ARIZONA 

WATER

By J. W. Harshbarger, D. D. Lewis, H. E. Sldbitzke,

W. L. Heckler, and L. R. Kister,

revised by H. L. Baldwin

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1648

U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON: 1966
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

WILLIAM T. PECORA, Director

Library of Congress catalog-card No. GS 65-412

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

Office, Washington, B.C., 20402.

II
CONTENTS

The Vanished Ones ..... 1

The Problems ..... 4

evaporation . . 4 

scarcity of usable water ... 5 

ground-water depletion ..... 7 

salts in the soil ..... 11

The Past ..... 14

growth of water development ..... 14 

the Colorado River ..... 23

The Present ..... 26

water resources ..... 26

use of water ..... 57

some results of present use ..... 70

The Future ..... 72

For More Information ..... 81

m
FIGURES

Page

1. The three major regions .................. 3

2. The natural cycle of water................. 6

3. Water-bearing rock strata. ................. 7

4. Ground-water movement in desert basins..... 9

5. Water table in Salt River Valley ............ 17

6. Water table in the lower Santa Cruz basin ... 21

7. The Central Highlands region .............. 28

8. Average annual precipitation ............... 30

9. Annual discharge of streams ............ . :. 31

10. History of ground and surface water in Salt

River Valley ........................... 34

11. Average loads of dissolved salts in streams .... 39

12. Geology of the Plateau Uplands region ...... 41

13. Discharge of springs, Grand Canyon area. .... 42

14. Rock formations in Navajo country ......... 45

15. Analyses of representative ground waters, Pla- 

	teau Uplands region..................... 47

16. Average loads of suspended sediment in streams

	on the Plateau Uplands ................. 49

17. Disposition of water during a flood .......... 52

18. Geology of the Desert Lowlands region. ...... 54

19. Alluvial basins in central Arizona ........... 56

20. Use of water ............................. 58

21. Ground-water pumpage for irrigation in 1963. . 59

22. Using wells for artificial recharge ........... 77

rv
this report was written

Water is a scarce commodity in Arizona, as it is in all semiarid 

lands. Therefore all possible information about it should be 

acquired and effectively used for the best interests of all. Man has 

made great strides in learning how to live in the desert. However, the basic problem still exists a shortage of usable water 

to meet the needs of a rapidly growing economy. This report is 

an effort to help those interested to understand the problem. It 

discusses the water resources of the State, the current use of this 

resource, and some methods of relieving the present shortag'e and 

avoiding a future shortage.

The report is written in nontechnical terms. Statements about 

amounts of water and other quantitative information are generalized. The information presented here is neither in the form 

nor in the detail required for engineering and legal purposes. 

Although the figures are derived principally from publications of 

the Geological Survey, the specialist will want to consult those 

publications and other sources for technical data.

For many people the word "Arizona" may conjure up a picture of a desert full of thorny trees, brush, and cactus. At the 

same time, thoughts of modern Phoenix and Tucson come to 

mind dramatic skyscrapers designed by leading contemporary 

architects, luxurious hotels and motels, modern houses with patios 

and swimming pools. How has this prosperous way of life been 

achieved in the midst of what we call a desert?

When we think of a desert we often picture acres of windblown 

sand in the sun, stretching for miles and miles without trees, plants, 

or flowers. This is often far from a true picture of the Arizona 

deserts, which after a wet winter may be lush with flowers of 

every color. Scientists define a desert as a region of sparse vegetation found in areas of low rainfall. Even by this definition, 

Arizona is far from being wholly a desert.

There are three basic geographic regions in Arizona Desert 

Lowlands, Central Highlands, and Plateau Uplands (fig. 1). Two 

of these, the desert and plateau, have very little rainfall. More

1
than 95 percent of what rainfall there is evaporates very rapidly 

because of the hot dry climate. More rain falls in the mountains, 

but unfortunately man cannot live or farm very well on steep 

slopes. In reality, a good deal of Arizona is arid to semiarid.

Yet civilizations have flourished here. Prehistoric man first 

came to Arizona between 12,000 and 15,000 years ago, but the 

earliest culture we know much about dates from about 800 B.C. 

The Hohokam, who flourished from the beginning of the Christian 

era to about A.D. 1400, is the most interesting of these ancient 

cultures because it partly solved the primary problem of Arizona how to use and manage the scant supply of water to the 

best advantage. The word "hohokam" means the vanished ones. 

These people built irrigation canals that diverted water from the 

rivers and delivered it to the thirsty fields. Several hundred miles 

of these < anals can still be traced a great achievement by any 

standards, but an extraordinary one for Indians working with 

primitive tools. Some of the present-day irrigation canals follow the same courses used by the Indians. The Hohokam grew 

corn, beans, squash, and cotton. The food surplus produced by 

irrigation allowed for leisure and the arts of civilization ball 

games, textile and pottery-making, sculpture. The Hohokam 

civilization was the model and inspiration for neighboring tribes. 

Their achievements demonstrate man's capacity to meet the challenge of a difficult environment, and to manage natural resources 

wisely.

At some point, however, the Hohokam civilization vanished; 

how or why we do not know, but most authorities think it was 

because of a great drought that lasted for several years. Since 

their irrigation system lacked storage reservoirs, the Hohokam 

were at a loss to deal with this blow to their way of life, and their 

civilization faded, leaving the canals behind as inspiration to those 

who followed.

The first white settlers, too, adjusted their life and economy to 

the semiarid environment. In 1867, Jack Swilling organized 

the first "Ditch Company." The canals of this company and 

of others led the water out on to the fertile flood plain of the 

Salt River, and the country prospered at least until the severe 

droughts of 1897, 1898, and 1899. Again, the lack of water 

storage proved a weakness in an otherwise excellent irrigation 

system.
Figure 1. The three major regions of Arizona.

It remained for modern Arizonians to remedy the defect by 

building dams and reservoirs. They have produced magnificent 

cities and resorts and great wealth in spite of what once were considered disadvantages the scarcity of water and the hot dry 

climate. Water is the problem of living in Arizona, but water 

in swimming pools and air-conditioners is also the secret of successful adaptation to the climate. The story of Arizona water is 

the story of man's continuing effort to master the complicated 

secrets of nature and turn them to beneficial use.
THE PROBLEM:

Evaporation

The "gold" in Arizona's hills is sunshine, the State's greatest 

natural resource. Health-conscious and sports-loving Americans 

crave sunshine, and they will spend a great deal of money to get 

enough of it. They will even create a lavish civilization in a 

desert for the sake of endless sunshine and the climate of Arizona 

is phenomenally sunny. The amount of possible annual sunshine throughout the State ranges from 73 to 90 percent. The 

average for the State is a startling 80 percent. The humidity is 

generally very low and there is little wind. To people from other 

States, this perpetual summer may mean merely a winter tan, or 

it may mean outdoor living all year round and relief from a lifelong plague of asthma or sinusitis.

But the sun, which blesses Arizona with its light and warmth 

on the one hand, steals away its water on the other. Anyone driving or flying over the State can see that it is dry. Yet in an average year, the State receives 80 million acre-feet of water from rain
and snow. An acre-foot is the amount of water which would 

cover 1 acre to a depth of 1 foot (326,000 gallons). That is a lot 

of water! The great rivers the Colorado, the Gila, the Salt, and 

the Verde also add much water to this large amount.

Why shouldn't there be enough water?

The answer lies in one astounding statistic. Of the 80 million 

acre-feet of water available from precipitation, only a shockingly 

low 2 million is captured for man's use.

More than 95 percent of the precipitation falling on Arizona 

is consumed by evaporation and by transpiration (the process 

by which plants breathe water into the atmosphere). For the 

United States as a whole, the percentage of loss in this way is 

about 70.

The high rate of evaporation in the arid Southwest is strikingly 

shown by a study of evaporation from Lake Mead during 1957. 

The evaporation loss rate was about 90 inches per year from 

this reservoir surface. The volume of water evaporated was 

about 800,000 acre-feet. Evaporation from other reservoirs on 

the Colorado River, from the channel of the river itself, and from 

reservoirs within Arizona, amounts to more than 500,000 acrefeet per year.

The total water loss from all reservoirs, though great enough, is 

small compared with the total evaporation from all the land surface. Rainwater from the sudden storms of summer does not penetrate deeply into the soil. Some of the soil moisture is taken up by 

plant roots, but most evaporates shortly after a storm. Even 

when the rain is heavy enough to cause some runoff (water which 

runs over the surface of the land into streams), part of this water 

sinks into streambeds. After the storm ends, much of the water 

retained in the river channel evaporates or is transpired by riverbank vegetation.

Scarcity of usable water

The high percentage of evaporation causes a scarcity of water 

available for use by man. Presently, Arizona uses about 7 million acre-feet of water annually, of which about 2 million is from 

surface water and about 5 million is pumped from the ground. 

Hydrologists estimate that of the total 7 million acre-feet not
more than 3 million is from the renewable supply of surface and 

ground water. The remaining 4 million acre-feet represents 

withdrawal of ground water from storage in excess of 

replenishment.

Demand for water is greatest in the arid valleys in the south, 

where it is used for light industry and municipal supply as well 

as for agriculture. Increasing present demands for water are 

many water-consuming devices, including the all-important air 

conditioning, which has made the desert a more comfortable 

place to live. If growth continues at the present rate or at a 

higher rate, much more water will be needed.

Census Bureau statistics show that the population of the West 

is growing extremely fast, and Arizona is one of the leaders in 

this growth. Their figures also show that Arizona is rapidly becoming more urban and industrialized. Nearly 50 percent of all 

the people in Arizona live in Phoenix or its suburbs, about 25 percent more live in the Tucson area, and the remaining 25 percent 

are scattered throughout the State. The expanding urban centers are competing more and more with farms for the use of land 

and water. This trend may continue, and as water rights are 

acquired by users who can pay the price, more land may be withdrawn from agriculture and put to urban use. Whether it 

is used to supply farms, homes, or industries, more and more

Figure 2. The natural cycle of water.

GROUND WATER
Area of recharge for aquifer

Outcrop area of 

bed overlying 

aquifer

Aquifer

Figure.3. Water-bearing rock strata, or aquifer, underground and at the 

earth's surface.

ground water is being used, because of the basic water problem 

a shortage of usable water that cannot be furnished by existing 

surface-water supplies.

