Water Resources of 

Lower Colorado RiverSalton Sea Area as of 1971, 

Summary Report

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-A

Water Resources of 

Lower Colorado RiverSalton Sea Area as of 1971, 

Summary Report

By C. C. MC DONALD and 0. J. LOELTZ

WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-A

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1976
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary

GEOLOGICAL SURVEY

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

McDonald, Charles Casto.

Water resources of lower Colorado River-Salton Sea area as of 1971.

(Water resources of lower Colorado River-Salton Sea area) (Geological Survey Professional Paper 486-A)

Bibliography: p.

Supt. of Docs. No.: I 19.16:486-A

1. Hydrology-Arizona. 2. Hydrology-California Salton Sea region. 3. Water-supply-Arizona. 4. Water-supply CaliforniaSalton Sea region. 

I. Loeltz, Omar Joseph, 1914- joint author. II. Title. III. Series. IV. Series: United States Geological Survey Professional

Paper 486-A. 

QE75.P9 No. 486-A [GB705.A6] 557.3'08s [553'.7r 0979499] 75-619440

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

Washington, B.C. 20402 

Stock Number 024-001-02824-7
CONTENTS

Page Page

Conversion factors .................................... IV Summary of results Continued

Abstract ............................................. Al Geology Continued

Introduction.......................................... \ Rock units and occurrence of ground water ...... A21

Demands for water, accompanying problems, Needles and Parker-Blythe-Cibola areas .... 21

and resulting legislation.......................... 2 Yuma area............................... 21

Purpose and scope................................. 7 Imperial Valley area ...................... 22

Project history.................................... 7 Chemical quality of ground water................... 23

Acknowledgments ................................ g Hydraulic properties of rocks....................... 24

Summary of results.................................... g Ground-water resources........................... 24

Magnitude and distribution of the water supply ....... g Virgin conditions............................. 24

Water loss ....................................... \Q Conditions during development ................ 26

Consumptive-use rates............................. n Ground-water movement.................. 28

Water budgets.................................... 12 Changes in the hydrologic environment.................. 28

Chemical quality of the Colorado River ............... 13 Continuing problems and proposed investigations ......... 33

Geology.......................................... 15 Selected references.................................... 34

Landforms ................................... 15

ILLUSTRATIONS

Page

F IGURE 1. Index map of the Colorado River and Salton Sea basins showing project area .................................... A3

2, 3. Map showing principal features of the Colorado River System and areas of water use:

2. Between Davis Dam and the south end of Cibola Valley ................................................ 4

3. Below Cibola Valley ............................................................................... 5

4. Map showing principal features of the Colorado River distribution system and areas of water use in the Salton Sea

basin.............................................................................................. 6

5. Schematic diagram showing distribution of Colorado River water below Davis Dam, 1961-63 ..................... 9

6. Graphs showing depletions of streamflow between Davis Dam and Imperial Dam............................... 14

7-10. Maps showing land forms in the project subareas:

7. Needles area ..................................................................................... 17

8. Parker-Blythe-Cibola area ......................................................................... 18

9. Yuma area ....................................................................................... 19

10. Imperial Valley area............................................................................... 20

11. Map showing transmissivity values for the younger and older alluviums in the Yuma area...................... 25

12-16. Map showing:

12. Change in water level beneath Yuma Mesa, 1925-66 ................................................... 27

13. Generalized water-level contours during 1962-69 in Mohave Valley ...................................... 29

14. Generalized water-level contours in Parker-Blythe-Cibola area, 1964 .................................... 30

15. Average water-level contours in the delta region in December 1965...................................... 31

16. Water-level contours of main body of ground water in Imperial Valley, 1965 .............................. 32

TABLES

Page

TABLE 1. Average annual flow in the lower Colorado River system, 1961-63 ................................................ A10

2. Consumptive use of water between Davis Dam and Imperial Dam ................................................ 13

3. Consumptive use of water in Yuma area, 1951-66............................................................... 13

4. Annual weighted-average chemical analyses for Colorado River below Hoover Dam, Ariz.-Nev..................... 15

5. Annual weighted-average chemical analyses for Colorado River at Imperial Dam, Ariz.-Calif....................... 16

in
IV CONTENTS

CONVERSION FACTORS

[Factors for converting the English units used in this report to metric units are listed below]

Acres................................. 4.047 x 10' 3 Square kilometres (km2).

Acre-feet (acre-ft)...................... 1.233 x 10' 3 Cubic hectometres (hm3).

Acre-feet per year (acre-ft/yr)........... 1.233 x 103 Cubic metres per year (m3/yr).

Cubic feet per second (ft3 /s)............. 2.832 x 10' 2 Cubic metres per second (m3/s).

Feet (ft)............................... 3.048 < 10' 1 Metres (m).

Feet per mile (ft/mi).................... 1.894 x 10-1 Metres per kilometre (m/km).

Gallons per day per foot [(gal/d)/ft] ..... 12.42 Litres per day per metre [(l/d)/m].

Gallons per day per square foot [(gal/d)/ft2 ]40.75 Litres per day per square metre [(1/d) /m2]

Gallons per minute (gal/min)............. 6.308 x 10'2 Litres per second (1/s).

Gallons per minute per foot [(gal/min)/ft].. 2.070 x 10" 1 Litres per second per metre [(l/s)/m].

Inches (in.)............................ 2.54 xlO' 2 Metres (m).

Miles (mi)............................. 1.609 Kilometres (km).

Square feet (ft2 )........................ 9.290X10' 2 Square metres (m2 ).
WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA

AREA, SUMMARY REPORT AS OF 1971

By C. C. MC DONALD and 0. J. LOELTZ

ABSTRACT

Distribution of the available supply of Colorado River water in an 

equitable manner to all parties dependent on that water will always 

pose problems. In recent years, a regional approach is being taken 

in seeking a solution to these problems.

Unless the ever-increasing demands on Colorado River water are 

curtailed, the demands will exceed the dependable supply before 

the end of the 20th century. The net supply of Colorado River 

water below Davis Dam for normal runoff conditions is estimated 

at 10.2 million acre-feet for 1975 and 8.4 million acre-feet for the 

year 2030. For dry conditions, the corresponding supplies are 8.2 

million and 6.4 million acre-feet, respectively. The present basic 

allotment to Arizona, California, and Mexico is 8.7 million acre-feet 

per year, to which is added conveyance and storage losses 

averaging 900,000 acre-feet per year, making the total 9.6 million 

acre-feet of water per year. The supply probably will be adequate 

during periods of near-normal runoff until about 1980.

The river, either directly or indirectly, is the principal source of 

the ground-water supply. Large yields commonly are obtainable 

from wells that tap coarse Colorado River deposits. Evaporation 

from the river and from reservoirs consumes more than 1 million 

acre-feet of water per year. Riparian vegetation consumes more 

than 500,000 acre-feet of water per year. About 1.3 million 

acre-feet per year drains to the Salton Sea, where it evaporates. 

Normal annual evaporation from the sea is 69 inches.

Dissolved-solids concentration of the river water increases with 

distance downstream and with time. For 1951-55 the dissolvedsolids concentration below Hoover Dam averaged 658 milligrams 

per litre, and at Imperial Dam, 706 milligrams per litre. For 

1961-65 the concentration was 714 and 824 milligrams per litre, 

respectively.

The earth materials of the lower Colorado River-Salton Sea area 

comprise a basement complex of pre-Tertiary crystalline rocks, an 

overlying sequence of slightly to moderately deformed 

sedimentary and volcanic rocks of Tertiary age, and the virtually 

undeformed alluvial and windblown deposits of late Tertiary and 

Quaternary age, which were deposited after the Colorado River 

entered the area.

The alluvial deposits constitute the upper principal part of the 

ground-water reservoir. Beds of coarse sand and gravel, deposited 

chiefly by the Colorado River, yield copious quantities of water to 

irrigation and other large wells. Ground water in the valleys is 

derived almost wholly from the Colorado River, except in the Yuma 

area where a significant part was derived from the Gila River.

Sulfate reduction appears to be a major process in the chemical 

alteration of river water to ground water that contains fewer 

dissolved solids than river water. Fresh water (less than 1,800 

mg/1 dissolved solids) extends to depth of more than 2,500 feet in 

the south-central and southwestern parts of the Yuma area. 

Beneath most areas in central Imperial Valley, ground water

contains sufficient dissolved solids to make it unsatisfactory as a 

domestic or an irrigation supply.

Westward movement of ground water to Mexico in 1960-63 was 

about 33,000 acre-feet per year; southward movement east of the 

river was about 35,000 acre-feet per year. A large part of the 

leakage from the All-American Canal in the 37-mile reach west of 

Pilot Knob, estimated at 150,000 acre-feet annually in 1961-63, 

moves southward across the international boundary to Mexicali 

Valley.

Pumpage from drainage wells, sumps, and drains adjacent to 

Yuma Mesa increased from about 70,000 acre-feet in 1960 to 

146,000 acre-feet in 1969. This increased drainage added to the 

problem of satisfactorily disposing of 200,000 acre-feet per year of 

moderately saline (4,000-6,000 mg/1) pumped return flow from the 

Wellton-Mohawk area.

INTRODUCTION

The annual flow of the lower Colorado River of 

about 9 million acre-feet is vital to the economic 

well-being of millions of people in Arizona, California, 

Nevada, and northern Mexico. The river furnishes 

four-fifths of the water that has changed much of 

southern California from a barren desert to one of the 

most productive agricultural areas and to the largest 

and fastest growing industrial and municipal area in 

the United States. More than half a million acres in 

Imperial and Coachella Valleys alone is irrigated with 

Colorado River water. Billions of kilowatt-hours a 

year of electricity is generated with Colorado River 

water. Millions of people in more than 100 cities in 

southern California receive Colorado River water 

through the Colorado River aqueduct, which heads at 

Parker Dam on the main stem of the river 250 miles to 

the east. The river also is virtually the sole source of 

water for the arid lands of western Arizona. Several 

hundred thousand acres in Arizona and California 

along the main stem of the river is irrigated with river 

water. The arid region of southern Nevada is 

dependent on the river for water that will be needed 

for further substantial development of that part of the 

State. Mexico, too, depends heavily on the Colorado 

River for a large irrigation development in the 

Mexicali Valley of Baja California and Sonora, Mexico.

Al
A2 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

In recognizing that the extensive uses of Colorado 

River water and the increasing demands for water 

might cause the total demands to exceed the available 

supply, the U.S. Geological Survey was prompted in 

1960 to undertake a comprehensive study of the water 

resources of the lower Colorado River-Salton Sea 

area. The study, known as the lower Colorado River 

project, was similar to an earlier investigation made 

by the U.S. Geological Survey of the water resources 

of the upper Colorado River (lorns and others, 1965). 

A summary of the lower Colorado River project and of 

the resulting findings is the subject of the present 

report.

The lower Colorado River Project includes most of 

the areas for which the lower Colorado River is the 

principal source of water supply. As defined by 

drainage boundaries, the project area consists of the 

Salton Sea drainage basin and the natural drainage 

basin of the Colorado River below Davis Dam, 

Ariz.-Nev., excluding the Bill Williams River basin 

above the gaging station near Alamo, Ariz., and the 

Gila River basin above the Wellton-Mohawk Irrigation 

and Drainage District. To facilitate the investigations 

and the reporting thereon, the project area was 

divided into subareas, the principal ones of which are 

designated the Needles area, the Parker-BlytheCibola area, the Yuma area, and the Imperial Valley 

area.

Limited studies of areas in Mexico were made in 

collaboration with the Mexican Government only 

insofar as necessary to delineate the hydrologic 

problems and the relations of the various components 

affecting the water resources near the international 

boundary. The relation of the project area to the 

entire Colorado River basin is shown in figure 1. The 

major features of the Colorado River system and the 

principal places of use of Colorado River water in the 

project area are shown in figures 2-4.

DEMANDS FOR WATER, ACCOMPANYING 

PROBLEMS, AND RESULTING LEGISLATION

Because most of the project area is arid to semiarid, 

attempts to divert river water for agriculture date 

back to the earliest settlement. However, the wide 

annual fluctuations of river stage, discharge, and silt 

load carried by the river caused most early attempts 

to divert water to be short-lived, and all diversion 

works were expensive to maintain and were only 

partly satisfactory.

California led the States of the lower basin in the 

early and expanding use of Colorado River water.

However, this early development of the river water 

and plans for further development did not go 

unnoticed by the other States of the Colorado River 

basin. Consequently, by agreement among the States, 

in what is known as the Colorado River Compact of 

1922, the water of the Colorado River was apportioned 

between the upper basin States (Colorado, New 

Mexico, Utah, and Wyoming) and the lower basin 

States (Arizona, California, and Nevada) on the basis 

that each group was to have the exclusive beneficial 

consumptive use of 7.5 million acre-feet of water per 

year.

Six years later, in 1928, Congress adopted the 

Boulder Canyon Project Act authorizing construction 

of Hoover Dam and powerplant and of the 

All-American Canal to Imperial and Coachella Valleys. 

Demands for river water increased rapidly with the 

building of Hoover Dam and other main-stream dams 

which controlled the annual floods, thereby permitting 

orderly and reliable diversions.

