14 

thickness _________ -- ___ ---- __ --- __ -------- 7, 11 

topographic features______________________ 10 

volcanic member of_ _____ ------------ __ 11, 15-19 

lithologic characteristics ___________ 15,16,18 

stratigraphic sections _________________ 18,19 

water-bearing characteristics ___________ 14-15,19 

Slope of water table __ ------------------··----- 33,36 

Storage ____________________ --- _______ --_------ 36, 37 

Johnson, P. W., and Cahill, J. M., quoted_._ 39 Stratigraphic sections _________________________ 18, 19 

Stratigraphic variations, volcanic member of 

Kendall, K. K., quoted ___ , ___________________ 27,31 Sil Murk formation _____________ _ 16 

A47 
A48 INDE~ 

Page 

Stratigraphy, adjacent areas------------------ A 7 

Gila Bend plain__________________________ 6, 23 

subsurface ________________________________ 23, '0 

Stmcture, age of faulting_____________________ 20 

regional relations ______ ~-----·---·-------- '0-29 

S1llllll13rY-••• -----· -------------------------- 44 

Surface water, annual ftow _ ------------------ 32 

quality of.------------------------------- 39-41 

Terraces ____________________________ ---------- 21,22 

Tertiary deposits, adjacent areas_____________ 7 

lithologic description ____________ 20, 21, 22, 30,31 

Topographic features------------------------- 6,10 

Page 

Valley ftll, aqulfer In------------------------- A33 

tblckness _______________ ------------------ 44 

Water resources •. ---------------------------- 31-43 

Wells, chemical analyses of water from selected. 40 

depth of-----------------------·-------- 6, 15,23 description of selected ____________________ 34,35 

drillers' logs of------------------------- 23,24--26 

location of-----------------------·-----... 8 

yield of water __ ----------------------- 15,23, 35 

Yield of water _____________________________ 16, 23,43 

0