Ground-water depletion

Water evaporates from the land and ocean and is carried as 

vapor or clouds in the air. Then somewhere it falls as rain or 

snow, returning to the land or the sea to go through the same 

wonderful natural cycle all over again (fig. 2). Water from 

rainfall on any area departs in one of three ways: through the 

atmosphere as water vapor, as runoff in stream channels, or as 

ground water. Ground water is all the water clinging to and 

saturating the rock some distance below the soil surface.

Rainfall enters the ground and starts downward. How this 

moisture moves through the soil is not fully understood. There 

is growing evidence that much more of it is returned to the surface, 

to be evaporated or used by plants, than is commonly believed. 

When rainfall persists for a long time, however, water may percolate downward and penetrate to the water table and become 

ground water. Ground water occurs in water-bearing strata of 

rock called aquifers (fig. 3). The aquifers are replenished, or
recharged, by precipitation where they are at or close to the surface. This recharge area may be many miles from the place where 

the ground water emerges as a spring or is pumped from a well.

Streams that flow over permeable soils above the water table 

lose water by seepage into the ground, and this tends to build up 

ground-water levels. One might say the stream channel has a 

"leaky" bottom. On the other hand, where the water table is 

higher than the stream channel, ground water flows into the 

river. This is called the base flow of a river. Surface streams 

and ground water are thus connected and form a part of a single 

hydrologic system. Since streams and ground water are parts 

of a single system, excessive withdrawal of either one will diminish the other, and heavy pumping in certain areas in Arizona has 

caused some streams to stop flowing.

Ground water moves very slowly. The total amount of water 

in underground storage may be very large, but in a highly developed area the volume of flow is usually less than the amount 

being withdrawn by pumping. The lowering of the water table 

may be noticeable at distant places only after a long time. The 

water user's experience, however, may lead him to look upon a 

ground-water reservoir as an "inexhaustible lake." The groundwater reservoir is not a lake; nor is it inexhaustible, unfortunately. 

Although it will take many years to realize the full effects of current withdrawals of ground water, it is entirely possible to exhaust 

the supply eventually.

Withdrawal of water from storage underground is quite different from withdrawal of water from a surface reservoir. Water 

in a surface reservoir moves readily toward the pump, and the 

lake surface remains nearly level. But underground water moves 

very slowly toward a pumped well, and the surface slope of the 

water table steepens toward the well. Thus pumping creates a 

cone of depression in the water table (fig. 4). The area of depression and shape of the cone depend on the permeability of the 

water-bearing formation and the rate of pumping. Cones spread 

outward continually as pumping continues. Theoretically, the 

cone around a well continually pumped will ultimately lower the 

water level in all parts of a basin, but in a large basin the final 

effect would not be achieved for a long time. Where many wells 

are pumped, the water table is pitted with cones of depression.

8
Well

Ground surface

Ground-water movement before pumping

Ground

Ground-water movement neor a pumping we

Ground surface Pumped wells

Regional depression of water table after prolonged pumping by many wells

Figure 4. Ground-water movement fn desert basins.
These generally combine to form one very large total cone of 

depression.

HOY/ long can one pump at a given rate? This depends on 

the amount of water in storage, which is fixed, and the amount 

of replenishment, which varies. One can choose between pumping at whatever rate is desired until all the recoverable water is 

gone, or pumping at a rate that will assure a continuous supply 

for some chosen length of time.

There is one important difference between taking water from 

a stream and taking it from a lake or ground-water reservoir. 

The rate at which water can be withdrawn from a stream cannot exceed the flow in the stream, whereas water may be pumped 

from a lake or underground reservoir at almost any desired rate. 

The length of time that pumping can continue before the store's 

reserve is gone depends on how fast we pump. Most geologists 

and hydrologists who have studied ground water in Arizona believe that the amount of replenishment of the underground reservoirs in the heavily pumped areas is many times less than the 

amount being withdrawn.

Contrast between irrigated and nonirrigated lands.
Arizona's desert basins contain no lakes; so the water in groundwater reservoirs is the only naturally stored reserve. The groundwater reservoir once stored a volume of ground water roughly 

equal to the volume of water in Lake Michigan (about 4^2 billion acre-feet). Perhaps about 15 percent (700 million acrefeet) of this original volume of water was economically recoverable for use by man, of which about 10 percent (100 million) 

has been withdrawn, most of it in the last 25 years. Although 

this is only a small part of the total, it is the most easily and 

cheaply available part. In ground-water economy, readily available storage is more important than total storage.

Before man arrived on the scene, the water system in the basins 

of Arizona was in hydrologic balance inflow equaled outflow. 

In any given area, inflow includes the total rainfall and the water 

entering the area by way of streams or by ground-water underflow. Outflow includes water leaving the area as streamflow and 

as ground-water seepage, and it also includes evapotranspiration 

loss. Man subtracts the water he uses from some part of this 

natural system. In doing so, he may draw on the reserves accumulated in ground-water storage. Under man's regime, therefore, outflow may exceed inflow (while storage lasts), and it actually does so in many areas in Arizona.

Salts in the soil

A problem that has received serious attention only recently is 

the effect of use on the quality of water. Nearly all use of water 

results in deterioration in the physical or chemical quality of the 

water when it is returned to the ground or to streams.

The chemical nature of water changes constantly as the water 

moves through its natural cycle, passing from vapor to cloud to 

rain or snow, to rivers and underground flow to lakes and oceans, 

then back into the atmosphere again as vapor (fig. 2). Rain and 

snow contain gases such as carbon dioxide, oxygen, and nitrogen 

and may carry small amounts of chloride, sulfate, and nitrate. 

The gases in rainwater help to dissolve many minerals as the 

water flows over the ground or percolates slowly through the 

rocks beneath the surface. The dissolved minerals in water commonly are called salts. This term is used in a chemical sense, 

however; it does not imply that all these minerals are salt in the 

ordinary sense, such as table salt (sodium chloride).

681-100 O-66 2 11
Irrigation invariably results in concentration of dissolved mineral matter, or salts, in the return water, because the plants consume a large part of the water applied but only a small part of 

the salts. Also, mineral fertilizers and soil minerals are carried 

off in solution in the return water. On heavy soils from which 

water drains slowly, the moist soil loses much water to evaporation, 

and this concentrates the salts even more.

In such situations mineral concentrations in the soil may be as 

much as 100 times the concentrations in the water applied. These 

high mineral concentrations retard or prevent plant growth. Unless soils are well drained and receive sufficient excess water to 

flush out the salts, irrigation always increases soil salinity. Eventually the soil may become too highly mineralized for further use.

Soil-salinity problems are rare in areas where rainfall is sufficient to grow crop.^, without irrigation, because the natural water 

supply flushes the soil. Saline soil is common in the West and 

Southwest, however, and irrigation increases the problem.

Two methods of meeting the problem have been used. One 

is to ignore salinity and wring as much profit from the land as 

possible before abandoning it. The other approach is to make 

full use of available knowledge and seek more on the interrelations of soil chemistry, water chemistry, plant physiology, and 

soil rehabilitation. Soil and water experts are working hard on 

these problems, for the problem is already acute.

For many years more mineral matter has entered the Salt River 

Valley in the surface-water supply than leaves the area in the 

outflow. This unfavorable "salt balance" results in a gradual 

increase in the mineral content of the ground water and deterioration of the quality of the surface outflow. A progressive increase 

in the dissolved mineral content of the ground-water supplies has 

been observed for several years in the area between Tolleson and 

Gillespie Dam. With the beginning of large-scale pumping in 

the Wellton-Mohawk project area to lower the excessively high 

water table, water of poor quality with high dissolved-solids content has been delivered to the Colorado River during the winter 

periods of low flow. The water users in Mexico have claimed 

over a period of time that their supply was not suitable for irrigation and the Mexican Government asked for relief. The matter 

has been under consideration by both Governments, and it is

12
expected that a satisfactory method of handling the problem will 

be worked out.

All these water problems in Arizona are inextricably interconnected and are based on the fundamental facts of weather and 

climate. Over much of Arizona, precipitation is light and evaporation is high. The scarcity of usable surface water results in 

depletion of the ground-water reserve. Intensive irrigation is necessary to support a predominantly agricultural economy, and in 

its turn produces excessive soil salinity.

Climate cannot as yet be changed. Can man change the way 

he manages the water?

Let us look into the past history of water development in Arizona to see how the present situation arose.

Irrigation canal in the Wellton-Mohawk division of the Gila project.

13
THE 

PAST

Growth of water development

As in most parts of the country, early water development in 

Arizona was rather sporadic. But irrigation in Arizona antedates 

white settlement; as we have said, the Indians irrigated Arizona 

land more than a thousand years ago. About 125 miles of prehistoric irrigation canals has been found in the Salt River Valley 

and in the Gila River valley.

The most enterprising irrigation project of the prehistoric 

Indians of Arizona was in the Salt River Valley, in a flat fertile 

area some 15 miles wide and 45 miles long, near the present location of Phoenix. The good soil in this valley, the perennial surface 

water flowing from the mountains, and the ample sunshine made 

it a logical place for both prehistoric and modern settlements.

Archeologists say that the Salt River Valley was irrigated as 

early as A.D. 800. The Indians dug wells to tap shallow ground 

water, but they relied mostly on rainfall and natural streamflow. 

Their canal system was identified by surveyors and confirmed in 

1929 by aerial survey. The main canals were as wide as 60 feet 

and could carry enough water to irrigate 250,000 acres, but 

probably not all the area was irrigated at any one time. Beans, 

squash, corn, tobacco, and probably cotton were grown.

14
The Hohokam lived in the southwestern Arizona desert for 

more than a thousand years. Why they disappeared, or lost their 

identity as a people, is not known. Archeologists and geologists 

have their theories, but at present there is no way of establishing 

precisely what happened. Experts say that the local tree-rings 

indicate a great drought that lasted on and off through most of 

the 13th century. The persistence of such a drought might have 

caused a gradual exodus of the Hohokam people. At the same 

time, because of the drought, the farmers perhaps irrigated even 

more intensively than usual. Possibly the land became waterlogged, a condition as bad for crops as too little water. Or perhaps, after centuries of use, the land was simply exhausted and 

laden with salts left by evaporation of the irrigation water. Any 

one of these conditions, or a combination of them all, might have 

led to the degeneration of the Hohokam as a cultural entity.