The rapid development of uses of Colorado River 

water in the United States caused concern in Mexico 

about the continued availability of Colorado River 

water for irrigation in Mexico. About 1940 Mexico 

began negotiations with the United States leading to a 

recognition of Mexican rights to water from the 

Colorado River and the Rio Grande. As a result of 

these negotiations, the Rio Grande, Colorado, and 

Tijuana Treaty was signed in 1944 and ratified in 1945. 

Under terms of the treaty Mexico is guaranteed 1.5 

million acre-feet of Colorado River water annually. 

The treaty guarantee is a first lien on the flow of the 

river and therefore limits the availability of water in 

the United States for meeting growing demands.

Although the Boulder Canyon Project Act of 1928 

authorized a compact to divide the lower basin's share 

of the Colorado River water among Arizona, California 

and Nevada, the States were not able to agree as to 

their respective shares. Finally, in 1952 Arizona filed a 

suit in the Supreme Court of the United States (known 

familiarly as Arizona v. California et al) seeking to 

establish its right to river water. The Supreme Court, 

on March 9, 1964, decreed that of the first 7.5 million 

acre-feet per year available in the main stream for use 

in the three lower basin States, Arizona was to receive 

2.8 million acre-feet; California, 4.4 million acre-feet; 

and Nevada, 300,000 acre-feet; and that any flow 

available for such use in excess of 7.5 million acre-feet 

was to be divided equally between Arizona and 

California, except that Nevada was entitled to 4 percent of the excess, which was to come from Arizona's 

share. The apportionment of flows in years when such 

flows would be less than 7.5 million acre-feet is to be 

determined by the Secretary of the Interior in
119°

SUMMARY REPORT AS OF 1971

114° 109°

A3

42° -

37° rEXPLANATION GREAT 

I SALT 

\ LAKE

Lower Colorado River 

Salton Sea area

LX O 

SALT LAKE CITY ver ixnoraao nn 

Salton Sea area

Drainage-basin boundary

Compact point/\. . . _

/-Marble Canyon 

 damsite

Grand' 

Canyon

ridge Canyon damsite

oLos Angeles -..,

I/ 

I UNITED STATES^El Paso

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1 I

\ U- "r .-: i-r J

SONORA

GULF OF I 0 50 100 MILES 

CALIFORNIA I , ;/ i <

0 50 100 KILOMETRES V

FIGURE L Index map of the Colorado River and Salton Sea drainage basins, showing the project area.
A4 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

115° 114

LAKE MOHAVE EXPLANATION

Drainage-basin boundary

1 1 1 1 1 1 1 1 1 1 1 1 i i M 1 1 1 M 1 1

Approximate boundary

of water-using area

FORT HOHAVE

RESERVATION

MOHAVEA II 

VALLEY -M

\

LAKE HAVASU

Lake Havasu City CHEMEHUEVI 

INDIAN RESERVATION

COLORADO RIVER 

r-INDIAN RESERVATION o Metropolitan 

Water District 

of Southern 

California

VERDE VALLEY

KOFA(MTS

20 MILES

1 I I

10 20 KILOMETRES

FIGURE 2. Principal features of the Colorado River system and areas of water use between Davis Dam and the south end of Cibola Valley.
SUMMARY REPORT AS OF 1971 A5

115°00' 114° 30' 114°00' 113°30'

\

/IMPERIAL WILDLIFE 

 -f REFUGE BOUNDARY

33° 

00'

EXPLANATION

Drainage-basin boundary

111111111111 i i 1111 i 111111

Approximate boundary

of water-using area

S ALTON SEA " 

BASIN

Senator Wash'< 

Reservoir

'YUMA INDIAN RESERV

 Imperial Dam

ILA GRAVITY MAIN CANAL

;una Dam 

'YUMA MAIN V\' ' ' rT>X><v/ t*

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11111111111

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vv pumping plant

WELL TON-MOHA WK CANAlS

32' 

30'

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10

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I 

20 KILOMETRES

20 MILES

I

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FIGURE 3. Principal features of the Colorado River system and areas of water use below Cibola Valley.

accordance with broad outlines set forth in the Decree 

and in the Colorado River Basin Project Act (Public 

Law 90-537, September 30, 1968). (See p. A33 for 

major features of the act).

Of principal concern to California and Arizona is the 

apparent inadequacy of the Colorado River to meet 

their growing demands for water. On the basis of the 

projects completed and those authorized there is little 

doubt among the lower basin States that the water

supply of the lower Colorado River system is 

overcommitted.

In addition to the problem of an inadequate supply, 

there are also problems of conflicts of interest 

concerning utilization of the available supply. 

Demands for water include not only municipal, 

irrigation, and electrical-power-generation demands, 

but also, in recent years, a mushrooming recreational 

demand. Conflicts of interest among these diverse
WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

116° 115°

Drainage-basin boundary

I I I I I I M I I I I M I I I I I I I I I I

WestmorlandQ

\ 4f6Brawley 

VI PERI AL

0 10 20 30 KILOMETRES

33 C

FIGURE 4. Principal features of the Colorado River distribution system and areas of water use in the Salton Sea basin.

demands are almost inevitable. River management, a 

responsibility of the U.S. Bureau of Reclamation, 

therefore becomes increasingly difficult.

In addition to problems of water quantity are the 

problems of water quality. Of particular concern to the 

irrigation communities is the salinity of the water. In 

the lower Colorado River, salinity has already reached 

sufficient concentration that a substantial part of the 

irrigation water must be used to wash excess 

concentrations of salt from the root zones of crops. As 

more water is used consumptively in the upper basin

States, the concentration of salts in the remaining 

water available to the lower reaches will increase. The 

rate at which the chemical quality will deteriorate and 

the effect of such deterioration on the economy of the 

lower basin States is of great concern to them.

Deteriorating water quality also has created 

international concern. A problem of this nature arose 

in 1962 when about 300 ft 3 /s of saline ground water 

pumped from drainage wells was discharged into the 

Gila River near its confluence with the Colorado 

River. The Mexican Government and water users in
SUMMARY REPORT AS OF 1971 A7

the United States downstream from the points where 

the water entered the Colorado River protested the 

action. As a result of negotiations with Mexico, the 

United States agreed to construct a bypass 

conveyance channel that would permit any part or all 

of the saline drainage water to be discharged into the 

Colorado River below Morelos Dam, the point of 

diversion for most of the water delivered to Mexico. 

This arrangement was recognized as only a temporary 

solution to the problem. The Minute under which the 

operation was conducted was to be in effect for a 

period of 5 years following the date of completion and 

placing in operation of the conveyance channel, which 

occurred on November 16, 1965. In November 1970 

and 1971 the Minute was extended for an additional 

year while both parties continued working for a 

permanent and effective solution.

PURPOSE AND SCOPE

The general purpose of the lower Colorado River 

project study was to determine the quantity and 

extent of the various components of the total water 

resources of the lower basin and the relations among 

the various components in order to provide a better 

basis for the efficient and satisfactory management of 

the available water.

The study consisted of an evaluation of the quantity 

and quality of surface- and ground-water resources 

and their interrelations, the quantities available from 

the several sources, and a determination of the 

present disposition of those resources. Geologic and 

hydrologic phases of the study included determinations of: The location, extent, and hydraulic 

characteristics of aquifers; the sources, rates, and 

areas of recharge; the rates and areas of discharge; 

the relation of ground-water to surface-water 

supplies; and the magnitude and direction of 

ground-water movement within the principal groundwater reservoirs.

Measures were taken to obtain a better definition of 

the distribution and use of surface water, principally 

by improving stream-measuring facilities, but also by 

the addition or relocation of gaging stations on 

streams, canals, and drains. Water use by several 

species of vegetation for which few or no data were 

available from previous studies was determined 

experimentally by measuring rates of use by these 

species when grown in tanks whose tops were set 

flush with the land surface in a natural environment.

The rate of evaporation from free water surfaces, 

notably from the Salton Sea, the regimen of the Salton 

Sea, and the effects of future water use in the Salton 

Sea basin were studied.

Chemical quality studies included ground-water and 

surface-water supplies, and a regional appraisal of the 

character of the total water resources. Salt-balance 

determinations' being made by irrigation districts 

when the investigation began, were supplemented, 

and some were made for other areas where needed.

PROJECT HISTORY

The lower Colorado River project was started July 

1,1960, with its headquarters in Yuma, Ariz. During 

the first year ground-water studies in the Yuma, 

Imperial and Coachella Valleys, and Parker-BlytheCibola areas were begun. Also begun were the studies 

pertaining to the surface-water supply of the project 

area and the studies for determining evaporation from 

the Salton Sea, consumptive use rates by 

phreatophytes, and chemical quality of both surfaceand ground-water supplies.

Progress reports on these studies were presented at 

public meetings held in December 1961, March 1963, 

and May 1964 at Yuma, Ariz.

In 1962 fieldwork pertaining to the study of 

evaporation from the Salton Sea was completed, and 

ground-water studies in the Coachella Valley were 

suspended pending the completion of a report on the 

water supply of that area by the California 

Department of Water Resources.

By mid-1964 the first of two electric analog models 

of the Yuma area was being built in the Phoenix 

hydrologic laboratory of the U.S. Geological Survey. 

Also, gravity, aerial magnetometer, Earth resistivity, 

and seismic surveys were being used to supplement 

the test drilling and other geologic investigations.

In 1966 because of newly acquired evidence 

regarding the hydrologic significance of the Algodones 

fault additional investigations in the Yuma area 

were undertaken. The additional studies, which lasted 

more than a year, were needed to determine the 

location and extent of the fault and its effect on the 

movement and chemical quality of the ground water. 

Geophysical exploration and test drilling, in 

cooperation with the U.S. Bureau of Reclamation, 

disclosed that this northwest-trending fault was a 

significant barrier to the movement of ground water. 

Incorporating the barrier effect of the fault into a 

second, more sophisticated electric analog model of 

the Yuma area made possible the satisfactory 

simulation of historical changes in water level in the 

Yuma area. The project studies in the Yuma area were 

supplemented by studies made at the request of and 

for the U.S. Section of the International Boundary and 

Water Commission. These later studies were 

concerned with determining rates and directions of
A8 WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

ground-water movement across segments of the 

international boundary under natural conditions and 

at various times during the development of 

ground-water and surface-water supplies both in 

Mexico and in the United States.

ACKNOWLEDGMENTS

Many agencies, groups, and individuals furnished 

records and cooperated with the U.S. Geological 

Survey during the project studies. Appropriate 

acknowledgment and appreciation of this help are 

given in each of the separate reports on the project. In 

this summary report, except for the few individual 

acknowledgments which follow, only a general 

acknowledgment is made.

The U.S. Bureau of Reclamation, Yuma project 

office, furnished information from its files, did some 

exploratory drilling, financed a reflection seismic 

survey, contributed financially toward the construction of an electric analog model of the Yuma area, and, 

in addition, maintained a close working relationship 

with the Survey throughout the investigation. Both 

the U.S. Section and the Mexican Section of the 

International Boundary and Water Commission 

provided valuable data from their files. The U.S. 

Section also provided financial assistance toward 

construction of the analog model.

The cooperation of the Colorado River Indian 

Agency, the Upper Colorado River Commission, 

several private consultants, and the various irrigation 

districts in making available needed data from their 

files is gratefully acknowledged. Appreciation is also 

extended to the many well drillers who had drilled, or 

were drilling, wells in the project area for making 

available their logs of wells and the results of wellcompletion tests. Acknowledgment and appreciation 

are given to the many farmers and other landowners 

for generously permitting access to their lands and 

wells, for furnishing data on their wells and farming 

practices, and for their cooperation in the scheduling 

of aquifer tests. Special credit and thanks are 

extended to Messrs. F. H. Olmsted and D. G. Metzger 

for providing much of the material presented in the 

section on geology and the related maps.

SUMMARY OF RESULTS

The following summary of the results of the project 

studies is based mainly on project reports, published 

as Professional Paper 486, chapters B-K, the titles of 

which are 

B. "Precipitation, Runoff, and Water Loss in the 

Lower Colorado River-Salton Sea Area"

C. "Hydrologic Regimen of Salton Sea, California" 

D. "Lower Colorado River Water Supply Its Magnitude and Distribution" 

E. "Salinity of Surface Water in the Lower Colorado

River-Salton Sea Area" 

F. "Consumptive Use of Water by Phreatophytes and

Hydrophytes near Yuma, Arizona" 

G. "Geohydrology of the Yuma Area, Arizona and

California" 

H. "Geohydrology of the Parker-Blythe-Cibola Area,

Arizona and California"

I. "Analog Simulation of the Yuma, Arizona, groundwater system" 

J. "Geohydrology of the Needles area, Arizona,

California, and Nevada" 

K. "Geohydrologic reconnaissance of the Imperial

Valley, California"

The chapters deal with separate subjects or areas in 

a comprehensive manner, and the reader is referred to 

them for more specific and detailed information. In a 

few instances, data used in this summary report postdate the periods covered by the project reports in 

order to make this summary more current.

MAGNITUDE AND DISTRIBUTION 

OF THE WATER SUPPLY

The water supply of the Colorado River system 

above compact point probably can be sustained at 13 

million acre-feet per year over long periods of time 

and at 14 million acre-feet per year for most years. 

This supply is available for depletions above compact 

point and for release to the lower basin States and 

Mexico. The division of this gross supply between the 

upper and lower service areas depends in part on the 

existence of facilities to enable use of the water in the 

upper service area and on provisions of the Colorado 

River Compact. The actual flow at compact point 

probably will exceed compact requirements most of 

the time until the upper service area's man-caused 

depletion of water supplies reaches 5 million acre-feet 

annually which is forecast for 1990 (U.S. Bureau of 

Reclamation, 1965). However, the supply is likely to 

be inadequate for meeting all the potential demands 

for water by the States before that date.