Although we do not know exactly why they vanished, their disappearance probably had something to do with their water and 

land problems. They responded to the challenge of their environment with intelligence and imagination. Had they been able to 

construct storage reservoirs, their culture might have lasted until 

the Spanish came.

As it is, little is known about human history in the Southwest 

between 1400 and the arrival of the Spanish explorers. After 

the Spanish, came settlers of English descent. They began to irrigate about 1867, and by 1878 more than 200,000 acres was 

cultivated. Many of these canals followed the same courses used 

by the Indians. The drought of 1897-99 forced more than 

75,000 acres out of cultivation. By the time Congress passed 

the Federal Reclamation Act on June 17, 1902, approximately 

126,000 acres was under cultivation.

As in any arid land, the development of Arizona was intimately 

connected with available water supplies. Shortly after the Civil 

War, pioneers settled along the Gila River, in the Florence area, 

where water was readily available. Picacho Reservoir, the first 

of many for storage of irrigation water, was built in 1890 in the 

Casa Grande Florence area. By the 1930's it was shown that 

large amounts of water could be obtained from natural underground storage, and agriculture using water from wells expanded 

rapidly after World War II.

15
Diversion dams in southern Arizona.

To assure a constant supply of water for the irrigated land, 

storage in reservoirs behind dams was necessary. How to finance 

such facilities was a general problem in the West until the Reclamation Act opened the way for appropriations of money for 

surveys, planning, and construction. In order to transact business in connection with dam-building, the Salt River Valley 

Water Users' Association, the first organization of its kind formed 

to take advantage of the act, was incorporated in February 1903.

Construction of Roosevelt Dam on the Salt River was begun 

in 1905 and completed in 1911. Two hundred and eighty feet 

high, it was at that time the highest dam in the world. The dam 

provided a stable source of water for irrigation, as well as for 

power generation. Granite Reef diversion dam was built on the 

Salt River below the mouth of the Verde to divert water from the 

Salt River into the canal system.

By 1920 Roosevelt Lake had overflowed four times, and much 

valuable water had flowed unused out of the area. In order to 

conserve more water, the Water Users' financed and built three 

additional dams on the Salt River below Roosevelt: Mormon Flat 

(Canyon Lake) in 1923-25; Horse Mesa (Apache Lake) in 

1924-27; and Stewart Mountain Dam (Sahuaro Lake) in 1928- 

30. The combined capacity of the four reservoirs is about 1,750,- 

000 acre-feet, and their spillways are designed to pass a flood of 

150,000 cfs (cubic feet per second;. Since 1920, this system has 

overflowed only once, from April to July 1941.

16
Irrigation has greatly affected the ground-water situation in 

the Salt River Valley. Under natural conditions ground-water 

levels in the Phoenix area were controlled by a rock barrier under 

the channel of the Salt River at Tempe Narrows. This barrier 

impounded the ground water; the water table was at the surface 

along the stream channel; and the ground water discharged into 

the stream channel. Farther up the valley and along the mountain fronts the water table was deeper. For example, near the 

Superstition Mountains it was more than 500 feet below the land 

surface.

In the early 1900's these natural hydrologic conditions were 

modified. Irrigation water from streams was spread over the 

land between the mountain fronts and the river. Much of the 

water entered the ground, recharged the ground-water reservoir, 

and caused the water table to rise. Because little or no water was 

pumped from the ground-water reservoir, water levels rose steadily 

until about 1924 (fig. 5) and farming became difficult because 

the soil was waterlogged. Drainage wells had to be drilled and 

pumped to lower the water table.

At first, the drainage water was wasted, but later it was used 

for supplemental irrigation. In 1929, the Roosevelt Irrigation 

District built canals and aqueducts to carry off this pumped water, 

delivering it to lands to the west, where the ground water is poor

Sierra Estrella

Figure 5. Water table in Salt River Valley.

17
in quality and no surface water is available. The district also 

drilled wells along the 30-mile canal and exported water from 

these wells.

Nowadays, people who live in the vicinity of Phoenix are concerned about this exportation of water because water levels in 

wells are declining rapidly. Before 1940, irrigation with surface 

water had caused the water table to rise also in Deer Valley, in 

lower Paradise Valley, and in the area east of the Roosevelt Water 

Conservation District. About 1940, however, the cultivated area 

in the Salt River Valley expanded beyond the region irrigated 

with surface water, and irrigation water began to be pumped 

from wells. Thereafter, water levels declined, and in recent years 

the water table has dropped far below its original level.

During the drought in the forties, additional ground water 

was pumped to make up shortages in the surface water in the 

Salt River Valley. After World War II, high prices for farm 

products stimulated irrigation and increased the demand for 

water. Today, all available surface-water supplies are in use, 

and the ground-water reserve is being intensively developed.

Irrigation is practiced in other valleys of Arizona, and other 

storage dams have been built. Lake Pleasant Dam, the oldest 

storage facility on the Agua Fria River, was built in 1927 to furnish 

irrigation water for 50,000 acres in Maricopa County Municipal 

Water Conservation District No. 1. The storage capacity of 

the reservoir is 160,000 acre-feet, and the reservoir has overflowed only once, in 1941.

The earliest irrigation in the lower Gila River valley after that 

by the Indians was started by settlers in the Florence District in 

1864. By 1867, 12 canals were delivering water to irrigate 

6,000 acres. Settlers began irrigating in the Safford area in 

1872 and in the Duncan area in 1879. The Buckeye Canal, on 

the north side of the Gila about 4 miles below the mouth of the 

Salt River, began delivery of water in 1888. By 1905 some 

29,000 acres was irrigated in the Gila River valley.

Coolidge Dam was built in 1928 to store floodwater. Its lake, 

known as San Carlos Reservoir, has a capacity of 1,200,000 

acre-feet, but the maximum storage attained thus far was 

819,200 acre-feet, in 1942. The reservoir has been empty 

several times.

18
Gillespie Dam, a diversion structure for the Gillespie Land 

and Irrigation Co., was completed in 1921 to irrigate 10,000 acres 

in the vicinity of Gila Bend and Theba. Lack of water has 

prevented complete development of the irrigation project.

The oldest storage dam on the upper Little Colorado River 

wa- built in 1913 but was washed out by a flood in August 1915. 

Lyman Dam, built in 1920 to serve the St. Johns area, has a 

reservoir capacity of 30,600 acre-feet and has overflowed only 

twice, in 1932 and in 1941. Upper and Lower Lake Mary on 

Walnut Creek, which have a combined capacity of about 35,000 

acre-feet, store water for municipal use at Flagstaff.

Yuma Valley has one of the oldest water rights on the Colorado 

River and uses this river water for irrigating more than 50,000 

acres on the flood plain today. By 1904 more than 10,000 acrefeet of water, diverted from the river by pumps and gravity, was 

used for irrigation. The supply depended, however, on unregulated river flow.

The Yuma Mesa auxiliary project was authorized by the congressional act of January 25, 1917; and work on the Mesa 

division, which became part of the Gila project, began in June 

1936. Water diverted at Imperial Dam now flows about 20 

miles by gravity through the Gila main canal to a pumping plant, 

which was completed in October 1941. The project includes 

delivery of water to the North Gila division and to the Wellt< nMohawk area, some 50 miles east of Yuma. By 1958, 60,000 

acres in the project was being irrigated with Colorado River 

water. More than 10,000 additional acres is supplied with 

ground water. Currently, more than a million acre-feet of water 

is diverted annually from the Colorado River to irrigate more 

than 125,000 acres near Yuma.

Citrus trees under irrigation, Yuma project.
River water applied to the porous soils of Yuma Mesa contributes to ground-water recharge and has created a unique 

situation in Arizona a surplus of ground water. Ground-water 

overflow from the mesa area has contributed to drainage problems 

in Yuma Valley. The degree to which mesa irrigation and 

valley irrigation are respectively responsible for the high water 

table in the Yuma Valley is difficult to determine.

The story of water development in the lower Santa Cruz 

basin is the story of agricultural development on a broad plain 

surrounded by mountains. The basin's main drainageway is 

the Santa Cruz River, which joins the Gila in Final County, 

southwest of Phoenix. For simplicity, the lower Santa Cruz is 

divided into four areas: Eloy, Maricopa-Stanfield, Avra-Marana, 

and Casa Grande-Florence.

Indians and early settlers in the Eloy area used floodwaters 

for irrigation, and the oldest irrigation wells were constructed 

in 1914. Many of these wells were abandoned, owing to the 

high cost of pumping. Then rapid expansion occurred in 1936 

and 1937, when cotton prices advanced and low-cost electricity 

became available for pumping. Some 40 to 50 wells were drilled 

during this period to irrigate about 18,000 acres of land. By 

1963 about 400 wells were in use, furnishing ground water to 

75,000 acres.

Modern Indians irrigated part of the Maricopa-Stanfield area 

with floodwater from the Santa Cruz River. Development of 

ground water began about 1920 and by 1935 about a dozen 

wells were pumped to irrigate some 2,000 acres. By 1941, 25,000 

acres was irrigated and the number of wells rose to 85. In 1963 

about 500 wells furnished water for more than 100,000 acres.

Indians used floodwaters for irrigation in the Avra-Marana 

area long before Arizona became a State. By 1935, however, 

irrigation had practically ceased because the canals and laterals 

had been cut so deep by erosion that they could not deliver the 

water to the surface of the land, and the equipment then available could not lift ground water economically. Ground water 

was developed in the Avra-Marana area later than in other areas. 

In the 1950's, rising prices for farm products made the lifting of 

ground water from greater depths economically feasible. In 

1963 some 40,000 acres was under irrigation with ground water 

pumped from depths as great as 300 feet.

20
The Casa Grande-Florence area differs from the Eloy and 

Avra-Marana areas in that surface water is available during 

part of the year. The Pima Indians have lived here since prehistoric times, and early settlers found them irrigating their land 

with Gila River water. From 1872 to 1930, because others 

were irrigating upstream near Florence, the water supply in the 

Casa Grande Florence area was inadequate and cultivation of 

downstream land dwindled. Wells were drilled in 1915 to obtain 

supplemental ground water. The number of wells in use was 

about 80 in 1939, nearly 300 in 1942, and more than 500 in 

1963.

Several small surface reservoirs and dams have been built in 

the Casa Grande Florence area. Picacho Reservoir was constructed by landowners in 1890 and was enlarged in 1956. Water 

from the Gila River is diverted into this reservoir through an 

18-mile canal. Storm runoff from the Picacho Mountains is 

also captured. Water from this reservoir is used in the vicinity 

of Casa Grande.

Figure 6. Water table in the lower Santa Cruz basin.

Northeast

Southwest

SAWTOOTH MOUNTAINS

PICACHO MOUNTAINS

Altitude, 

in feet above 

mean sea level
In the Casa Grande-Florence area, about 50,000 acres of 

Indian lands and 50,000 acres of privately owned lands are included in the San Carlos project, which was authorized by Congress in 1924. By 1930, water was available to the project from 

the San Carlos Reservoir, but the water supply never has been 

sufficient to irrigate the entire acreage. Supplemental water for 

project lands is obtained from wells that discharge into canals 

and laterals.

Little ground water was pumped in the lower Santa Cruz 

basin before 1924. The phenomenal expansion of ground-water 

pumping for irrigation after World War II has caused cumulative decline of water levels in the Santa Cruz basin (fig. 6). The 

current decline is rapid and in some places has extended to the 

flanking mountain slopes. The central valley floor is sinking 

because the dewatered land tends to shrink. Long earth cracks 

have developed near the mountain flanks. At the margins of 

the basins, the decline is less than that in areas where pumping 

is concentrated. If the water table continues to decline in the

Grand Canyon National Park, from Bright Angel Trail.
The Grand Canyon.

central part of the valley, pumping for irrigation may become 

too expensive to continue. Even before the underground storage 

supply is exhausted, the high lift necessary may increase the cost 

to uneconomical levels.

The Colorado River

Almost the entire State of Arizona is in the basin of the 

mighty Colorado River. Yet so important is water in this part 

of our country that the use of Colorado River water has been a 

subject of controversy for more than 30 years.

In 1921 Congress authorized construction of Boulder (now 

Hoover) Dam, an initial effort to prevent floods, store water, develop power, and control flow on the Colorado River. The 

authorization aroused much controversy among the seven basin 

States Arizona, California, Colorado, Nevada, New Mexico,

23
Utah, and Wyoming. Congress was reluctant to pass the authorizing bill unless at least six of the seven States, including California, agreed on how the water was to be divided. In 1922 

representatives of the seven States drew up a compact which 

divided the water between an upper basin and a lower basin, 

with the point of division at Lees Ferry in northeastern Arizona. 

The compact allots an average of 7.5 million acre-feet of water 

per year to the upper basin and a like amount to the lower basin, 

which includes parts of Colorado, California, and Nevada. In 

addition, the lower basin is permitted to increase its annual beneficial consumptive use of Colorado River water by 1 million 

acre-feet of water.

In 1923 all the States ratified the compact except Arizona. 

Congress then passed the Boulder Canyon Project Act (1928) 

and the Secretary of the Interior was authorized to let contracts 

for water and power with States which had ratified the compact. 

Under the terms of the act, a limitation of 4.4 million acre-feet 

was set for California, while 2.8 million acre-feet was recommended for Arizona and 300,000 acre-feet for Nevada. Further division was to be made of any surplus. Arizona, California, 

and Nevada could not reach the agreement suggested by the 

Congress in the Boulder Canyon Act. In 1952, after several 

previous legal moves, Arizona filed suit relative to the division 

of Colorado River water. Subsequently, the Supreme Court 

rendered an opinion and issued a decree dated March 9, 1964, 

implementing the opinion. It will probably take several years 

for water development and use in the lower basin to adjust to the 

provisions of the Supreme Court decree.

This brief history of water development reveals that almost 

everywhere in Arizona surface-water supplies are modest or else 

oversubscribed. The ground-water resource has been used to 

compensate for the lack of surface water, but intensive groundwater development has resulted in steadily declining water levels in 

the irrigated areas of Arizona.

The story of water in Arizona to date is one of maximum development with minimum planning or regulation. This trend 

has produced agricultural products in abundance, as well as 

all the accompanying benefits of a high standard of living. But 

the question remains: Can increasing development of ground

24
and surface water continue in its present pattern in the face of 

the ever rising costs for pumping (because of constantly increasing depth to ground water), and without eventually depleting 

the ground-water reserve?

Grand Canyon National Park, from Kaibab Trail.

25
THE 

PRESENT

Water resources

The most outstanding characteristic of Arizona is diversity 

of scenery, climate, weather, and streamflow, as well as plant and 

animal life. The climate is related to the mountains and plateaus 

and to the prevailing westerly winds. The cold desert country 

to the north offers scenic beauty to the tourist and provides limited 

pasturage for grazing sheep and cattle. In the hot deserts of 

the south, agriculture and industry flourish where water is diverted from streams or pumped from underground storage.

Annual precipitation in Arizona ranges from about 3 inches 

in the desert to 30 inches in the mountains. Streamflows are 

very erratic, fluctuating widely from year to year. Because of 

this variability, storage of surplus water is vital to water management in Arizona.

A glance at the map (see fig. 1) will show that Arizona is 

naturally divided into three major regions: the Desert Lowlands 

in the south, the Central Highlands running east-west across the 

State, and the Plateau Uplands in the northern half of the State. 

Water conditions and water problems are different in each of

26
these three regions because of differing geographic and geologic 

conditions.

The rugged, mountainous central region has been carved by 

streams into spectacular landforms (fig. 7). The Mogollon Rim, 

a distinctive feature of grandeur and prominence, extends more 

than 200 miles through the central part of the State and ranges 

in height from several hundred feet to more than 2,000. Its brow 

is the divide between the drainage systems of the Little Colorado 

and Gila Rivers. Springs along the base of this south-facing 

escarpment feed water into the Gila, Salt, and Verde Rivers.

Principal Gila River tributaries that rise in the Central Highlands include the Verde River, which flows southeastward through 

the central part of the State, and the Salt River, which drains the 

eastern area lying south of the Mogollon Rim.

Precipitation in the mountains ranges from 10 to 35 inches 

annually (fig. 8). Westerly winds cool as they rise over the steep 

mountain slopes, form clouds, and create a virtual squall line 

along the rim's crest from late morning until late evening during 

the summer. Similar conditions may prevail during the winter 

and cause heavy snowfall. Melt water from snow provides a large 

part of runoff late in the spring.

Water from the Central Highlands flows southward in the Salt 

and Verde Rivers and northwestward in the Little Colorado 

River. The Salt River and Tonto Creek join in the highlands 

(fig. 9) and discharge to the lowlands through the narrow Salt 

River gorge east of Phoenix. The Salt and the Verde Rivers 

carry most of the surface-water yield from the region, and the 

gorge funnels most of this water to the Phoenix area.

Surface runoff varies widely from place to place in the mountains, owing to differences in precipitation, temperature, and 

terrain. South and immediately west of Mount Baldy, precipitation exceeds 25 inches a year (fig. 8), and the average annual 

runoff is about 4 inches. ("Four inches of runoff" means a 

volume of water equivalent to a layer 4 inches deep over the 

entire watershed.) West of Baldy, along the upper reaches of 

Forestdale and Carrizo Creeks, annual rainfall exceeds 20 inches, 

but runoff is less than 1 inch. Farther west, in upper Tonto Creek 

basin, runoff is more than 2 inches. The average for the Salt 

River drainage system above Roosevelt Lake is 2.8 inches, or 

somewhat more than 600,000 acre-feet a year.

681-100 O-66 4 27
Bill Williams Mt San Frai

Valley Fill 

Wafer bearing

Volcanic Rocks and

Associated Sediments

Wafer bearing in some places

Granite Schist

Basement Rocks

Non-water-bearing, except in fractures

S

Undivided Paleozoic and 

Mesozoic Rocks 

Non-water-beoring

Coconino Sandstone 

Wafer bearing

Undivided Paleozoic Rocks 

Non-water-bearing, except in fractures

Fault, dashed where inferred 

Water bearing in many places

Perennial Stream

Intermittent Stream

Diversion Canal 

For distribution to irrigated lands

Figure 7. The Central Highlands of Arizona.

28

CITY OR TOWN 

© Casa Grande 

© Flagstaff 

© Globe 

© Mesa 

© Phoenix 

© Prescott

S

Safford 

Tempe 

Tucson
Mt Baldy

Black River

29
The streamflow characteristics of the Verde River basin, in 

the western part of the province, resemble those of the Salt River. 

Several upstream tributaries, such as Oak and Granite Creeks, 

have an average annual runoff of about 4 inches (fig. 9). At 

the mouth of the Verde, the annual average is only 1.4 inches, 

or 500,000 acre-feet. Because Agua Fria and Hassayampa Rivers drain areas at lower altitude, their runoff is considerably less 

around 0.5 inch.

EXPLANATION 

LESS THAN 10 INCHES 

10 TO 15 INCHES 

15 TO 20 INCHES 

20 TO 25 INCHES 

25 TO 40 INCHES

25 25 50 MILES

Figure 8. Average annual precipitation.

30
Flagstaff

/ Winsk>wLf--A

EXPLANATION A 75,000 

125,000 

250,000 

500,000 

750,000 

1,000,000 

1,500,000 30,000,000 

Average yearly discharge Average yearly discharge 

in tributary drainage, in of Colorado River in 

acre-feet acre-feet

i

5,000,000 Width of arrow indicates amount of woter 

10 000 000 diverted through canals to irrigated lands

20,000,000 --- !! ! 

Perennial

Intermittent 

Figure 9. Annual discharge of Arizona streams.

31

681-100 O-66 5
The San Francisco and San Carlos Rivers and Eagle Creek are 

the main drainageways in the southern part of the Central Highlands, from which streams flow southward to join the Gila above 

Coolidge Dam. Their average annual runoff is less than 0.6 inch.

Most floods in the central highlands are caused by storms moving eastward from the Pacific coast, most frequently in winter 

or early spring. The largest flood of record on the Salt River, 

in February 1891, had a peak flow of 300,000 cfs (cubic feet 

per second) just below the mouth of the Verde. The peak discharge of this flood is about the same as that of the largest flood 

known to have occurred on the main stem of the Colorado River. 

This widespread storm also caused the maximum flood of record 

(46,000 cfs) at Planet, on the Bill Williams River in the western 

part of the State.