Distribution of Colorado River water below Davis 

Dam during 1961-63 is shown in figure 5 and is listed in 

table 1. Depletions of the river during the above 

period caused by use of water from the main stream in 

Arizona and California probably were comparable to 

depletions in 1960, which were about 1.1 million and 

4.9 million acre-feet, respectively. About 1.94 million 

acre-feet reached the international boundary.
SUMMARY REPORT AS OF 1971 A9

Oavis Dam

TO METROPOLITAN WATER DISTRICT 

OF SOUTHERN CALIFORNIA

25

FIGURE 5. Distribution of Colorado River water below Davis Dam, 1961-63. Widths of pattern indicate mean annual flows except those less than 100,000 acre-feet.

Numbers refer to items in table 1.
A10 WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

TABLE 1. Average annual flow in the lower Colorado River 

system, 1961-63

[Data are in acre-feet]

COLORADO RIVER BASIN

1. Colorado River below Davis Dam, Ariz.-Nev. _______..___ 8,438,000

2. Colorado River near Topock, Ariz.................................... 8,221,000

3. Bill Williams River near Alamo, Ariz............................. 19,860

4. Diversion to Metropolitan Water District of Southern California. 1,078,000

5. Colorado River below Parker Dam, Ariz.-Calif.l...................... 7,128,000

6. Diversion to Parker Valley, Ariz________________._ 463,300

7. Retnrn flow from Parker Valley, Ariz.2.-.-...................... 284,900

8. Diversion to Palo Verde Valley, Calif............................. 941,900

9. Colorado River below Palo Verde Dam, Ariz.-Calif._________ 5,871,000

10. Return flow from Palo Verde Valley, Calif.' .._-._-.._--.-_..__- 567,700

11. Colorado River below Cibola Valley, Ariz............................ 6,438,000

12. Colorado River above Imperial Dam, Ariz.-Calif _________. 6,424,000

13. Colorado River below Imperial Dam, Ariz.-Calif...................... 507,400

14. Return flow from North Gila Valley, Ariz.4--..................... 49,900

15. GilaRivernear Yuma, Ariz.« ._-._...._- ....................... 194,000

16. Return flow from South Gila Valley, Ariz.6 - - _.... ______... 39,520

17. Colorado River at Yuma, Ariz. ......-...-.-.......----..---...-... 822,600

18. Return flow through Yuma Main Canal wasteway, Calif.. ___ 220,800

19. Return flow from Reservation Division of Yuma project, Calif.'.. 51,500

20. Return flow through Pilot Knob powerplant and wasteway, Calif. 645,400

21. Colorado River at northerly international boundary.. _________ 1, 772,000

22. Diversion in Alamo Canal to Mexicali Valley, Baja Calif.......... 1,525,000

23. Return flow from Yuma Valley, ArizA........................... 172,200

24. Colorado River at southerly international boundary...... _. _. __ 223,400

25. Total flow to Mexico at southerly boundary .......................... 370,400

26. Total flow to Mexico ">.-............................. .............. 1,920,000

27. Gila Gravity Main Canal at Imperial Dam, Ariz.-Calif-.............. 871,600

28. Diversion to North Uila V&lley, Ariz............................. 87330

29. Diversion to Wellton-Mohawk area, Ariz. ______________ 414,600

30. Diversion to South Gila Valley, Ariz...............__......... 17,700

31. Diversion to Yuma Mesa, Ariz..........-.-.....---..-..-......... 310,600

32. All-American Canal near Imperial Dam, Ariz.-Calif.................. 5,048,000

33. Diversion to Reservation Division of Yuma project, Calif."-...,. 95,100

34. Yuma Main Canal at siphon-drop powerplant near Yuma, Ariz.. 573,700

35. Diversion to Yuma Valley, Ariz."................................ 350,000

36. All-American Canal above Pilot Knob wasteway, Calif............... 4,284,000

37. All-American Canal below Pilot Knob wasteway, Calif, (diversion to

Imperial and Coachella Valleys)--.................................. 3,603,000

_______________SALTON SEA BASIN, CALIF.___________________

38. Coachella Canal at head, near Greys Well-..-...-.......-.....-.-..... 529,300

39. Diversion from Coachella Canal to Imperial Valley- _______ 2,100

40. Coachella Canal below 6A check, near Niland.._....______ 380,500

41. Coachella Canal at milepost 87, near Mecca-____._______ 355,000

42. All-American Canal below Coachella Canal...._______.___ 2,966,000

43. All-American Canal above East Highline Canal "...__.______ 2,923,000

44. Total delivery to Imperial Valley (items 39 and 43)................... 2,925,000

_______________DRAINAGE TO SALTON SEA_____________

45. Drainage into Imperial Valley from Mexico..______________ 130,600

46. Inflow to Salton Sea from Imperial Valley "........................... 1,270,000

47. Inflow to Salton Sea from Coachella Valley .......................... 110,000

i A decrease of 15,100 acre-feet in the contents of Lake Havasu accounts for 5,000 

acre-feet of this total.

 Sum of flows in six channels, of which four enter the river above Palo Verde Dam 

and two enter below the dam but above the gaging station (item 9).

I Sum of flows in 12 channels partly estimated.

« Sum of flows in six channels three tributary to the Colorado River and three 

tributary to the Gila River.

 Sum of flows of the Gila River near Dome, Wellton-Mohawk Main Outlet drain, 

and minor flows in two wasteways in the Gila Gravity Main Canal. It includes return 

flow from the Wellton-Mohawk area and some runoff from local storms, but does not 

include return flows from North and South Gila valleys.

«Sum of flows in three channels 2 tributary to the Gila River and one tributary to 

the Colorado River.

i Sum of flows in two channels.

 Includes flows from three wasteways to the Colorado River (25,170 acre-ft) and 

water that flowed or was pumped across the international boundary to canals in 

Sonora, Mexico (147,000 acre-ft).

8 Sum of flows in the Colorado River and canals. (See footnote 8.) 

i° Flow reaching the international boundary (items 21 and 23) was 1.944,000 acre 

feet; flow leaving the boundary (items 22 and 25) was 1,895,000 acre-feet.

II Sum of flows in several small canals diverting from All-American and Yuma 

Main Canals. About 4,700 acre-feet of the total was diverted from Yuma Main Canal 

below siphon-drop powerplant and is included in item 34.

» Includes diversion for the'City of Yuma.

» Sum of flows below East Highline Canal and diversions above East Highline 

check.

14 Sum of flows in the Alamo and New Rivers and about 30 other channels.

w Sum of flows in the Whitewater River and 18 drains.

In more recent years, 1967-69, the average annual 

flow below Davis Dam has been very near 8 million 

acre-feet; depletions of the river caused by the use of 

main-stream water in Arizona and California have 

been comparable to the respective uses in 1961-63. 

Only slightly more than the 1.5 million acre-feet

guaranteed by the Mexican Water Treaty of 1944 has* 

been delivered at the international boundary. Thus, in 

recent years a flow of about 8 million acre-feet per 

year has been sufficient to meet current demands. 

However, future demands will be considerably larger, 

especially when the Central Arizona Project, under 

which an estimated 1.2 million acre-feet per year will 

be diverted from the river to central Arizona, becomes 

operative.

Considering probable upstream uses and assuming 

no supplemental supply from storage, the net supply 

of Colorado River water below Davis Dam for normal 

runoff conditions is estimated to be 10.2 million 

acre-feet for 1975 and 8.4 million acre-feet for the year 

2030. For dry conditions, the corresponding supplies 

are estimated to be 8.2 million and 6.4 million 

acre-feet. Thus, for periods of normal runoff, the 

supply appears to be adequate for meeting the 

demands of recent years in the lower basin plus the 

demands of the Central Arizona Project for a decade 

or two beyond 1975. However, for protracted dry 

periods, the supply will be inadequate after 

completion of the Central Arizona Project.

The amount of water required to satisfy basic 

allotments below Davis Dam (8.7 million acre-ft) and 

the losses associated with storage and conveyance of 

water below the dam (900,000 acre-ft) is 9.6 million 

acre-feet. Comparison of these figures of supply and 

basic allotments shows that the supply would be 

adequate during periods of near normal runoff until 

about 1980.

WATER LOSS

The beneficial use of water below compact point is 

accompanied by large losses, some of which are 

unavoidable. Evaporation from the river and from 

reservoirs consumes more than 1 million acre-feet per 

year, and riparian vegetation consumes more than 

500,000 acre-feet per year. Annual seepage from large 

canals between Imperial Dam and the areas to which 

the water is diverted amounts to 500,000 acre-feet. 

About 1.3 million acre-feet per year, most of which is 

return flow from irrigation in Imperial Valley, drains 

to the Salton Sea, where it evaporates. A large part, 

although not all, of this drainage is necessary to 

maintain the productivity of the irrigated land. 

However, all the inflow is needed to maintain the 

Salton Sea which provides substantial recreational 

opportunities at its present stage.

The disposal of water that seeps from canals varies 

considerably. Some of the seepage from canals near 

the Colorado River contributes to return flow to the 

river and to that extent does not deplete the available
SUMMARY REPORT AS OF 1971 All

supply. However, much of the seepage from canals is 

used consumptively by vegetation having little or no 

direct economic value or it drains to areas where the 

water is no longer available for further beneficial 

consumptive use. The U.S. Bureau of Reclamation and 

the irrigation districts have continuing programs for 

determining where large-scale leakage is occurring 

and for reducing or eliminating such leakage.

CONSUMPTIVE-USE RATES

Evaporation rates from the Salton Sea during the 

years 1961-62 computed by water-budget and energybudget methods differed by less than 5 percent. Data 

obtained by these methods, together with data on 

windspeed and vapor-pressure differences between 

saturated air at the water surface and the air above 

the water surface, were used to establish the 

empirical coefficient in the simplified mass-transfer 

equation. The mass-transfer method was then used to 

determine relative rates of monthly evaporation.

Annual evaporation determined by the first two 

methods also was used to establish a coefficient (0.64) 

for comparison of average annual evaporation from 

three sunken pans at widely separated sites on the 

shores of the Salton Sea with evaporation from the 

sea. Use of the pans was concluded to be the most 

practical method for continuing the measurement of 

annual evaporation from the sea, even though the 

method is not suitable for accurate determination of 

monthly rates of evaporation. The computed 

evaporation for 1961-62 and the pan data for 1948-62 

indicate that normal annual evaporation from Salton 

Sea is 5.78 feet (69 in.). This rate is markedly lower 

than that for Lake Mead, which is the nearest large 

body of water in a desert environment. The average 

annual evaporation from Lake Mead from 1948-62 was 

about 86 inches, or 17 inches more than the 

evaporation from the Salton Sea during the same 

period. Although some of the difference probably is 

due to small errors in the data used for computing the 

rates, most of the difference probably results from 

differences in salinity, in the volumes and 

temperatures of inflow and outflow, and in the mean 

distance the wind travels across the water.

Consumptive-use rates for five species of vegetation 

and rates of evaporation from bare soil and from free 

water surfaces were determined during a 6-year 

period, 1961-66, at two sites on the flood plain of the 

river between Yuma and Imperial Dam. Arrowweed, 

four wing saltbush, quailbrush, and bermuda grass 

were grown in large tanks, each about 1,000 square 

feet in area, at Imperial campsite. Average yearly

water use for four species of vegetation was as 

follows:

Type of vegetation

Depth to

water table

in (ft)

Average

yearly

water use

(in.)

Arrowweed (Pluchea sericea) ............. 5.5 96

Quailbrush (Atriplex lentiformis) .......... 3.5-5.5 44

Fourwing saltbush (Atriplex canescens) .... 3.5-5.5 38

Bermuda (Cynodondactylon) ............. 3.5 73

Cattail was grown in tanks, 100 square feet in area, 

at Mittry Lake site. Water in the tanks was 

maintained 0.2-0.3 foot above the land surface. 

Average annual use of water, including precipitation, 

ranged from 100 to 114 inches for tanks in which the 

vegetation appeared to be similar to the cattail 

vegetation outside the tanks.

Evaporation from bare soil tanks at Imperial 

campsite was found to vary greatly with depth to 

water below land surface. For the sand-silt-clay 

mixture in the tanks, which was considered to be 

representative of much of the flood-plain soil, annual 

evaporation rates averaged 20.0 inches with the water 

level 2 feet below land surface, 6.6 inches with the 

water level 3 feet below land surface, and 3.2 inches 

with the water level 4 feet below land surface. The 

foregoing rates exclude precipitation, which was 

significant for only a few months. Rates of evaporation 

for the 4-foot depth to water were lower than rates for 

similar depths to water computed by others in 

previous studies. Much of the wide range in 

evaporation at comparable depths indicated by other 

studies probably is due to differences in the degree of 

compaction and types of soil used in the various 

experiments.