The second greatest flood on record occurred in November 

1905, when peak flow of the Verde River near its mouth was 

96,000 cfs. Floods were widespread also in January 1916, and 

on several streams these rank variously as second or third highest 

in the last 70 years. Other noteworthy floods occurred in February 1937, March 1958, March 1941, and January 1952.

Storms originating in the Gulf of Mexico occasionally cause 

unusual floods. A peak flow of 27,000 cfs on August 1951 is the 

maximum for the Hassayampa River since 1938. The same 

storm caused the highest recorded summer peak on Tonto Creek, 

31,000 cfs, the fourth highest of record since 1941. Another unusual summer storm occurred in,August 1954, sending a maximum flow of 43,000 cfs down Queen Creek.

In general, flood stages from winter storms are persistent, and 

stream discharge may remain high for several days. Floods from 

summer storms rise rapidly to a sharp peak, followed by rapid 

decline.

Sixty percent of the annual runoff in the Salt River occurs between January and April, compared with 15 percent between 

July and September. Runoff in the Verde is 65 and 15 percent 

during the same periods. Minimum flows usually occur just before the summer rain^, in June or early July. June runoff in the 

Salt and Verde Rivers averages only 3 percent and 1.5 percent of 

the annual total.

An outstanding characteristic of the Phoenix area is the extreme variability of the annual runoff (fig. 10) in the Salt River.

32
Runoff ranged from a low of 290,000 acre-feet in 1900 to a 

high of 5,200,000 in 1905. Base flow before intensive development is reflected in the annual lows of June and October. Base 

flow as used here refers to ground water that is discharged into 

streams. The slow movement of this water sustains the discharge and enables streams to continue flowing even when there 

has been no rain for a long time.

Three main rock types occur in the mountains: sedimentary, 

igneous, and metamorphic. Each of these has a different physical makeup, and each differs from the others in its ability to 

store and transmit water and in the chemical quality of its 

water. Igneous rocks are formed from the molten rock, or 

magma, which pushes through crevices in the earth's crust and 

solidifies. Sedimentary rocks are made from the sediments laid 

down by aniient nvers and winds. Metamorphic rocks may 

have begun as igneous or sedimentary rocks, but heat, time, pressure, and sometimes water have changed them into another kind 

of rock.

Igneous rocks in the Central Highlands are mostly granite. 

Among the metamorphic rocks, schist and gneiss are common. 

These rock varieties are nearly impervious to water and have 

little capacity for water storage except where they are intensively 

fractured.

The sedimentary rocks that form the Mogollon Rim consist of 

firmly consolidated sandstone, siltstone, claystone, and limestone. 

These rocks can store large quantities of water. But because 

they have low permeability, they are slow to absorb water or to 

yield it up once it is absorbed.

A large part of the rim is formed by the Coconino Sandstone, 

a major and widespread aquifer beneath the plateau. In many 

places, it is several thousand feet below the land surface, and 

in some places the water may contain too much chloride to be 

of use.

Many springs near the base of the rim discharge from the 

Coconino Sandstone or the underlying Supai Formation. Several springs occur along faults. The discharge from about 150 

of these springs, totaling some 180 cfs, sustains the perennial flow 

of many small streams to the south.

Flagstaff lies near the base of the volcanic San Francisco Mountain. The city obtains part of its water supply from wells in

33
the Coconino Sandstone in areas where faults and other fractures provide avenues for replenishment from precipitation. Permeable volcanic rocks, which form a large part of the land 

surface around Flagstaff, locally supply much water. Water 

from the surface moves freely through the volcanic rocks and 

recharges underlying beds.

A few valleys in the mountains contain alluvium, which is 

silt, sand, gravel, or similar material deposited by running water. 

Alluvial deposits are capable of storing ground water. Though 

these valleys extend for many miles, the alluvial deposits are 

shallow, and they do not contain as much water in storage as do 

basins to the south.

GROUND WATER IN SALT RIVER VALLEY

180

2500

TOTAL ANNUAL PUMPAGE IN SALT RIVER VALLEY

£ 2000

Q uj uj rae i I

1890 1895 19001905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 1960 1965 

. CALENDER YEARS

Figure 10. History of ground and surface water in Salt River Valley.

34
4500

4000

3500

3000

2500

2000

1500

1000

500 

2000

1500

1000

500

COMBINED STORAGE IN SALT AND VERDE RIVER SYSTEM OF RESERVOIRS

1500

1000

500

YEARLY DIVERSIONS FROM SALT AND VERDE RIVERS AT GRANITE REEF DAM

1890 1895 1900 1905 1910 1915 1920 1925 1930 1935 1940 1945 1950 1955 19601962

CALENDER YEARS A

35
Alluvial sediments in Safford Valley contain ground water, but 

the potential yield is small because most of the sediments are 

fine grained. Only the shallow unconsolidated material, about 

80 feet thick along the Gila River, will yield water readily. 

Although hydrologic conditions in the upper part of the Verde 

River valley generally resemble those in the Safford Valley, there 

are many local differences that affect the quality and quantity of 

ground water obtained from the valley sediments.

Plantlife varies widely with climate and altitude. Nowhere 

in the State are variations more pronounced than in the Central 

Highlands. In many places temperature, precipitation, soil types, 

and other environmental factors favor luxuriant growth.

As you leave the Desert Lowlands behind and climb upward, 

the first noticeable change in vegetation is the occurrence of 

chaparral along the base of the mountains, where moisture is 

somewhat more plentiful. Chaparral includes a wide variety 

of shrubs such as live oak, manzanita, desert ceanothus, sumac, 

buckthorn, and silktassel. Grasses are more abundant in the 

chaparral zone than at lower altitudes, but the main grassland 

zone is higher.

Vegetation in the highlands.

36
Many parts of the upper grassland zone have been invaded 

by juniper. Where this tree is well established and its density 

adjusted to the available water supply, little moisture is left for 

grass. The ground beneath the trees is barren. Ponderosa pine 

predominates at altitudes between 6,000 and 8,000 feet. Above 

8,000 feet are spruce, fir, and aspen. Each zone merges gradually with its neighbor, and there is no distinct line of demarcation between the several zones. Pine may occur with spruce and 

fir in the upper part of the ponderosa zone and with juniper in 

the lower. Each tree zone has an understory of shrubs and 

grasses.

When rain or snow falls in forests some is intercepted by vegetation. A shower may wet an entire tree thoroughly; yet no water 

reaches the ground under the tree. After the shower the water 

soon evaporates. Vegetation probably intercepts considerably 

more snow than rain. Snow may lodge thickly on the needles 

and branches of conifers, and much of it evaporates unless blown 

off by the wind.

Although we have no good measure of how much water is 

intercepted by forest vegetation, we do know that the amount

37
is substantial. More information about interception of precipitation by vegetation is needed.

Geology, topography, and climate influence the quality of surface and ground water. The quality of water at a point in a 

stream depends to some extent on the upstream conditions, and 

the character of the water will change from place to place. The 

chemical and physical changes in surface waters can be easily 

detected over short time intervals, hours or days. Whereas, 

changes in the quality of ground water, owing to the complex relations of the materials through which it flows, occur over much 

longer periods of time.

The numerous small mountain creeks flow swiftly; they carry 

cool, fresh water and are usually free of sediment because the 

water flows over granite, schist, and volcanic rocks, which do 

not erode easily. During periods of storm runoff, however, the 

streams contain large amounts of sediment. In the upper reaches 

of the streams, the water contains little dissolved minerals.

Springs in the Salt River below Cibecue Creek contribute 

small amounts of highly mineralized water to the Salt River and 

to a few of its tributaries above Roosevelt Lake. Nevertheless, the 

quality of water released at Stewart Mountain Dam is good because fresh floodwaters are mixed with the saline spring water 

in the Salt River reservoirs.

Below Stewart Mountain Dam the average concentration of 

dissolved salts was less than 700 ppm (parts per million) between 

1951 and 1957. (Parts per million is one way of expressing the 

weight of dissolved matter in a solution. One part per million 

equals 8.34 pounds of dissolved solids in a million gallons of 

water.) In the course of a year, more than 400,000 tons of 

salts are carried by the Salt River below Stewart Mountain 

Dam. The Gila River at Kelvin carries about 142,000 tons 

per year, and the average load of the Verde below Bartlett Dam 

is about 110,000 tons (fig. 11).

The plateau in the northern part of Arizona represents almost 

40 percent of the total area of the State a vast expanse of magnificent scenery. The climate is cool and the country arid. This 

is the land of the Navajo, the domain of the Little Colorado 

River. The gently sloping surfaces, covered with a thin mantle 

of soil and sparse grass, provide grazing land for sheep, a major

38
SCALE IN TONS

500,000

375,000

250,000

125,000

© Colorado River

at Lees Ferry, Ariz.

@ Colorado River near 

Grand Canyon, Ariz.

(3) Colorado River below

Hoover Dam, Nev.-Ariz.

@ Colorado River 

at Yuma, Ariz.

© Gila River below

Gillespie Dam, Ariz.

© Verde River below 

Bartlett Dam, Ariz.

Q) Salt River at

Stewart Mtn Dam, Ariz.

(§) Gila River at Kelvin, Ariz.

Little Colorado River at 

Woodruff, Ariz.

Figure 11. Average loads oF dissolved salts in Arizona streams.

factor in Navajo economy. Another factor is the scanty water 

supply.

The ribbon of high precipitation that extends along the brow 

of the Mogollon Rim in the mountains bends northward past 

San Francisco Mountain to the Kaibab Plateau, where it supports 

forests of juniper and pine. Spruce, aspen, and fir grow at higher 

altitudes.

The Colorado River flows across the northwest part of the 

State, where it has sculptured the inspiring spectacle of the Grand 

Canyon. Persons from all over the world have seen the ancient 

colored rocks and marveled at the depth of the tremendous 

chasm. To the east the Little Colorado, an important upland 

tributary, flows along a shallow valley to Grand Falls, where it 

tumbles into a deep gorge. Throughout the plateau, erosion 

has carved the rocks into a great variety of landforms such as 

Monument Valley and the Painted Desert. The natural coloring in this part of the State is exceptionally vivid.

681-100 O-66 6

39
1

Junction of the Colorado and Little Colorado Rivers and south rim of Grand 

Canyon at Grand Canyon Village.

Almost all perennial streams which flow across the plateau 

originate in the mountains, where precipitation is high along 

the Mogollon Rim. Melting of winter snows tends to prolong 

the flow in some streams, but during the summer most of the 

streams flow only after rain.