The great influence of environmental factors on 

evaporation rates from free water surfaces was 

demonstrated by the large differences in rates of 

evaporation noted at Imperial campsite, which is 

relatively open to wind movement and not adjacent to 

open water, and at Mittry Lake site, which is 

surrounded by cattails and is adjacent to the lake. In 

1964, the Class A pan at Imperial campsite showed a 

yearly rate of evaporation of 114.52 inches, whereas 

the same type pan at Mittry Lake site showed only 

91.06 inches. The 10- by 10- by 1-foot buried tank 

adjacent to the standard pan at Mittry Lake site 

showed a yearly rate of only 66.37 inches. Differences 

in wind movement and air temperatures at the sites 

probably accounted for most of the differences in 

measured evaporation.
A12 WATER RESOURCES OF LOWER COLORADO RIVER - SALTON SEA AREA

Consumptive-use rates for other species of natural 

vegetation and for crops were based on rates 

computed by Blaney and Harris (1952) but were 

increased somewhat for alfalfa and cotton because of 

higher rates indicated in studies made by Erie, 

French, and Harris (1965). Because of further 

uncertainties regarding the cropped acreages, the 

variations in farming practices, and the types of crops 

grown, a uniform rate of 3.6 acre-feet per irrigated 

acre per year was concluded to be a satisfactory 

average rate for computing consumptive use by crops 

in the flood plain. In intensively cultivated areas 

where natural vegetation occupied only a small 

percentage of the area, a consumptive-use rate of 2.5 

acre-feet per acre per year was used for noncropped 

areas on the flood plain. On the Yuma Mesa, where 

about 20,000 acres of citrus is irrigated, consumptive 

use was computed on the basis of rates of use by the 

principal kinds of citrus that were irrigated.

WATER BUDGETS

Consumptive-use quantities of water within 

selected areas were computed by both the 

inflow-outflow method and the area-rate method. In 

the inflow-outflow method, consumptive use was 

computed as the residual between inflow and outflow 

items of the water supply. Depletions indicated by 

streamflow records were adjusted for exports from 

the areas and for changes in surface-water storage. 

Changes in ground-water storage, except in the Yuma 

area, were small enough to be ignored. In the 

area-rate method, consumptive use was computed by 

summing quantities obtained by multiplying rates of 

use and areas to which the rates applied. 

Consumptive-use quantities between Davis Dam and 

Imperial Dam computed by each of the two methods 

and the average of these quantities are shown in table 

2.

Differences in consumptive use computed by the 

two methods range from virtually nothing for the area 

between Davis Dam and Parker Dam to 150,000 

acre-feet for each of the areas between Parker Dam 

and Imperial Dam, and Davis Dam and Imperial Dam. 

The differences between the two methods for 

computing consumptive use are not always in the 

same direction. In the areas Davis Dam to the gaging 

station near Topock and the gaging station near 

Topock to Parker Dam, the differences are wholly 

compensating.

Loeltz and McDonald (1969) in analyzing this 

problem considered the probability that the 15-year 

means of surface-water depletions might differ from 

long-term means. They found an even chance that the

15-year mean might differ from a long-term mean by 

20,000 acre-feet or more, and 1 chance in 20 that it 

might differ by 60,000 acre-feet or more. Other 

possible sources of error were small consistent errors 

in measurement of river discharge. A consistent error 

of 1 percent would cause an error in the range of 

80,000 to 95,000 acre-feet in the computed depletion 

for each of the adjacent reaches.

Depletions of streamflow between Davis Dam and 

Imperial Dam are shown in figure 6. Random errors of 

measurement are indicated by the year-to-year 

differences in depletion, especially when the depletion 

increases significantly in one reach of the river and at 

the same time decreases in an adjoining reach. The 

difference of almost 200,000 acre-feet between the 

average depletion for the entire reach between 

1953-57 and the average depletion for 1958-62 

probably results from a change or changes in 

measurement or computational procedure at one or 

more points of measurement.

Other recognized sources of error are the estimates 

of consumptive-use rates and acreages to which the 

rates apply, and the estimates of unmeasured inflow 

and outflow. The latter estimates are rather small, 

however, and are therefore not as likely to be the 

cause of the larger differences. Although adjustments 

could be made to bring about a closer agreement 

between the consumptive-use estimates for each of 

the reaches, in view of the uncertainties regarding the 

preciseness of most of the budget items, such 

adjustments were concluded to be unwarranted.

A water budget for the Yuma area, showing a 

comparison between the two methods for computing 

consumptive use for the 16-year period 1951-66, is 

given in table 3. The budget differs from the budgets 

for the areas upstream from Imperial Dam principally 

in that changes in ground-water storage are 

significant. The virtual agreement between values 

obtained by the two methods for the Yuma area is 

fortuitous because studies of variability of the yearly 

differences between measured inflow to and outflow 

from the area showed that at the 95-percent 

confidence level the 16-year mean might differ as 

much as 37,000 acre-feet from the long-term mean.

A detailed water budget for Imperial Valley, Calif. 

was not made because of the reconnaissance nature of 

the investigation of that area. An approximation of the 

magnitude of the budget items is shown as follows:

[Items refer to table 1]

Measured inflow (items 44 and 45) 

Measured outflow (item 45)......

Residual ......................

Thousands of 

acre-feet

3,056

1,270

1,786
SUMMARY REPORT AS OF 1971 A13

TABLE 2. Consumptive use of water between Davis Dam and Imperial Dam

Colorado River valley between:

Budget items

Davis Dam Gaging station Davis Dam Parker Dam Palo Verde Parker Dam Davis Dam

and gaging nearTopock and and Palo Dam and and and

station near and Parker Dam gaging station Imperial Dam, Imperial Dam, Imperial Dam

Topock, Parker Dam, 1950-66 1957-66 below Cibola 1950-66 1950-66

1950-66 1950-66 Valley, Ariz.,

^^^ 1957-66 _______

	Inflow-outflow method

Measured inflow minus 

measured outflow (average annual streamflow depletion, 

adjusted ............

Unmeasured inflow 

minus unmeasured 

outflow: 

Surface water ......

Ground water ......

Consumptive use .

Natural vegetation .....

Irrigated crops .........

Evaporation ...........

181,000

15,000

15,000

211,000

188,000

12,000

41,000

151,000

19,000

5,000

175,000

8,000

(1)

140,000

332,000

34,000

20,000

386,000

Area-rate method

109 nnn

12,000

181,000

9ac nnn

6,000

-1,000

300,000

167,000

118,000

99 nnn

361,000

27,000

3,000

391,000

iqc nnn

qoi nnn

20000

686,000

44,000

-8,000

722,000

OCQ nnn

43Q 000

81 nnn

1,018,000

78,000

12,000

1,108,000

545 000

451 000 9R9 nnn

Consumptive use. 241,000 144,000 385,000 307,000 477,000 873,000

Consumptive use 

(average of 

both methods) . 226,000 160,000 386,000 304,000 434,000 798,000

1,258,000

1,183,000

 ^Negligible.

TABLE 3. Consumptive use of water in Yuma area, 1951-66

[Mean annual quantities, in thousands of acre-feet]

Inflow-outflow method

Inflow

Measured:

Surface ......

Unmeasured:

Surface water 

Ground water. 

Outflow

Measured:

Surface water 

Unmeasured:

Ground water . Change in storage 

Unmeasured:

Ground water

Consumptive use

+7,858

+2 

+11

-7,232

-70

-80 

489

Area-rate method

Natural vegetation and other noncropland 

Irrigated crops........................

Evaporation..........................

99

367

20

Consumptive use........................

Consumptive use (average of both methods)

486 

~488

The residual represents consumptive use on 432,000 

acres of cropland plus consumptive use in unplanted 

areas within the irrigated tracts. The rate of 4.1

acre-feet per acre, computed on the basis of cropland 

alone, is therefore somewhat higher than the 

consumptive-use rate for crops that would be obtained 

if the other acreages and rates of use within the 

irrigated tracts were included in the computations.

CHEMICAL QUALITY OF THE COLORADO RIVER

Under virgin conditions and prior to the closure of 

Hoover Dam, the chemical quality of the lower 

Colorado River varied substantially from season to 

season and year to year. Dissolved solids probably 

ranged from slightly less than 200 to more than 2,000 

mg/1 (milligrams per litre), and consisted mainly of 

calcium and bicarbonate at lower concentration levels 

and calcium, sodium sulfate, and chloride at higher 

concentration levels.

At Grand Canyon, where the chemical quality of the 

Colorado River is representative of the chemical 

quality of water that enters Lake Mead, the weighted 

average dissolved-solids concentration for the 40-year 

period 1926-65 was about 600 mg/1. The outflow from 

Lake Mead is more highly mineralized than is the 

inflow, and the dissolved-solids concentration 

increases downstream. Between Hoover and Imperial
A14

2 -

I I I I

WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA 

5 I I I

Parker Dam to 

Palo Verde Dam

Palo Verde Dam 

to Cibola

Cibola to 

Imperial Dam

4

-1

-1

1 I I I I

I I I

13

12

11

10

o> o n; m co $9 co CD CD CD I 1

FIGURE 6. Depletions of streamflow between Davis Dam and Imperial Dam

Dams, the dissolved-solids concentration generally 

has ranged between 600 and 900 mg/1 (tables 4, 5). 

The higher dissolved-solids concentrations immediately below Hoover Dam result mainly from evaporation 

from the surface of Lake Mead and solution of salts 

from its bed. These adverse effects are offset in part 

by precipitation of calcium carbonate in the lake; also, 

the solution of salts from the bed of the lake appears to 

be substantially less in recent years than during the 

first few years after the lake was formed.

A marked increase in the annual diversion of the 

Colorado River aqueduct during 1961-65 further 

lessened the quantity of water available in the main 

stream for dilution of somewhat saline return flows 

from irrigated areas downstream from Parker Dam. 

Development of new lands for irrigation, especially in 

Parker Valley, increased the quantity of dissolved 

salts in return flow to the river, thereby also 

contributing to the increasing salinity of the river

below Parker Valley. An indication of the increasing 

salinity of the river water between Hoover and 

Imperial Dams is shown by the increase in the 

difference between the dissolved-solids concentration 

below Hoover Dam and at Imperial Dam for the three 

5-year periods listed in the following table. Further 

increases in the differences between the sums of 

dissolved solids at the two sampling sites can be 

expected as the annual depletion of the river

Sampling 

site

Colorado River

below Hoover Dam 

Colorado River

at Imperial Dam

Difference.

Sum of dissolved solids (mg/1), 

by water years

1941-45 1951 -55 1961-55

im ...... 703

......... 726

658

706

714

824

23 48 110
SUMMARY REPORT AS OF 1971 A15

TABLE 4. Annual weighted-average chemical analyses for Colorado River below Hoover Dam, Ariz.-Nev.

[Results in milligrams per litre unless otherwise indicated. (estimated) signifies concentrations determined indirectly instead of by weighting individual

analyses]

Dissolved solids

Water 

year

1935 ...

1936 ...

1937 ...

1938 ...

1939 ...

1940 ...

1941 ...

1942...

1943...

1944...

1945...

1946 ...

1947. ..

1948...

1949...

1950...

1951...

1952...

1953...

1954...

1955 _ ,

1956 ...

1957...

1958...

1959...

1960 ...

1961...

1962...

1963...

1964 ...

1965. ..

Total flow 

(acre-ft)

 5,556,000

_ 6.282,000

... 5,826,000

_ 6,168,000

_ 8.473,000

... 7,694,000

...11.730,000

...17,880,000

_ 12,500,000

...14,450,000

...12,940,000

...11,290.000

...10,660,000

...12,750,000

_ 13,200,000

.. .12, 940, 000

_ 9,981,000

--14,370,000

_ 12,780,000

...10,690,000

... 9,276,000

... 7,818,000

_ 8,088,000

...12,270,000

... 9,757,000

... 9,251,000

_ 8,661,000

... 8,304,000

... 8,810.000

_ 8,234,000

... 7,917,000

s

1

i

7,674

8,653 

8,048 

8,519 

11,700 

10,600

16,200 

24,690 

17,260 

19,910 

17,870

15,600 

14,730 

17,570 

18,230 

17,870

13,790 

19,800 

17,650 

14,760 

12,810

10,770 

11,170 

16,940 

13,480 

12,740

11,960 

11,470 

12,170 

11,340 

10,940

§CO, 

_ej

1

13

13 

10 

11 

13 

13

11 

12 

13 

12 12

 10 

 12 

 11 

 11 

 11

13 13 

 13 

 13 

 13

 13 

 12 

11 

11 

11

10 

12 

10 

10 

10

g

e

_s

82

78 

102 

103 

102 

110

110 

103 

95 

92 93

 89 

 90 

 88 

 85 

 84

84 

83 

83 

88 

102

104 

96 

87 

84 

88

92 

101 

98 

93 

101

-3

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1

29

24 

25 

25 

26 

28

28 

27 

26 

28 30

 30 

 29 

 27 

 25 

 26

28 

27 

23 

25

27

" 32 

31 

24 

24 

25

27

26 

24 

27 

29

* §

S s 

a = 13 ' % * 

o o to &H

108 5.8

85 5.7 

93 5.4 

90 5.7 

93 6.1 

98 5.2

98 6.4 

98 

89 

90 5.9 

95

90 

96 

89 

84 

81

90 

 90 «4.5 

82 «4.2 

90 «5.0 

106 «5.0

117 «5.3 

110 «5.3 

86 4.2 

81 4.0 

87 3.9

92 4.6 

98 4.3 

96 4.3 

97 4.3 

115 5.4

8

S

1

§

J2 

«

169

152 

157 

153 

158 

159

153 

156 

158 

159 166

 162 

 161 

 157 

 156 158

167 

 160 

 162 

 164 167

170 

171 

158 

158 

158

160 

162 

160 

154 

156

Hardness 

as CaCOs

Sum

I 

1a

03

268

242 

314 

314 

321 

348

355 

329 

303 

299 

 302

 288 

 294 

 281 

 263 257

267 

 273 

 253 

 274 

 320

 350 

 320 

269 

261 270

288 

 311 

290 

292 

335

g 

1_o

Q

101 .

72 

74 

69 . 72 

77

79 

72 

64 

70 

 77 ,

 75 .

 78 . 

 71 . 

 67 . 

 66 .

72 .

 72 . 

 62 . 

 73 . 

 94 .

 103 . 

 98 . 

71 

67 

 72 .

 82 

 87 

86 

90 . 

108

g

V

so

a

fe

0.3 

.3

.3 

.3

.3

.4 

.3 

.4

.3 

.3

.4 

.3 

.3

.4

0

5,

V

1

g

3.3 

2.7

3 f

2.8 

3.2 

3.0

3.0 

2.6 

3.2 

3.4 3.0

 2.5 

 1.8 

 1.8 

 1.8 1.9

2.0 

 2.1 

 2.0 

 2.1 2.2

 3.7 

 2.2 

2.9 

3.2 2.5

3.5 

3.5 

2.7 

1.2 

1.6

P 

Jg

£ <3

693

596 

703 

696 

712 

761

766 

719 

673 

679 696

 664 

 688 

 649 

 615 606

663 

652 

632 

677 

778

837 

791 

661 

622 

656

694 

725 

700 

703 

814

M8SMM i&

s

694

599 

704 

696 

716 

762

767 

722 

673 

677 695

 662 

 680 

 646 

 615 606

639 

 645 

 604 

 652 753

 813 

 760 

634 

614 639

680 

727 

691 

691 

782

*«43

&A

1"

0.94

.81 

.96 

.95 

.97 

1.03

1.04 

.98 

.92 

.92 

.95

.90 

.92 

.88 

.84 

.82

.90 

.89 

.86 

.92 

1.06

1.14 

1.08 

.90 

.85 

.89

.94 

.99 

.95 

.96 

1.11

aa

.rl

|SI s

324

293 

358 

360 

362 

390

390 

367 

344 

344 356

 346 

 344 

 330 

 315 316

324 

318 

302 

322 

366

391 

367 

316 

308 

322

340 

359 

343 

328 

371

1

a o 

*

185

168 

229 

234 

232 

259

264 

239 

214 

214 

 220

 212 

 212 

 202 

 187 

 187

188 

187 

168 

188 

228

252 

227 

186 

178 

193

210 

226 

212 

202 

243

0

ll8 IP

«8.§8 '!--

O>

 1,070

 907 

 1,060 

 1,040 

 1,070 

1,140

1,140 

1,080 

1,010 

1,030 

 1,060

 1.030 

 1,040 

 985 

 939 927

977 

974 

938 

1,010 

1,150

1,230 

1,170 

985 

944 

983

1,040 

1,090 

1,050 

1,030 

1,210

increases. The concentration of dissolved-solids in the 

Colorado River at the northerly international 

boundary is substantially greater than it is at Imperial 

Dam mainly because moderate saline return flows 

from irrigation and ground water pumped by drainage 

wells are discharged into the river, the flow of which is 

greatly reduced by diversion to the All-American 

Canal and Gila Gravity Main Canal at Imperial Dam.

GEOLOGY 

LANDFORMS

The lower Colorado River-Salton Sea area is 

characterized by barren, rugged mountains a few 

hundred to several thousand feet high separated by 

broad desert basins in which lie the present flood 

plains of the Colorado River and its principal southern 

tributary, the Gila River. The types of landforms in 

the project area are shown in figures 7-10. In the 

Needles and Parker-Blythe-Cibola areas, the 

landforms are grouped as (1) mountains and hills, (2)

piedmont slopes and dissected uplands, (3) river flood 

plain, and (4) nand dunes (figs. 7, 8). In the Yuma area 

the landform types are similar, except that the second 

type is described as mesas and piedmont slopes (fig. 

9). In Imperial Valley the types are (1) mountains and 

hills, (2) low hills and dissected uplands, (3) mesas and 

piedmont slopes, (4) young lakebed (most of central 

Imperial Valley), and (5) sand dunes (fig. 10).

The mountains and hills are chiefly rugged 

exposures of hard igneous (plutonic and volcanic) 

rocks and metamorphic rocks but, in .the Yuma area, 

include less rugged exposures of semiconsolidated 

nonmarine sedimentary rocks.

In the Imperial Valley area the low hills and 

dissected uplands consist of exposures of slightly to 

strong deformed semiconsolidated marine and 

nonmarine sedimentary rocks. Within the area shown 

in figure 10 these rocks are generally finer grained 

than the semiconsolidated nonmarine sedimentary 

rocks of the Yuma area and, in places, form colorful 

badlands.
A16 WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA 

TABLE 5. Annual weighted average chemical analyses for Colorado River at Imperial Dam, Ariz.-CaUf.

[Results in milligrams per litre unless otherwise indicated. « (estimated) signifies concentrations determined indirectly instead of by weighting individual

analyses]

Dissolved solids

Water 

year

Total flow 

(acre-ft)

"3

discharge n 

a

OJ

o

85, 

a

o

"of

o

e

is

"3

;nesium (M

CiJ

"of

eP 3

o

M

g P

'o

O 

O

rbonate (H

OJ 

O

Hardness 

as CaCOa

Sum

6

C£ 

OJ

3?

3

g

0)

3

g

io

J3

6

1 2

 § 11 o"* .3^

 «« 3S,

ai

M g

g«

ium, 

agnesium

"03 °

carbonate

§

0>

o

o

 § 0

es-a

8 IP 

s-§8

8 £.'§

1941.

1942.

1943.

1944 .

1945.

1*946..

1947.

1948.

1949..

1950..

1951..

1952.

1953.

1954..

1956..

1957..

1958..

1900..

1901..

1902..

1903..

1904..

1965..

.. __ 11,060,000

..---16,980,000

..--.10,820,000

....13,240,000

.. _ 11,800,000

..-.10,160,000

__ 9',714,000

.-.--11,730,000

__ 12,270,000

-.-.11,500,000

.... 7,766,000

....13,040,000

....11,970,000

.... 8,950,000

.... 8,398,000

.-.. 6,323,000

.... 0,279,000

....10,707,000

.--. 8,240,000

.... 7,338,000

.... 0,527,000

.... 0,220,000

. r _. 0,012,000

.... 0,070,000

.... 5,700,000

15,270

23 , 460

14,950

18,230

16,300

14,040

13,420

10,100

10,940

15,890

10,730

17,970

10,540

12,300

11,600

8,710

8,673

14,790

11,390

10,110

9,010

8,591

9,133

8,370

7,964

 12

 12

14

11

11

13

12

13

13

13

14

14

14

10

10

15

13

20

 18

 16

16

15

10

16

 110

 103

90

92

91

87

92

89

88

84

86

85

83

86

95

100

110

93

91

93

98

99

100

95

104

 28

 27

20

28

29

30

31

28

28

27

28

29

29

28

33

34

34

27

25

20

27

29

27

28

31

 107

98

99

98

104

100

89

88

101

100

95

105

121

137

130

117

107

112

120

133

129

131

150

 5.5

 105

97

4.1

5.3

5.9

4.1

3.3

6.4

2.9

5.2

4.4

4.2

4.5

5.2

5.6

5.4

4.9

 4.5

 4.7

 4.9

 5.5

 5.2

 5.1

 5.7

 153

 156

158

105

163

160

165

165

165

163

172

169

170

171

170

173

175

171

104

103

167

104

107

105

168

 363

 336

312

306

300

295

310

292

281

265

281

283

273

287

333

375

364

304

 288

 299

 323

328

320

324

364

 87

 79

72

76

82

83

89

82

74

75

87

84

79

87

106

126

126

97 90

 104

120

118

122

142

 0.3

.3

.3

.3

.2

.2

.2

.3

.3

.3

.3

.4

.3

.3

.4

.6

.4

.4

.4

.6

.0

.5

.4

 2.5

 1.9

1.8

2.5

1.5

1.0

1.3

1.5

1.8

1.4

1.1

1.4

1.4

1.3

1.5

1.7

1.1

1.9

 1.7

 1.6

 2.0

1.8

1.2

1.4

1.1

788

743

696

699

699

692

726

690

663

637

706

700

680

720

818

917

884

763

746

764

821

814

799

835

912

791

742

698

700

701

692

725

690

663

637

688

684

063

699

795

886

870

750

710

739

797

820

804

806

894

1.08

1.01

.95

.95

.95

.94

.99

.94

.90

.87

.94

.93

.90

.95

1.08

1,20

1.18

1.02

.97

1.01

1.08

1.12

1,09

1.10

1.22

 390

 368

346

344

346

340

357

337

334

320

330

331

32C

330

372

404

414

343

330

339

356

366

360

352

387

 264

 240

217

210

212

210

222

202

200

187

188

192

186

190

233

262

270

203

196

205

218

232

224

216

249

 i , 200

 1,120

1,050

1,070

1,070

1,050

1,100

1,060

1,010

985

1,050

1,050

1,020

1,070

1,200

1,340

1,340

1,140

1,080

1,130

1,220

1,260

1,240

1,240

1,380

The mountains and hills of the lower Colorado 

River-Salton Sea area are flanked by broad piedmont 

slopes having gradients ranging from 200 feet per 

mile to less than 10 feet per mile. At many places near 

the flood plains the piedmont slopes merge with, or 

are more sharply bounded by, river terraces and other 

slopes of low gradient, which locally are termed 

"mesas." Yuma Mesa in the Yuma area and East Mesa 

and West Mesa in the Imperial Valley area are the 

most extensive of these gently sloping surfaces; 

narrower terraces extend along the margins of the 

Colorado River flood plain north of the Yuma area. 

Also grouped with the piedmont slopes in the Needles 

and Parker-Blythe-Cibola areas are dissected uplands 

underlain by nonmarine and marine sedimentary 

rocks. In the Yuma area exposures of similar rocks are 

more rugged and hilly than in the Needles and ParkerBlythe-Cibola areas and are grouped instead with 

mountains and hills (fig. 9).

Upstream from Yuma the Colorado River flood plain 

ranges in width from less than 1 mile, where it is 

flanked by mountains and hills, to about 9 miles; 

downstream from Yuma the flood plain widens to 

merge with the broad fan-shaped subaerial delta of the

Colorado River, which separates the Gulf of California 

from Imperial Valley. The flood plain ranges in 

altitude from about 90 feet above mean sea level at the 

southerly international boundary to jnore than 500 

feet in the northern part of the Needles area. 

Generally, the flood plain is 50 to 80 feet below the 

adjacent river terraces, such as Yuma Mesa.

Central Imperial Valley is the bed of prehistoric 

Lake Cahuilla, whose shorelines are 42 to 50 feet 

above mean sea level. At some places, particularly 

along the southwest margin of the Salton Sea, the old 

lakebed has been modified slightly by alluvial 

processes; the resulting surfaces are shown in figure 

10 as mesas and piedmont slopes. The lakebed slopes 

north-northwestward from the international boundary 

to the Salton Sea at an average gradient of 1.7 feet per 

mile and is dissected by the Alamo and New Rivers, 

which have cut trenches as much as 40 feet deep into 

the soft silty lacustrine deposits.

In the lower Colorado River-Salton Sea area, as in 

most desert areas, wind is an important agent of 

erosion and deposition, especially where sandy alluvial 

or shoreline materials are exposed. The thicker 

accumulations of windblown sand are shown in figures
SUMMARY REPORT AS OF 1971 A17

R. 65 E. R. 66 E. R. 21W.11430 R. 20 W.

EXPLANATION

35 00 

|||| T. dissected uplands

Base from U.S. 

Geological Survey

T. 

13 

N.

R. 19 W. 

Geomorphology 

by D. G. Metzger

FIGURE 7. Landforms in the Needles area.
A18 WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

114°30' 114°15'

114 45

45

Mountains and hills 

5 10 MILES 

I _____| 

I I 

0 5 10 KILOMETRES

Geomorphology by D. G. Metzger 

FIGURE 8. Landforms in the Parker-Blythe-Cibola area.
SUMMARY REPORT AS OF 1971

30'

A19

EXPLANATION

Geomorphology by F. H. Olmsted

Thick accumulations of windblown sand.

Thin sheets and small dunes not shown

River flood plains

Exposures of younger deposits of the 

Colorado and Gila Rivers

Mesas and piedmont slopes

Undissected to strongly dissected alluvial surfaces and river 

terraces. Includes exposures of older deposits of the Colorado and Gila Rivers and local ephemeral streams and also 

thin sheets of windblown sand and small dunes

Mountains and hills

Rugged exposures of pre-Tertiary crystalline rocks and Tertiary volcanic rocks; less rugged exposures of Tertiary sedimentary rocks

FIGURE 9. Landforms in the Yuma area.
WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

15' RIVERSIDE CO 115°00' 

IMPERIAL CO

114 45

UNITED STATES 

 "MEXICO Geomorphology by J. H. Robison

and F. H. Olmsted 15 MILES

5 10 15 KILOMETRES 

EXPLANATION

Thick accumulations of windblown sand. Thin

sheets and small dunes not shown

Bed of prehistoric Lake Cahuilla where essentially unmodified

by alluvial processes

Low hills and dissected uplands

Exposures of slightly to strongly deformed sedimentary rocks

of the late Tertiary and Quaternary age, in places forming

colorful badlands

Mountains and hills

Rugged exposures of dense pre-Tertiary crystalline rocks and 

Tertiary volcanic rocks. Includes domes of obsidian at 

south end ofSalton Sea

Mesas and piedmont slopes

Undissected to slightly dissected alluvial surfaces and terraces. 