The canyons of the Colorado and Little Colorado cut through 

several thick aquifers which discharge water as springs. Surface 

runoff and discharge from springs constitute the perennial water 

yield of the plateau. Some of the water is good in quality, some 

is very salty. Little of it is captured for beneficial use.

Because evaporation is high, streams here yield very little water 

in proportion to the sizes of their drainage areas. A typical example is the Little Colorado River, which drains a vast area of 

over 26,000 square miles, yet is intermittent through most of its 

course. (See fig. 9.)

Streams that flow northward lose a small part of their water 

by seepage into the ground. The rocks near the surface transmit 

'water very slowly; so downward movement is slow, and much of 

the water is evaporated or transpired from the soil zone near the 

surface. The ground water also moves very slowly a few inches 

a day at most. Much of the water remains in the ground for 

many centuries before it is discharged. Generally, wells on the 

plateau yield little water; however, there are marked exceptions 

where local geologic conditions favor high productivity. Most 

of the ground-water supply of the plateau is undeveloped, and 

full development may never occur because of the difficulty of 

extracting the water from the ground.

The principal area of natural discharge for ground water in 

the uplands is near the junction of the Colorado and Little Colorado Rivers. There, Blue Springs discharge about 160,000 

acre-feet of water annually into the Little Colorado.

40
Geologic conditions, as well as sparse rainfall, tend to keep 

the plateau arid, with only scanty vegetation. The Chinle Formation of Triassic age forms a large part of the ground surface. 

This formation consists of fine-grained siltstone, claystone, and 

some sandstone and limestone. In the Hopi Reservation, Cretaceous shale and sandstone are the main surface rocks. Here, 

the Little Colorado River obtains its large sediment load from 

these easily eroded formations.

Fractured limestone, which forms the surface rocks between 

Winslow and Flagstaff, permits water to percolate from the land 

surface downward into the underlying Coconino Sandstone (fig. 

12). These subsurface units, the Coconino Sandstone and the

Carrizo Mts

Chusko Mts

City or Town 

(j) Cameron 

@ Flagstaff

Halbraak 

3) St. Johns

Snowflake 

@ Winslow

Granite Schist

Basement Rocks

Non-water-bearing, except in fractures

esaverde Group 

X

w bearing in places

vided Jurassic and 

retaceous Rocks 

f/y non-wafer-bearing

Undivided Triassic Rocks 

Water bearing

Coconino Sandstone 

Wafer bearing

Undivided Paleozoic Rocks 

Non-wafer-bearing

Undivided Precambrian Rocks 

Wafer bearing in places

Fault, dashed where inferred 

Wafer bearing in many places

Perennial Stream 

~^...^

Intermittent Stream

Figure 12. Geology of the Plateau Uplands.

41
THOUSANDS OF ACRE-WET PER Y 

6 78 9 10 11 12 13

upper part of the Supai Formation, are the main aquifers and 

yield water to wells and springs throughout the region. Another 

feature of the region is "aquicludes," rock units or layers of finegrained materials through which little or no water can move. 

Such an impervious layer overlying an aquifer leads to the development of artesian pressure in the water-bearing formation.

The aquifers in this region are not very productive, but the 

people living on the plateau depend upon them. The Navajo 

Sandstone supplies water in the western part of the reservation, 

but it thins out eastward and is absent in the eastern part. Erosional features also are important. For example, the Cretaceous 

sandstones which yield water in Black Mesa are absent elsewhere. 

Near the Colorado River, where these rocks have been eroded, 

little ground water is available.

Annual runoff from the plateau is generally less than 0.3 inch, 

except in streams originating just north of the Mogollon Rim and 

those rising just south of the Kaibab Plateau. The principal 

streams north of the Mogollon Rim are Clear Creek, Chevelon 

Fork, Show Low Creek, and the West Fork of the Little Colorado 

River northeast of Mount Baldy. Runoff from headwaters of

42
60 75 90 105 120 135 150165

Figure 13. Discharge of 

springs in the Grand 

Canyon area.

these streams ranges from 2 to 4 inches, but the average is less 

than this from areas near the Little Colorado.

The average annual runoff in Clear Creek at the mouth is 1.6 

inches and in Chevelon Fork only 0.6 inch. Runoff from the 

headwaters of Silver Creek is about 3 inches, but consumptive use 

on more than 6,000 acres of land irrigated from it reduces the 

average annual runoff at the mouth to only 0.3 inch. Similarly, 

the flow of the upper Little Colorado passes through many small 

reservoirs, and the water is used to irrigate about 6,700 acres 

upstream from Lyman Reservoir. Measured just above the reservoir, the average annual runoff is only 0.3 inch. The large 

expanse of arid lands on the north side of the Little Colorado, 

mostly in Navajo and Hopi Indian Reservations, has an average 

annual runoff of less than 0.25 inch.

Many tributaries enter the Colorado River between Lees Ferry 

(Lees Ferry is approximately the dividing point between the 

upper and lower basin States), and the head of Lake Mead. Most 

of the tributaries flow only during periods of heavy rainfall, but 

several are fed by springs and are perennial (fig. 13). The total 

contribution of these spnngs to the Colorado is not known exactly

43
but must be about 300,000 acre-feet per year. The largest contributor is Blue Springs, which emerge about 10 miles above the 

mouth of the Little Colorado and yield some 160,000 acre-feet 

of water annually, and about 500,000 tons of dissolved salts. 

The second largest group emerges in Havasu Creek just above 

Hualapai, a tributary draining from the south side of the Colorado 

River near the western part of Grand Canyon National Park. 

The second group contributes about 45,000 acre-feet per year to 

the Colorado.

Bright Angel Creek and Tapeats Creek (Thunder River) 

originate below the Kaibab Plateau on the north side of the Colorado. On the basis of surface drainage area their apparent average annual runoff at the mouth is 5 to 10 inches. This indicates 

that the streams are fed from springs whose water probably comes 

from precipitation in the high plateau area beyond the surface 

drainage boundary. Bright Angel Creek contributes an average 

of 26,000 acre-feet per year to the Colorado River. The estimated annual flow in Tapeats Creek is about 50,000 acre-feet.

We noted earlier that the main aquifers on the plateau are finegrained sandstones with alternating layers of siltstone and claystone. Even the beds which yield little water play an important 

role in ground-water occurrence. Beginning with the formations at greatest depth (fig. 14), we find the following more important aquifers:

The Supai Formation contains alternating beds of sandstone, 

siltstone, and mudstone nearly impervious to water.

The Coconino Sandstone is of Permian age and underlies nearly 

all the area. It averages about 600 feet in thickness, but thins 

eastward to about 200 feet. The formation consists of fine wellsorted sand which was deposited by ancient winds. (By well 

sorted we mean that the grains are all about the same size. Wellsorted formations hold more water than poorly sorted ones.) In 

places, the formation is fairly impervious.

The Navajo Sandstone of Jurassic age is the aquifer next in 

importance to the Coconino. It is fine grained and well sorted 

and contains only a small amount of cemented material. It 

consists of ancient dune deposits, and it is the principal waterbearing formation in the western part of the Navajo Reservation. Wedge shaped, the formation is about 1,500 feet thick

44
30

30'

30'

00

00

DO

00'

Volconic rock '////A. Water bearing in places 

Volcanic rock- v

MESAVERDE 

_ GROUP

Water bearing

Black shaly 

siltstone and

DAKOTA SANDSTONE

MORRISON 

FORMATION Lower Red siltstone and

COW SPRINGS SANDSTONE

ENTRADA SANDSTONE

Red and white shaly siltstone and massive mudston CARMEL FORMATION

NAVAJO SANDSTONE

KAYENTA FORMATION

WINGATE 

- SANDSTONE

Lower Reddish-brown shaly siltstone

CHINLE FORMATION Varicolored shaly siltstone, mudstone, and claystone

SHINARUMP CONGLOMERATE

MOENKOPI FORMATION Red siltstone

KAIBAB LIMESTONE

COCONINO SANDSTONE

SUPAI FORMATION Red siltstone, mudstone, fine-grained sandstone

Figure 14. Rock formations in Navajo country.

45
near Lees Ferry and thins southeastward and disappears near 

Ganado.

The Mesaverde Group is a series of sandstone, shale, and silt 

units of Cretaceous age. These yield a small amount of water 

in the Black Mesa area.

Sedimentary and volcanic (igneous) rocks in the SpringervilleSt. Johns area are water bearing, but their storage capacities are 

small. The volcanic materials are porous and act as collectors, 

enabling water to percolate into the underlying sediments. 

Ground water is obtained also from shallow alluvium along 

major drainage systems such as that of the Little Colorado and 

its tributaries in the Navajo and Hopi country (fig. 12). Storage 

capacity of these deposits also is limited. The fine-grained character of the alluvial material is not favorable for sustained large yield 

through wells. Well yields range from a few gallons per minute 

to 200 gpm.

The main aquifers in the plateau uplands contain large amounts 

of water, but the rocks are low in permeability and do not readily 

yield large quantities of water. Wells seldom yield as much as 

300 gpm.

Where sandstone aquifers have been faulted and jointed, additional storage space and greater permeability are provided. At 

such places these aquifers will yield considerably more water. 

Such conditions prevail near Flagstaff, St. Johns, and Snowflake. 

Similarly, a few miles east of the confluence of the Little Colorado 

and the Colorado, faulting probably accounts for a large spring 

flow from the Coconino Sandstone in the Black Mesa basin.

Although ground water occurs widely in the uplands, its chemical quality is varied, and much of it is unfit for use (fig. 15). 

Some rocks that contain good water yield only small amounts. 

The variation in quality is accounted for by differences in the 

mineral composition of the rocks through which the water moves. 

At places, water in the Coconino Sandstone is too highly mineralized, and in much of the region the water is too far below the 

surface for development under present economic conditions. An 

1,800-foot well penetrating this aquifer northwest of Holbrook 

yields water containing more than 10,000 ppm of chloride. Although excellent water is available from the Coconino in its recharge areas, there is little hope for developing large supplies of 

good quality in the central part of Black Mesa basin.

46
CONSTITUENTS, IN 

ARTS PER MILLION

600

400

200

0

CI,F,N03

|so4

|HC03

Na,K

I Ca.Mg

JIDAHOCHI FORMATION

MESAVERDE GROUP

MANGOS SHALE________ 

DAKOTA SANDSTONE 

MORRISON FORMATION 

COW SPRINGS SANDSTONE 

ENTRADA SANDSTONE 

CARMEL FORMATION_____ 

NAVAJO SANDSTONE

KAYENTA FORMATION 

WINGATE SANDSTONE

CHINLE FORMATION

SHINARUMP CONGLOMERATE 

MOENKOPI FORMATION 

KA BAB LIMESTONE______ 

COCONINO SANDSTONE

SUPAI FORMATION

Figure 15. Analyses of representative ground waters from important waterbearing rocks in the Plateau Uplands.

47
Streams on the plateau carry more sediment than those in any 

other part of the State, for the rocks that form much of the surface there are easily eroded. The amount of sediment added to 

the Colorado by its tributaries is tremendous. The Paria and 

the Little Colorado yield an average of 14 million tons each year. 

Sediment yield of streams in the uplands varies greatly, owing 

to runoff fluctuations. Half the annual load of suspended sediment in the Little Colorado and Paria sometimes is moved in a 

day or two, and more than nine-tenths of the annual load may 

be carried in a month. Measured near Grand Canyon, the average annual load of sediment in the Colorado River is more than 

150 million tons (fig. 16).

Stream water becomes salty where it comes in contact with 

rocks composed of easily dissolved minerals such as common salt 

and gypsum. Dissolved salts in waters of the larger upland rivers 

usually amount to less than 700 ppm. On the other hand, water 

in some of the smaller intermittent streams contains 1,000 to 2,000 

ppm. But flows of the more highly mineralized waters are small 

compared to those of the Colorado; so the mineral waters are 

diluted in the purer waters of the Colorado.

The Desert Lowlands contain more than 80 percent of the 

State's population. Many persons prefer living and working where 

the climate is hot and dry the year round. For agriculture, the 

hot climate provides one of the longest growing seasons in the 

United States, and the rapidly increasing population provides an 

adequate labor supply. Thus, the Desert Lowlands furnish favorable conditions and an unusually attractive setting for healthful 

living, prosperous agriculture, industry, and mining. Here is a 

typical boom society on the receiving end of the westward 

movement.

There are fewer visible evidences of water shortage here than 

in many areas of the country considered to be far richer in water. 

About 7 million acre-feet of water is diverted or pumped yearly 

for irrigating about a million acres in this region. Industry and 

municipalities use about 300,000 acre-feet and another half a 

million acre-feet could be put to good use immediately. Almost 

2.25 million is obtained from surface water 1.25 million from 

the Salt, Verde, and Gila Rivers impoundments and nearly 1 

million diverted from the Colorado north of Yuma.

48
Virgin River at 

liHtefield

Porto River at 

lees Ferry

Colorado River at 

Lees Ferry

'Yorm '?

j

*^^

-* *. 

t ZP.

\.

X. i

Tucson'fc 1 --

/

-^

0 25

i i 1 1 1

Y s-

' N N

\. ^ 1

\ f I

, . v. Douglas | 

JL--i. -Nt50 MILES i

SCAIE, IN TONS 

m ACRE-FOOT

Figure 16. Average loads of suspended sediment in streams on the Plateau

Uplands.

Nearly 5 million acre-feet of the water now used annually 

comes from ground-water reservoirs. The areas of ground-water 

exploitation are in different stages of development. Ground-water 

supplies in some limited areas are practically unused, but are 

suitable for tapping at any time. Others are highly developed, 

or overdeveloped.

49
Consider surface-water supplies in the Salt, Gila, and Santa 

Cruz Rivers (fig. 9). Under natural conditions, the upper 

reaches of these streams lost water by percolation into the ground, 

thus feeding the ground-water system along the southern edge 

of the highlands. In turn, the ground-water system fed the downstream reaches of the stream where the water table was higher 

than the stream elevation. The natural recharge of ground water 

has been curtailed by upstream water use; so ground-water levels 

in the region would decline even if no ground water were pumped. 

However, ground water is being pumped; the decline of water 

levels is accelerating; and continued lowering is expected. Owing 

to curtailment of upstream runoff and the consequent decrease 

in ground-water discharge into the streams, the downstream 

reaches have long since ceased to carry water.

In the Desert Lowlands, precipitation is highest, of course, on 

the high mountain ranges. Near the top of the Catalinas, precipitation averages more than 30 inches annually, and the average 

yearly runoff is close to 5 inches. At the other extreme, precipitation is less than 5 inches and runoff is almost nil in the southwestern part of the State. Annual runoff from the driest 15,000 

square miles in the lowlands area averages less than 0.1 inch. 

The headwater areas of the San Pedro, Santa Cruz, and other 

large tributaries of the Gila River yield about 0.5 inch of runoff 

per year, but in downstream areas yields decrease to an average 

of 0.25 inch at Winkelman and Tucson. Runoff averages about 

0.15 at Whitewater Draw, 0.1 inch along San Simon Creek, and 

0.25 inch along the Bill Williams River at Alamo.

There are no large storage reservoirs for surface water in the 

Desert Lowlands. Several detention dams in San Simon basin 

were installed to reduce headward cutting of stream channels 

and to trap sediment that otherwise would be carried to the Gila. 

These structures have no operating gates, and they store water 

only for short periods. The capacity of Picacho Reservoir on 

the San Carlos project is about 18,000 acre-feet. It stores floodwater from the Florence-Casa Grande Canal. Many small stock 

ponds are scattered through the region, but most of these have 

surface areas of less than 2 acres. A great deal of water evaporates 

from these ponds; however, their effect on total water yield has 

not yet been evaluated.

50
Streamflow in the Desert Lowlands occurs mostly as flash runoff following thundershowers. A few lowland streams rise at 

higher altitudes, where snowmelt furnishes part of the runoff.

High in some mountain areas precipitation is more than 25 

inches annually. Streams originating there generally have perennial headwaters, but where they emerge on the alluvial basins, 

much water is lost by evaporation and infiltration. In the downstream reaches the flow is intermittent. (See fig. 9.) In desert 

areas the flow dwindles to nothing.

Storms originating in the Gulf of Mexico reach the southeastern corner of Arizona first and often drop their moisture over 

the mountainous headwaters of San Simon Creek, Whitewater 

Draw, and the San Pedro and Santa Cruz Rivers. Except for 

Whitewater Draw, these streams flow northwestward and join 

the Gila River. Whitewater Draw flows southward to join the 

Yaqui River in Mexico. These streams derive about three-fourths 

of their total annual runoff from thunderstorms in July, August, 

and September.

As floodwaters move downstream, several factors operate to 

decrease the flood peak and decrease the volume of runoff. These 

factors are: infiltration, evaporation, channel storage (the amount 

of water in the stream channel at any time), channel retention 

(the water required to fill the voids in the porous materials of the 

stream channel), and bank storage (water that seeps into the 

stream banks during high stages and drains back into the stream 

at lowered stages). In Arizona the decrease in volume of runoff 

is tremendously important. For example, runoff of floodwaters 

in the Santa Cruz River in August 1954 showed a loss of more 

than 2,000 acre-feet between Nogales and Cortaro (see fig. 17), 

a distance of 82 miles. No water at all reached the mouth of the 

Santa Cruz west of Laveen.

Below Cortaro, agricultural developments along the Santa Cruz 

use surface water for irrigation. But because there are no storage 

reservoirs on the stream, only a small percentage of flood runoff 

can be used. Natural losses of water between Cortaro and Laveen 

are high. In 1954, for example, some 53,000 acre-feet passed 

Cortaro, but only 9,400 passed Laveen, 94 miles downstream.

Below Gillespie Dam the Gila River traverses the area of lowest precipitation in the State, and natural channel losses are

51
Catalina

Figure 17. Disposition of water during a single flood, Santa Cruz River, 

August 23-25, 1954.

high. For example, from July 19 to September 10, 1955, 102,000 

acre-feet flowed past Gillespie Dam, but only 11,000 acre-feet 

passed Dome, 146 miles downstream. Moreover, the flow at 

Dome probably included some waste water from the WelltonMohawk irrigation project. The highest runoff year of record 

at Gillespie Dam was 1941, when 1,036,000 acre-feet passed the 

dam, but only 590,000 passed Dome. Because precipitation and 

flood runoff are low and channel losses high, the lower reaches of 

the Gila are dry during long periods. During the decade between 

September 1941 and September 1951, there were only 3 days 

when any surface flow passed the Dome gaging station.

Before 1880 many streams in the arid Southwest were depositing sediment along their lowland courses. In the decades that

52
followed they began to erode and to entrench their channels 

through those sediments. The most extensive trenching came in 

the late eighties, but the process is continuing in many areas.

Cutting of the Santa Cruz channel between Calabasas and 

Tucson was first noted in 1909. According to local residents, 

the flood plain was once covered with sacaton grass, and the river 

channel was insignificant. During floods, water spread over most 

of the grassy flood plain, and tules grew in boggy places. Late in 

the 1880's, ditches and cattle trails were enlarged by floods, and 

the present channel began to develop. At Tucson it is now 100 

to 300 feet wide and 12 to 15 feet deep.

San Simon Creek also has an interesting history. In the 1880's, 

when settlers from Utah reached the area, the present steep-walled 

channel did not exist. Trenching reportedly started in 1883 when 

the settlers excavated a channel 20 feet wide and 4 feet deep at 

Solomon to confine floodwaters. Since then the channel has been 

scoured 20 to 30 feet deep and has extended itself upstream about 

60 miles.

No single cause is responsible for the start of this erosion in this 

channel or others. Whether the principal cause was climatic 

change, overgrazing, exceptional floods (as in 1891), or some 

combination of causes, the fact remains that many stream channels in the lowlands changed radically. A complete analysis of 

the hydrology of this region would require a study of its erosional 

history as well as study of the subsurface conditions.

Figure 18 shows the geologic features of a typical area in the 

Desert Lowlands. Granite, gneiss, and schist are the principal 

rocks in the mountain blocks, but a few areas contain unmetamorphosed sedimentary rocks. Some of the mountain blocks are 

capped with volcanic rocks dating from recent time a most unusual feature. Some volcanic materials locally were erupted perhaps no more than 10,000 years ago. Most volcanic rocks are 

much older.