Includes thin sheets of windblown sand, small dunes, and 

young lakebed where modified by alluvial processes

FIGURE 10. Landforms in the Imperial Valley area.

7-10 as sand dunes; thinner sheets, generally less than 

10 feet thick, are not differentiated from the surfaces

on which they lie. The largest and most extensive 

dunes are the Sand Hills of the southeastern Imperial
SUMMARY REPORT AS OF 1971 A21

Valley area, which form a belt more than 40 miles long 

and generally about 5-6 miles wide. Some of the dunes 

are 300 feet thick.

ROCK UNITS AND OCCURRE NCE OF GROUND WATER

The earth materials of the lower Colorado 

River- Salton Sea area comprise a basement complex 

of pre-Tertiary crystalline rocks, an overlying 

sequence of slightly to moderately deformed 

sedimentary and volcanic rocks of Tertiary age, and 

virtually undeformed alluvial and windblown deposits 

of late Tertiary and Quaternary age, which were 

deposited after the Colorado River entered the area. 

The crystalline rocks include a wide variety of 

metamorphic, plutonic, and dike rocks. All are dense 

and contain only small amounts of water in fractures 

and weathered zones. The sedimentary and volcanic 

rocks of Tertiary age vary lithologically from slightly 

consolidated nonmarine and marine beds and 

volcanic-ash beds to dense lava flows and beds of 

welded tuff; they are similarly variable in 

water-bearing characteristics. Some of the coarsegrained nonmarine beds are capable of yielding 

moderate amounts of fresh ground water. Other, 

indurated beds, such as the lava flows and welded tuff, 

are as poorly watered bearing as the pre-Tertiary 

crystalline rocks and, like the crystalline rocks, may 

form the floor and walls of the ground-water 

reservoir. The virtually undeformed alluvial deposits 

(including some lake deposits in Imperial Valley) 

constitute the upper, principal part of the 

ground-water reservoir in the area. The beds of coarse 

sand and gravel, deposited chiefly by the Colorado 

River, are highly permeable and yield copious 

quantities of water to irrigation wells and other large 

wells.

NEEDLES AND PARKER-BLYTHE-CIBOLA AREAS

In the Needles and Parker-Blythe-Cibola areas, the 

bedrock that forms the boundaries of the 

ground-water reservoir is made up of igneous and 

metamorphic rocks, including metamorphosed Paleozoic and Mesozoic rocks, and it also includes deformed 

indurated sedimentary and volcanic rocks of Tertiary 

age. Where exposed, these rocks form the mountains 

and hills shown in figures 7 and 8.

The rock units exposed as piedmont slopes and 

dissected uplands (figs. 7, 8) include Miocene(?) 

fanglomerate, Bouse Formation, and older alluviums 

of the Colorado River and its tributaries. Locally, 

these units are overlain by eolian sand and sand 

dunes. Younger alluvium of the Colorado River 

underlies the river flood plain (figs. 7, 8).

The Miocene(?) fanglomerate consists mainly of a 

cemented, poorly sorted gravel composed of angular 

to subrounded pebbles and some fine-grained 

material. The fanglomerate is believed to have come 

from a nearby source, and it antedates the Colorado 

river. Locally, the fanglomerate is a good aquifer. For 

example, wells near Parker, Ariz., that tapped this 

acquifer yielded 15 (gal/min)/ft of drawdown.

The Bouse Formation of Pliocene age was deposited 

in an embayment of the Gulf of California, and it 

extends not only upstream along the present Colorado 

River north of the Needles area, but also into adjacent 

desert basins. The Bouse comprises a basal limestone 

overlain by interbedded clay, silt, and sand and a 

distinctive tufa. The maximum known thickness is 

more than 760 feet beneath the central part of Parker 

Valley. The lower part of the formation is generally 

poorly permeable, but the upper part is fairly 

permeable where sand is more abundant, A sandy 

zone in the Bouse in Parker Valley yielded water at 

the rate of 13 (gal/min)/ft of drawdown.

As the water in the Bouse Formation embayment 

began to recede, the Colorado River entered the 

project area. Eventually, the river eroded much of the 

Bouse Formation, and, although the mountains rose 

relative to the basins, the rate of rise was so slow that 

the river was able to maintain its course by cutting 

downward into the dense rocks of the mountains, 

thereby carving the present intervalley canyons.

The deposits of the Colorado River and its 

tributaries are divided into older and younger 

alluviums, which represent several long periods of 

degradation and aggradation by the Colorado River. 

Because of the several periods of degradation, much of 

the original thickness of the alluvial deposits has been 

eroded from the area. Although the alluviums 

represent distinctive geologic units, they are 

sufficiently permeable to constitute a common aquifer. 

The greatest saturated thickness of the alluviums is 

about 600 feet, near Blythe, Calif.; elsewhere, the 

thickness is much less.

The most abundant material in the alluviums is 

sand, and properly constructed wells that tap 

sufficient thickness of clean medium to coarse sand 

yield water at a rate of a few tens of gallons per 

minute per foot of drawdown. Where saturated, 

coarse gravel of the alluviums is the most productive 

water-yielding material in the area. Yields of more 

than 100 (gal/min)/ft of drawdown have been obtained 

from wells tapping coarse-gravel aquifers.

YUMAAREA

The crystalline rocks of pre-Tertiary age form the 

boundaries of the ground-water reservoir in the Yuma
A22 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

area. The ground-water reservoir consists of two 

major subdivisions the poorly water-bearing rocks of 

Tertiary age and the water-bearing deposits of 

Pliocene to Holocene age.

The first subdivision the lower part of the 

reservoir includes the sedimentary and minor 

volcanic rocks that were deposited before the 

Colorado River entered the area. In generally 

ascending order, the rock units are (1) nonmarine 

sedimentary rocks, (2) volcanic rocks, (3) older marine 

sedimentary rocks, (4) Bouse Formation (younger 

marine sedimentary rocks), (5) transition zone, and (6) 

conglomerate of Chocolate Mountains. At most places 

these units either contain highly mineralized water, 

are too poorly permeable, or lie at too great a depth to 

be significant potential sources of ground water. 

However, in the northern part of the area some of the 

coarse-grained nonmarine sedimentary rocks and a 

conglomerate in the basal part of the Bouse Formation 

are moderately permeable and contain fresh water 

(less than 1,800 mg/1 dissolved solids).

The second subdivision, or upper part of the 

ground-water reservoir, consists of (1) older alluvium, 

(2) younger alluvium, and (3) windblown sand. The 

older alluvium underlies most of the mesas and 

piedmont slopes and represents several depositional 

cycles, separated by periods and erosion. The younger 

alluvium represents the most recent depositional 

cycle. It underlies the flood plains of the Colorado and 

Gila Rivers, the ephemeral washes of the piedmont 

slopes, and the much more extensive alluvial fans 

adjacent to the western Cargo Muchacho Mountains 

and in southern Gila Mountains. The windblown sand 

forms dunes, the largest of which are the Sand Hills 

west of Yuma and an unnamed set of dunes just north 

of the southerly international boundary (fig. 9). 

Windblown sand also forms thin sheets on Yuma Mesa 

and Upper Mesa and forms small dunes in Yuma 

Valley and on the flood plain northeast of Yuma; these 

are not shown in figure 9.

Beneath the central part of the Yuma area, the 

upper part of the ground-water reservoir also is 

divided hydrologically into three zones, which are, in 

ascending order: The wedge zone, the coarse-gravel 

zone, and the upper, fine-grained zone. Outside the 

central area the coarse-gravel zone is absent in most 

places, and the upper part of the reservoir is not 

divided but is classified instead as older alluvium 

undivided.

The wedge zone is composed of older alluvium and 

extends to depths of about 2,500 feet south and 

southwest of Yuma. The lower part of the zone 

contains more silt and clay than the upper part, but in

general the fine-grained strata are not sufficiently 

extensive or thick to cause significant hydraulic 

separation. The upper part of the zone locally contains 

coarse-gravel strata similar to those in the overlying 

coarse-gravel zone.

The coarse-gravel zone, which is the principal 

aquifer beneath the river flood plains and Yuma Mesa, 

is a complex of gravel bodies of different ages, 

deposited by the Colorado and Gila Rivers. Beneath 

Yuma Mesa the coarse-gravel zone is within the upper 

part of the older alluvium, but beneath the flood plains 

the zone may include a basal gravel of the younger 

alluvium. The zone ranges in the thickness from 0 to 

possibly more than 150 feet; its top lies at an average 

depth of 100 feet beneath the flood plains and 170 to 

180 feet beneath Yuma Mesa.

The upper, fine-grained zone includes both the 

younger alluvium beneath the river flood plains and 

the uppermost part of the older alluvium beneath 

Yuma Mesa. The zone averages about 100 feet in 

thickness beneath the flood plains and 170 to 180 feet 

beneath Yuma Mesa. Sand and silt are the most 

abundant materials, although beds of silty and sandy 

clay and sandy gravel are extensive in parts of the 

area. Some clay beds in the zone underlie areas of 

several tens of square miles but do not appear to cause 

significant hydraulic separation, probably because 

they are fairly sandy in places.

IMPERIAL VALLEY AREA

The pre-Tertiary crystalline rocks of the Imperial 

Valley area are overlain by trough-filling deposits 

estimated, on the basis of geophysical evidence, to be 

more than 20,000 feet thick locally. These deposits are 

dominantly nonmarine and, beneath the central part 

of the valley, mostly Pliocene to Holocene in age. For 

hydrologic purposes, the deposits are grouped into 

three broad categories: (1) a lower sequence composed 

chiefly of nonmarine sedimentary rocks of early to 

middle Tertiary age but also including volcanic rocks 

and minor marine sedimentary rocks; (2) a middle 

marine unit, the Imperial Formation, of late Tertiary 

(Miocene or Pliocene) age; and (3) an upper sequence 

composed of predominantly nonmarine deposits of late 

Tertiary (Pliocene) and Quaternary age. The upper 

sequence constitutes the main part of the 

ground-water reservoir beneath Imperial Valley.

The lower sequence, exposed in the mountains and 

hills on the margins of the valley, is, if present, far too 

deep beneath the central part of the valley to be a 

possible source of ground water. Moreover, the rocks 

there would be expected to have extremely low 

permeability and to contain saline water.
SUMMARY REPORT AS OF 1971 A23

The marine Imperial Formation may be in part 

equivalent to the Bouse Formation of the Yuma, 

Parker-Blythe-Cibola, and Needles areas. Although 

the formation is exposed on the west side of Imperial 

Valley, the Imperial Formation has not been 

recognized in several oil test wells, as much as 13,443 

feet deep, in the central part of the valley. If present, 

the Imperial Formation would form an effective floor 

of the upper part of the ground-water reservoir, 

owing to its generally low permeability and probable 

content of saline water.

The upper sequence, which overlies the Imperial 

Formation, is predominantly nonmarine but includes 

some marine strata and evaporite beds representing, 

respectively, periodic incursions of the Gulf of 

California and intermittent lakes. In the marginal 

parts of the Imperial Valley area, the nonmarine 

deposits are of local derivation, but most of the 

deposits in the central part of the valley were brought 

in by the Colorado River. In general, the deposits of 

the Colorado River are finer grained and better sorted 

than the locally derived deposits.

CHEMICAL QUALITY OF GROUND WATER

Chemical analyses of samples of ground water 

obtained within short distances of one another in the 

project area often show a wide range in the 

percentage and concentration of the six ionic 

constituents that make up the bulk of the dissolved 

solids. Except for relatively small quantities of ground 

water that were derived locally, the water in the 

valleys upstream from the Yuma area is derived 

almost wholly from the Colorado River, whereas in the 

Yuma area the water is derived from both the 

Colorado and the Gila Rivers.

The observed wide range in chemical quality of 

ground water in areas where the source obviously was 

the Colorado River can be explained as the result of 

one or more of the following processes: (1) 

Concentration of dissolved solids by evapotranspiration, (2) softening, (3) carbonate precipitation, (4) 

sulfate reduction, (5) hardening, (6) re-solution of 

precipitated salts, (7) oxidation of dissolved organic 

substances, and (8) mixing of waters of different 

chemical composition.

By beginning with a weighted average chemical 

analysis of recent Colorado River water and by using 

several combinations of the first five processes carried 

out to various degrees, most types and dissolvedsolids concentrations of ground water derived from 

the Colorado River can be duplicated. Sulfate 

reduction appears to be a major process in the

chemical alteration of Colorado River water to a water 

containing fewer dissolved solids than the river.

Chemical analyses of water from wells in the 

Needles area suggest that the ground water there is 

generally of better quality than that in the 

downstream valleys. About half of the 95 

ground-water samples analyzed contained dissolved 

solids of less than 1,000 mg/1 and 6 had less than 500 

mg/1. On the other hand, 6 analyses showed 

dissolved-solids concentrations between 2,000 and 

3,290 mg/1.

Ground water acceptable for domestic use, public 

supply, or irrigation can be found at some depth in 

most parts of the Parker-Blythe-Cibola area. 

However, there are areas beneath which water of 

satisfactory quality is limited to thin strata or is not 

available. Much of the shallow ground water beneath 

the flood plain is relatively poor in quality except near 

the river or where it has been freshened as a result of 

irrigation. Shallow ground water in the nonirrigated 

southern part of Parker Valley commonly is several 

times more mineralized than river water. Shallow 

ground water of poor quality is also common beneath 

the nonirrigated land in Cibola Valley and in the 

southern part of the Palo Verde Valley.

In Parker Valley water from the principal gravel 

zone is generally similar to, but somewhat more 

mineralized than, present-day Colorado River water. 

However, near the eastern margin of Parker Valley 

south of Bouse Wash, in the southern part of Palo 

Verde Valley, and in Cibola Valley, the water in the 

principal gravel zone contains sufficient chloride to 

make it unfit for most domestic uses and is marginal to 

unsatisfactory for sustained irrigation. Near Blythe, 

Calif., water beneath the principal gravel zone 

contains considerably less sulfate and somewhat less 

dissolved solids than Colorado River water. Beneath 

the piedmont slopes, where local recharge moves 

toward the flood plain, the chemical quality of the 

ground water is commonly different from, and less 

concentrated than, Colorado River water.

Fluoride concentrations in excess of limits 

recommended by the U.S. Public Health Service 

(1962, p. 8) for drinking water on interstate carriers 

have been noted in many samples of water obtained 

from units older than the Colorado River deposits, 

such as the Bouse Formation and the Miocene(?) 

fanglomerate.

Fresh water (less than 1,800 mg/1 dissolved solids) 

extends to depths of more than 2,500 feet in the 

south-central and southwestern parts of the Yuma 

area. Most of this water is in the wedge zone, but the 

overlying, more permeable coarse-gravel zone yields
A24 WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

much more water to wells. In the northern part of the 

area the water in the wedge zone is substantially 

fresher than that in the coarse-gravel zone, but in the 

southern part the chemical quality of the water in the 

two zones is virtually identical.

Ground water in the coarse-gravel zone beneath 

South Gila Valley and beneath eastern North Gila 

Valley generally contains more than 1,800 mg/1 but 

less than 3,600 mg/1 of dissolved solids. Elsewhere in 

the northern part of the Yuma area, the water in the 

coarse-gravel zone contains less than 1,800 mg/1. 

Water in the overlying fine-grained zone locally is 

more highly mineralized than water in the 

coarse-gravel zone. Beneath Yuma Valley the 

chemical quality of water in the coarse-gravel zone 

and in the overlying fine-grained zone is not well 

known, but the freshest water (commonly containing 

less than 900 mg/1 of dissolved solids) occurs near the 

Colorado River.

Beneath the irrigated parts of Yuma Mesa, the 

ground water is similar to Colorado River water in 

which the dissolved solids have become concentrated 

by evapotranspiration. Outside the irrigated area and 

at depths beneath the irrigated area sufficiently deep 

that the native water has not been displaced by the 

infiltration of irrigation water, the concentration of 

dissolved-solids is less than 1,800 mg/1, and chloride, 

rather than sulfate, is the major anion.

Infiltration of local runoff has resulted in a few 

limited zones, such as the one beneath Fortuna Wash, 

12 miles east of Yuma, where a lens of water 

containing only a few hundred milligrams per litre of 

dissolved solids has displaced water containing a much 

higher concentration of dissolved solids.

Beneath most areas in central Imperial Valley, the 

ground water contains sufficient dissolved solids to 

make it unsatisfactory as either a domestic or an 

irrigation supply. Several test wells, drilled to depths 

of as much as 1,000 feet, in the southern and western 

parts of central Imperial Valley yielded water 

containing 5,000 mg/1 or more of dissolved solids.

The largest known body of fresh ground water in 

the Imperial Valley area is beneath the southeastern 

part of East Mesa. Fresh water extends from a few 

tens of feet below land surface to more than a 1,000 

feet below land surface near the head of the Coachella 

Canal. The other principal areas of fresh ground water 

are on the west side of the valley. They are in the 

Lower Borrego Valley, the San Felipe Creek area, and 

the Coyote Wells area. Ground water beneath the 

developed part of the Coyote Wells area generally 

contains less than 400 mg/1 of dissolved solids. Water 

from this area is hauled by tank truck to communities

as far away as Calexico, Calif., and Mexicali, Baja 

California, Mexico, for drinking water.

HYDRAULIC PROPERTIES OF ROCKS

Analyses of test-drilling data, pumping tests, and 

the specific capacities of existing wells indicate that 

some of the gravel deposits of both the Colorado and 

Gila Rivers, whether classified as younger or older 

alluviums, are highly transmissive. The more 

permeable deposits, commonly 10-70 feet thick, have 

hydraulic conductivities of about 10,000 (gal/d)/ft2 . 

Transmissivities of these deposits, computed from 

pumping tests of wells, ranged from about 100,000 or 

200,000 (gal/d)/ft to about 1 million (gal/d)/ft.

Hydraulic-conductivity values of sand strata range 

widely but generally are a few hundred gallons per 

day per square foot. However, some clean sands at 

moderate depths have conductivities of 1,000 

(gal/d)/ft2 or more.

Transmissivity values for the younger and older 

alluviums of the Colorado river and its tributaries in 

the Yuma area are shown in figure 11. The values are 

the sums of transmissivity values computed for the 

coarse-gravel zone and the wedge zone that were 

simulated in the electric analog model of the Yuma 

areas. Practically all ground-water movement in the 

Yuma area occurs in these zones.

Large-diameter wells that tap 10 feet or more of the 

highly permeable gravel can be expected to yield 30 or 

more (gal/min)/ft of drawdown. Specific capacities 

of several hundred gallons per minute per foot of 

drawdown are obtainable in some parts of all the 

major river valleys. A few of the more favorably 

located wells in the Yuma area have specific capacities 

of about 400 (gal/min)/ft of drawdown. Wells that tap 

100 feet or more of clean medium to coarse sand 

commonly have specific capacities of a few tens of 

gallons per minute per foot of drawdown. In the 

central part of Imperial Valley, where sand and silt 

constitute most of the water-bearing material, specific 

capacities range from a fraction of a gallon to several 

gallons per minute per foot of drawdown.

GROUND-WATER RESOURCES 

VIRGIN CONDITIONS

Under virgin (natural) conditions the principal 

source of ground water in the lower Colorado River 

basin was the Colorado River. Sources of recharge 

directly from precipitation, from the infiltration of 

tributary streams, and from underflow from tributary 

areas were only very minor. Recharge from the 

Colorado River occurred by direct infiltration and by
SUMMARY REPORT AS OF 1971 A25

114-45

32° 45

Line of equal transmissivity, in Alluvial escarpment 

thousands of gallons per day per foot

FIGURE 11. Transmissivity values for the younger and older alluviums in the Yuma area.

infiltration in flooded areas. The latter was a 

significant source of recharge in the lower lying parts 

of the flood plain because, prior to the construction of

upstream reservoirs, the river annually flooded 

substantial parts of the plain and filled abandoned 

channels.
A26 WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

The recharge both from direct infiltration of water 

from the river and from floodwater was consumptively 

used mainly by transpiration of natural vegetation 

or by evaporation from wet soil. Discharge by 

transpiration of natural vegetation in Yuma Valley 

is estimated to have been between 100,000 and 

150,000 acre-ft/yr. Half this discharge is estimated 

to have been supplied by direct infiltration from 

the river. Direct infiltration of river water which 

supplied evapotranspiration requirements of natural 

vegetation in Parker Valley was about 100,000 

acre-ft/yr. Similar conditions existed in the other 

major flood-plain valleys. Thus, under virgin 

conditions, the Colorado River was a losing stream 

throughout much of its course through the major river 

valleys.

CONDITIONS DURING DEVELOPMENT

The completion of Hoover Dam in 1935 provided a 

major control for river flows, thereby eliminating both 

the annual floods that formerly inundated the lower 

lying lands of the downstream valleys and the 

recharge from infiltration of floodwater.

Although irrigation by diverting river water to the 

various valleys had been practiced since before the 

turn of the century, the newly acquired ability to 

adequately control flows encouraged the rapid 

expansion of irrigation agriculture. By 1960 most of 

the flood-plain valleys in the Yuma area, the flood 

plain of Palo Verde Valley, and the central part of 

Imperial Valley were nearly fully developed, and 

almost 20,000 acres on the Yuma Mesa was being 

irrigated. Irrigation was being practiced on a limited 

scale in Mohave and Cibola Valleys and on a moderate 

scale in Parker Valley. Canals for conveying large 

quantities of river water to remote areas had been 

completed. As a result, the ground-water system, 

which, under virgin conditions, had been recharged 

from flooding, now was recharged from infiltration of 

water diverted from the river which was not used 

consumptively by crops. In Mohave and Cibola Valleys 

this recharge was negligible, but in Parker Valley it 

was about 200,000 acre-ft/yr. In Palo Verde Valley 

and in the flood-plain valleys of the Yuma area, the 

recharge ranged from 2 to 5 acre-feet per acre 

irrigated per year, or from about one hundred 

thousand to several hundred thousand acre-feet 

annually.

A notable example of the additional recharge to 

ground water that resulted from an expansion 

irrigated acreage is the increase in ground-water 

recharge beneath Yuma Mesa. From 1942, when only 

1,500 acres was irrigated, until 1954, when about 

17,000 acres was irrigated, the yearly recharge

increased from 8,000 to 177,000 acre-feet. For the 

5-year period beginning in 1960, the recharge 

averaged 226,000 acre-ft/yr but for the next several 

years declined to somewhat less than 200,000 

acre-ft/yr, mainly because of improved irrigation 

practices.

The initial effect of increased recharge from 

irrigation in all areas was a rise in ground-water 

levels. Eventually, water levels in parts of each area 

rose into the root zone sufficiently to impair crop 

growth. Drainage systems, some of which were 

extensive, were constructed to keep water levels at 

satisfactory depths. Thus, much of the increase in 

ground-water recharge from irrigation eventually was 

balanced by a similar increase in ground-water 

discharge to drains or to drainage wells.

Increases in ground-water storage that resulted 

from increased recharge were generally limited to the 

quantities of water contained in a 5 to-10-foot-thick 

volume of the flood-plain deposits, because rises in 

excess of the above range generally caused water 

levels to invade the root zone of crops, which then 

prompted remedial action for lowering water levels.

One area where the preceding generalization does 

not hold is Yuma Mesa, where, prior to the beginning 

of irrigation development, water levels were more 

than 70 feet below land surface. Changing much of the 

mesa from a desert area to a highly developed 

irrigated area resulted in the building of a large 

ground-water mound, the extent and thickness of 

which are shown in figure 12. By 1960 the mound 

contained about 1.3 million acre-feet of water in the 

United States alone.

Southward extension of the mound is curtailed by 

the barrier effect of the Algodones fault that probably 

exists at depth below the Yuma Mesa. The westward 

and northward extent of the mound was curtailed by 

pumping of drainage wells in the flood plain adjacent 

to the northern and western boundaries of the mesa. 

In the late 1950's, before the drainage wells were 

being pumped in the flood plain at the northern edge 

of the mesa, the apex of the mound was so near land 

surface that a tile drainage system was installed in a 

limited area near the apex to lower water levels to 

acceptable depths. Increased pumping of drainage 

wells in the flood plain adjacent to the western margin 

of the mesa and the pumping of newly constructed 

drainage wells adjacent to the northern margin of the 

mesa during the next decade lowered water levels in 

the higher parts of the mound sufficiently to cause the 

tile drainage system to become inoperative. Average 

annual pumpage from drainage wells increased from 

19,000 acre-feet during 1948-52 to 120,000 acre-feet
SUMMARY REPORT AS OF 1971

114°30'

A27

CALIFORNIA 

 MEXICO

Mountains and hills

Alluvial escarpment

Line of equal water-level rise, in feet 

Approximately located

A O-IL1 L

Dotted where concealed Q

Base from U.S. Geological Survey Hydrology by O. J. Loeltz

FIGURE 12. Change in water level beneath Yuma Mesa, 1925-66

during 1963-66. Had not these drainage wells been 

used to the extent that they were, large areas of the

adjacent flood-plain agricultural areas would have 

been waterlogged.
A28 WATER RESOURCES OF LOWER COLORADO RIVER - SALTON SEA AREA

GROUND-WATER MOVEMENT

The direction and the quantity of ground-water 

movement have been changed greatly in some areas 

because of developments by man. In most of the river 

valleys where irrigation with Colorado River water is 

extensive, water levels beneath the flood plain have 

risen above the levels that existed under virgin 

conditions. Generally, this rise of water levels has 

reduced the direct infiltration of river water that 

occurred under virgin conditions, but in some reaches, 

the rise has been sufficient to reverse the direction of 

the interflow between the river and the ground-water 

reservoir. For example, in the reach between Imperial 

Dam and the northerly international boundary, the 

river is now receiving water from the ground-water 

reservoir, whereas under virgin conditions the river 

was supplying water to the ground-water reservoir. 

Reversals of this type have also occurred in Palo 

Verde Valley and, to a lesser extent, in Parker Valley. 

On the other hand, man's activities have increased the 

infiltration rate from the river to the ground-water 

reservoir in some reaches. Probably the most 

noteworthy example is the Needles area, where 

infiltration from the river was increased by higher 

river stages that resulted from aggradation of the 

river channel upstream from Lake Havasu after 

completion of Parker Dam.

The water-level-contour maps of the principal areas 

indicate reaches where ground water is moving 

toward or away from the river. Further studies and 

additional data are needed if a more precise 

determination is to be made of where and at what 

rates interchange between ground water and the river 

occurs. Water-level contours in figure 13 indicate that 

the river probably is losing water throughout the 

reach north of Needles. Similarly, contours in figure 

14 indicate that some ground water probably is 

discharging to the river in the reach in the upper half 

of Parker Valley; however, in most of the rest of the 

reach in Parker Valley the river is losing water to the 

ground-water reservoir.

Water-level contours for Palo Verde Valley indicate 

that some of the river reaches, especially in the 

northern part of the valley, are receiving 

ground-water discharge. In the southern part of the 

valley, the relation between the river and the 

ground-water system is less clear. In Cibola Valley the 

river apparently is losing a considerable amount of 

water to areas east of the river.

Water-level contours for the delta region (fig. 15), 

which includes the Yuma area, indicate that ground 

water is discharging to the river upstream from the 

northerly international boundary. The average yearly

discharge to the river during 1960-63, on the basis of 

ground-water parameters, is estimated to be 72,000 

acre-feet. The contours also indicate westward movement of ground water from Yuma Valley. However, 

because of local conditions most of the ground water 

does not discharge into the river but continues to 

move westward into the Mexicali Valley. This outflow 

averaged 33,000 acre-ft/yr during 1960-63. Southward 

movement across the international boundary east of 

the river during 1960-63 is estimated to have been 

35,000 acre-ft/yr on the basis of the distribution of 

annual outflow from the ground-water mound beneath 

Yuma Mesa during the same period. Had the estimate 

been made on the basis of transmissivities and 

indicated hydraulic gradients, as was done for a 1970 

study, the estimated outflow would have been about 

6,000 acre-feet more. Readjustments of the other 

quantities of westward and northward outflow from 

the mound that would be required to keep the total 

outflow unchanged would not be unreasonable and 

would reduce the imbalance in the water budget for 

the Yuma Valley subarea. If estimates of outflow are 

to be used as a basis for comparison between the 

outflow during selected periods covered by the 

present study and outflows for future periods, the 

computations should be based solely on transmissivity 

and hydraulic gradients so that both values will have a 

common base.

The movement of ground water in Imperial Valley, 

as inferred from water-level contours (fig. 16), is 

generally westward and northwestward toward the 

Salton Sea. Much of the discharge, except that from 

the shallow deposits, is by upward leakage either to 

drains or to the lower reaches of the Alamo and New 

Rivers. A large part of the leakage from the 

Ail-American Canal, estimated at 150,000 acre-feet 

annually in 1961-63 for the 37-mile reach west of Pilot 

Knob, moves southward from the canal across the 

international boundary into Mexicali Valley. Prior to 

the construction of the canal, the rate of movement of 

ground water was much less, and the movement 

generally was parallel to the international boundary.

CHANGES IN THE HYDROLOGIC 

ENVIRONMENT

During the past 40 years the hydrologic 

environment of the lower Colorado River has been 

altered greatly by man in his attempts to utilize more 

fully the flow of the river. Consequently, during the 

10-year period of the lower Colorado River study, 

many changes occurred that necessitated a shift in 

emphasis on certain phases of the investigation.
114" 45'

SUMMARY REPORT AS OF 1971

114° 30'

A29

Generalized 

flood-plain 

boundary

Generalized 

flood-plain 

boundary

EXPLANATION

Water-level contour 

Shows altitude of water level, in feet. 

Dashed where approximately located. 

Contour interval is variable. Datum is 

mean sea level

5 MILES

I I T \ I

12345 KILOMETRES

Base from U.S. Geological Survey Hydrology by O. J. Loeltz

FIGURE 13. Generalized water-level contours during 1962-69 in Mohave Valley, Ariz.-Calif.-Nev.
A30 WATER RESOURCES OF LOWER COLORADO RIVER- SALTON SEA AREA

114° 45' 30' 114° 15'

flood-plain 

boundary

_

302

[298

Generalized 

flood-plain 

boundary

EXPLANATION

Water-level contour 

Shows altitude of water level, in feet. 

Dashed where approximately located 

Contour interval is variable. Datum 

is mean sea level

Irrigated land in Colorado 

River Indian Reservation, 1964

Base from U.S. Geological Survey 

Hydrology by O. J. Loeltz

FIGURE 14. Generalized water-level contours in Parker-Blythe-Cibola area, 1964.
115-15'

115°00

30'

32°45' -

32°15

Water-level contour

Shows altitude of water level. 

Dashed where approximately 

located. Contour interval 5 and 

lOfeet.Datum is mean sea level

Fault 

Dotted where concealed

FIGURE 15. Average water-level contours in the delta region in December 1965.
// 115°30' RIVERSIDE CO

115°00

EXPLANATION

Water-level contour 

Shows altitude of water level, in 

Dashed where approximately 

ed. Contour interval is variab

Datum is mean sea levej

WEST r

MESA\ l

5 10KILOMETRES

Hy

Base from U.S. Geological Survey

FIGURE 16. Water-level contours of main body of ground water in Imperial Valley, 1965
SUMMARY REPORT AS OF 1971 A33

A large increase in irrigated acreage in the Colorado 

River Indian Reservation in Parker Valley followed 

the change from short-term to long-term leasing of 

agricultural land. Development of the new land 

caused a marked increase in return flows and in the 

annual load of salt from Parker Valley to the Colorado 

River.

Many applications for acquiring land on the Palo 

Verde Mesa, west of Blythe, Calif., under terms of the 

Desert Land Act were filed during the investigation. 

The effects of pumping ground water for irrigation of 

these lands on the ground-water supplies in the flood 

plain east of the mesa and the long-term effects on the 

depletion of the Colorado River were questions that 

arose during the investigation.

Pumping of ground water for irrigation on the Yuma 

Mesa increased from virtually nothing in 1960 to about 

30,000 acre-feet in 1969. This pumping, by private 

citizens outside the irrigation district boundaries, 

utilized some of the recharge to the area that resulted 

from irrigating 20,000 acres of citrus with Colorado 

River water. A determination of the effects of this 

pumping and further planned developments on the 

ground water stored beneath the mesa and on the 

ground-water outflow from the mesa to Yuma Valley 

and across the international boundary into Mexico was 

a phase of the investigation that was not anticipated at 

the beginning of the project studies.

In the South Gila Valley in the Yuma area, Colorado 

River water was made available for irrigating some 

9,000 acres of land that until 1965 had been irrigated 

solely by pumping ground water. Pumpage from 

drainage wells, sumps, and drains adjacent to the 

Yuma Mesa increased from about 70,000 acre-feet in 

1960 to 146,000 acre-feet in 1969. The disposal of this 

drainage water and an additional 200,000 acre-feet of 

moderately saline (4,000-6,000 mg/1) pumped return 

flow from the Wellton-Mohawk area beginning in 1961 

necessitated a much more careful monitoring of these 

flows and their salinities to permit their disposal in a 

manner satisfactory, on a temporary basis, to 

interests in both the United States and Mexico.

Pumpage for irrigation in Mexicali Valley increased 

from about 700,000 acre-feet in 1960 to almost 1 

million acre-feet near the end of the decade. This 

increase in pumpage, in addition to the increase from 

about 300,000 acre-feet in 1956 to the 700,000 acre-feet 

in 1960 steepened the hydraulic gradients across the 

limitrophe (international boundary) section of the 

river. As a consequence, extensive studies, which 

included the use of the electric analog model of the 

Yuma area, were made to determine the overall 

effects of the pumping in Mexicali Valley on the flow of 

ground water across the international boundary.

The filling of newly created Lake Powell during the 

project resulted in changes in the surface-water 

regimen of the river and also affected the chemical 

quality of the river downstream from the lake.

Other changes in regimen resulted from the 

large-scale channel-improvement program of the U.S. 

Bureau of Reclamation. Improvement of channel 

geometry, alinement, and dredging operations were 

completed for several reaches in the project area. 

Some of the realinement and dredging operations 

resulted in significant changes in the relation between 

the river and the ground-water reservoir.

CONTINUING PROBLEMS AND 

PROPOSED INVESTIGATIONS

Distribution of the available supply of Colorado 

River water in an equitable manner to all parties 

dependent on that water will always pose some 

problems. These distributions are intrastate, 

interstate, and international and will become more 

difficult as the increasing demands for water equal and 

eventually exceed the available supply.

In recent years major interests in all the basin 

States have been coming to the conclusion that the 

solution of the water-supply problems of the 

Southwest requires a regional approach. Accordingly, 

in 1965 the governors of 11 western States directed 

the organization of the Western States Water Council, 

comprising representatives of the 7 Colorado River 

basin States and the 4 Pacific Northwest States, to 

seek the solution of water problems on a West-States 

basis.

Further recognition of the need for a regional 

approach was the passage by Congress and the signing 

into law by the President on September 30, 1968, the 

Colorado River Basin Project Act (Public Law 90-537), 

the major features of which are 

1. The Central Arizona Project and several Upper 

Colorado River Basin projects are authorized for 

construction and the Dixie Project in southern Utah 

is reauthorized.

2. Existing Arizona, California, and Nevada contractors for water receive a priority of deliveries over 

the Central Arizona Project.

3. The United States assumes the responsibility of 

meeting the Mexican Treaty water deliveries when 

the flow of the river is augmented by 2.5 million 

acre-feet or more of water per year.

4. The Secretary of the Interior is to study water 

supply and requirements and develop a plan for
A34 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA

meeting the water needs of the West, but any study 

for importing water from any other natural river 

drainage basin to the Colorado River basin must be 

delayed 10 years.

5. A basin fund is established to help repay future 

augmentation costs.

6. Priorities are established for the operation of the 

major Colorado River reservoirs.

Adequate augmentation of the water supply from 

sources outside the basin, however, could not become 

a reality for several decades even if such a decision 

were finally made. First, it would be necessary to 

achieve region wide concurrence of its desirability; and 

second, many years would be required to obtain the 

necessary authorization, to arrange adequate 

financing, and to design and construct the extensive 

facilities that would be needed.

Methods for augmenting the freshwater supply 

other than by importing fresh water are in limited use 

or being investigated. Weather modification, 

specifically cloud seeding to increase precipitation in a 

given area at a given time, is being used successfully 

in more areas and with greater frequency than was 

true just a few years ago. Studies are being made by 

the University of California at Riverside to determine 

if ground water can be desalinized in conjunction with 

the development of the geothermal resources of 

Imperial Valley. Initial studies at the University of 

Arizona suggests that the capture of solar energy as a 

heat source for generating electricity by means of 

steam turbines may be economically feasible. If so, the 

solar energy falling on the vast expanse of desert in 

the lower Colorado River valley would be sufficient to 

generate enough power to meet the needs of the entire 

Southwest for the foreseeable future and also to 

desalinize tens of'millions of acre-feet of sea water 

annually. These possibilities need to be studied 

further.

In the meantime, present measures should be 

continued and new measures undertaken for reducing 

insofar as is economically feasible unnecessary losses 

and waste of the present supply.

SELECTED REFERENCES

Blaney, H.F., and Harris, Karl, 1952, Consumptive use of water 

rates in the lower Colorado River basin (provisional), in Report 

on water supply of the lower Colorado River basin Project 

planning report: Boulder City, Nev., U.S. Bur. Reclamation, 

427 p.

Erie, L.J., French, O.F., and Harris, Karl, 1965, Consumptive use 

of water by crops in Arizona: Tucson, Ariz., Univ. Arizona 

Agricultural Exp. Sta., U.S. Dept. Agriculture Tech. Bull. 

169, 44p.

Hely, A.G., and Peck, E.L., 1964, Precipitation, runoff, and water 

loss in the lower Colorado River-Salton Sea area: U.S. Geol. 

Survey Prof. Paper 486-B, 16 p.

Hely, A.G., Hughes, G.H., and Irelan, Burdge, 1966, Hydrologic 

regimen of Salton Sea, California: U.S. Geol. Survey Prof. 

Paper 486-C, 32 p.

Hely, A.G., 1969, Lower Colorado River water supply Its magnitude and distribution: U.S. Geol. Survey Prof. Paper 486-D, 

54 p.

lorns, W.V., Hembree, C.H., and Oakland, G.L., 1965, Water resources of the Upper Colorado River Basin Technical report: 

U.S. Geol. Survey Prof. Paper 441, 370 p.

Irelan, Burdge, 1971, Salinity of surface water in the lower 

Colorado River-Salton Sea area: U.S. Geol. Survey Prof. 

Paper 486-E, 40 p.

Loeltz, O.J., and McDonald, C.C., 1969, Water loss in the lower 

Colorado River valley, Davis Dam to Imperial Dam: Am. Soc. 

Civil Engineers, v. 95, no. IR 1, Proc. Paper 6457, p. 65-78.

Loeltz, O.J., Robison, J.H., Irelan, Burdge, and Olmsted, F.H., 

1975, Geohydrologic reconnaissance of the Imperial Valley, 

California: U.S. Geol. Survey Prof. Paper 486-K, 54 p.

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water by phreatophytes and hydrophytes near Yuma, 

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