Geologists can reconstruct the history of erosion and deposition 

during past eons. The mountain blocks in the Desert Lowlands 

were pushed upward, and the basins were lowered by earth 

movements. These movements were accomplished by breaking 

(faulting) of the rocks along the edges of the mountains or by 

folding and warping. The basins were further excavated by

53
-4000

-Sea level Aquarius 

s.4000yfl;,Mts

Bradshaw Mts

4000 

Sea level 

4000

Undivided Valley Fill 

Water bearing

Undivided Tertiary and

Quaternary Volcanic Rocks

and Associated Sediments

Wafer bearing in placet

Undivided Paleozoic and

Mesozoic Sediments 

Essentially non-water-bearing

Granite Schist

Basement Rocks

Non-water-bearing, except in fractures

Undivided Cretaceous and

Tertiary Volcanic Rocks

and Associated Sediments

Water bearing in places

Fault, dashed where inferred

Diversion Canal 

For distribution to irrigated h

City ar Town

0 Aguila ® Phoen

(2) Casa Grande ® Salom

© Gila Bend © Tempi

0 Mohawk ® Welltc

© Mesa © Wicke

© Parker @ Yuma

Figure 18. Geology of the Desert Lowlands.

54
stream erosion that preceded the accumulation of alluvial sediments. Earth movement continued during the period of sedimentation. Volcanic eruptions also were common, and in places the 

volcanic rocks are interlayered with alluvial material; the interlayering indicates that some eruptions occurred while sedimentation was in progress. The prehistoric drainage pattern in the lowlands probably was quite different from that of today, and the 

ancient pattern has important bearings on the present occurrence of water.

Most alluvial valleys in Arizona passed through three principal 

stages of erosion and sedimentation. As is shown in figure 19, 

coarse sand and gravel were deposited on the floor of an ancient 

valley. The Arizona climate was more humid then than it is now, 

and large fresh-water lakes occupied the basins after the old gravel 

was deposited. Clay and silt beds accumulated in these lakes. 

These deposits rest on the old gravel in many places. Later the 

mountains were pushed upward and the lakes were drained. 

Subsequently, rapid erosion of the mountains again provided 

coarse materials which were deposited as valley alluvium. Erosion and sedimentation are continuing in the modern stage.

Permeability and porosity are among the most important physical characteristics of water-bearing materials. "Permeability5 is 

a measure of the ease or difficulty with which water passes 

through the materials. "Porosity" is a measure of the ability of 

the rock to store water. "Porosity of 25 percent" means that 25 

percent of a mass of earth or rock is pore space.

Fine-grained substances like clay, silt, and very fine grained 

sandstone may be highly porous, but the pores are generally very 

small; so these materials are poorly permeable or impermeable. 

On the other hand, gravel may contain less pore space, but the 

pores are large. Some gravel is so permeable that it will transmit 

millions of times as much water as dense clay whose porosity is 

relatively large.

Within the alluvial deposits the range in permeability is wide. 

Moreover, each kind of material contains particles of several 

sizes. Gravel, for example, may be composed largely of boulders, 

cobbles, and pebbles, but the deposit may also contain sand and 

clay. The fine sediments fill the spaces between coarse particles 

and reduce the porosity.

55 681-100 O-66 7
Stewart Mts

1000-

EXPLANATION

VALLEY FILL

Upper Sand and Gravel

Water bearing 1000'-

Clay and Silt (Lake Beds) 

Yields water of low rates

Lower Sand and Gravel 

Water bearing

BASEMENT ROCKS

Undivided 

Non-water-bearing, except in fractures

Perennial Stream 

Intermittent Stream

Figure 19. Alluvial basins in central Arizona.

Diversion Car

Water Level Pri 

Ground-water Pu

Water Level, Sprin

Alluvial materials in the desert basins of Arizona are unconsolidated or poorly consolidated, and they are far more porous 

than the aquifers on the plateau. Porosities of the alluvium range 

from 10 to 40 percent, and the average is about 25 percent.

The porosity of water-bearing material is a measure of the 

amount of water in the material, but it is not a measure of the

56
amount that can be removed. Rocks may have high porosities 

but yield little or no water if the pores are very small. Small 

pores hold water tenaciously, and the water moves through them 

very slowly. This is true of many lakebed deposits in alluvial 

basins. The porosity may be 50 percent or more, but the pores 

are so small that water moves through them extremely slowly. 

Time is thus an important factor in the yield of wells. Though 

the amount of water in an aquifer may be very large, one cannot 

withdraw water from a well faster than the water can move 

through the ground to the well.

The mantle of alluvial sediment, where it is present in the Central Highlands, averages only a few tens of feet in thickness, whereas in the Desert Lowlands its thickness ranges up to thousands of 

feet (fig. 19). Water that is discharged from the mountains into 

the basins seeps through the sandy floors of the basins and moves 

downward by gravity and becomes ground water. During past 

millennia, the ground water filled a large share of the pore space 

in sediments under the desert basins filled them to overflowing in 

some places. Today, however, the amount of water seeping underground from mountain-born streams, plus a small amount of 

rainfall that enters the basin sediments directly, is inadequate to 

replace the water that is discharged naturally and that is pumped 

by man.

Use of water

Arizona uses more than 7 million acre-feet of water annually, 

and more water will be needed to provide for growth, if it continues at the present rapid rate. Even now, for every 7 gallons 

of water withdrawn from the State's "water bank," only 2 is from 

surface water. The remaining 5 is obtained from reserves of 

water stored underground in the alluvial basins.

How is this 7 million acre-feet of water used?

The major beneficial use of water in Arizona is for irrigation, 

a process which by its very nature results in evaporation and transpiration of water. From 1936 to 1963, canals diverted an average 

of 1,250,000 acre-feet of water each year from streams other than 

the Colorado River. During 1948-63 annual gross diversions 

from the Colorado River ranged from 680,000 to 1,750,000 acrefeet. Surface return flows averaged more than 350,000 acre-feet;

57
Municipal Industrial Irrigational Municipal Industrial Irrigational Municipal Industrial Irrigational

Figure 20. Use of water.

so the net diversion did not exceed 1,400,000 acre-feet. The 1963 

net diversions of surface water for Arizona irrigation totaled about 

1,900,000 acre-feet per year (fig. 20).

Many small ponds have been built by farmers and ranchers to 

intercept and store surface water in ephemeral stream courses. 

Each pond captures most of the water reaching it. Livestock 

consumes very little of the trapped water, but the loss of water 

by evaporation is great.

The amount of water controlled by these ponds is unknown, but 

there are a large number of them, and they may be partly responsible for declining streamflow during the past 20 years.

58
After World War II the amount of ground water used for irrigation increased tremendously. In 1949 about 3.25 million acrefeet of ground water was used for agricultural purposes. This 

increased gradually to a peak of nearly 4.75 million acre-feet in 

1953, then dropped off slightly from 1953 to 1963. About 4.5 

million acre-feet was used for irrigation in 1963. The increase 

in irrigation with ground water is illustrated in figure 20. Figure 

21 shows the main agricultural areas in Arizona and how much

___ EXPLANATION

H 2,000,000 ACRE-FEET """

H 1,212,000 ACRE-FEET

H 160,000 TO 200,000 ACRE-FEET

JH 5 7,000 TO 87,000 ACRE-FEET

{ | 12,000 TO 37,000 ACRE-FEET 25 25 50 MILES

Figure 21. Ground-water pumpage for irrigation, 1963.

59
water was pumped in each during 1963. More than 75 percent of 

all the ground water used in 1963 was pumped in Maricopa and 

Final Counties.

Most irrigation pumps are within irrigated areas. Where 

transport ditches are lined, transmission loss of water is small. 

Ordinarily, irrigation water is applied somewhat in excess of the 

amount needed for optimum growth of crops, and some of the 

surplus returns by deep percolation to the subsurface reservoir. 

The amount of irrigation water returned to ground storage is an 

important item in the water budget, but data on the amount returned are not easy to obtain. Under some conditions the return 

may amount to one-quarter of the water applied for irrigation.

The chemical quality of irrigation waters apparently did not 

concern water users for many years. However, attention has recently been given to the relation of water quality and productivity of irrigated lands. Through the combined efforts of many 

individuals and State and Federal agencies, a fair knowledge of 

the factors necessary for successful irrigation has been accumulated. Nevertheless, much remains to be learned about the control of harmful salts in soils and irrigation water.

Lands with adequate water are valuable. Because water is 

scarce and therefore relatively costly, the agricultural trend has 

been toward such high-value crops as top-grade, long-staple cotton, citrus, melons, figs, dates, and lettuce. The long growing 

season permits double cropping with other products that also yield 

a cash return. High water costs encourage efficient use of irrigation water, and profitable crops are grown in some places with 

3 acre-feet or less per acre.

Large areas of fertile land in the lowlands still are desert, lacking only water to make them productive. Some of this land is 

being developed as additional wells are drilled, but there is more 

than enough land to use all the water that can be made available. Meantime, steady decline of the water table is a clear warning that there may be a ceiling on development. While new 

lands are placed in production, other land which had been cultivated is being retired. Retired land reverts quickly to desert.

The Indian names of some Arizona towns attest to the fact that 

the early settlers were very conscious of the importance of their 

water supply. Tucson, for example, meant the place of "dark

60
springs," Todilto Park stood for "sounding" or "splashing" water, 

and Todokozh Spring means "saline" spring or "sour" water.

But modern society and urban living impose demands on water 

supply undreamed of by the first settlers. Large population concentrations in arid regions create especially difficult water-supply 

and development problems. Municipal use has become a significant part of total water use in Arizona only in recent years. 

Municipalities used 40,000 acre-feet in 1949 and more than 

200,000 in 1957. The increased use is related directly to population growth. Larger urban areas like Phoenix and Tucson account for more than 80 percent of the total municipal use.

Most municipalities in Arizona use ground-water reservoirs, for 

their principal public supplies. Phoenix, which diverts 70,000 

acre-feet of water per year from the Salt and Verde Rivers, is an 

exception. This is the largest single development of surface water 

for a municipal supply in Arizona. Other municipal uses of surface water are small. Some water from the Black and San Francisco Rivers is diverted to supply the Morenci mines and the 

communities of Clifton and Morenci.

Ground-water development is usually less expensive, and surface supplies are not always available. Surface water usually requires filtration and purification, whereas ground water is less 

susceptible to contamination and commonly requires less treatment. For many places surface water would have to be transported over long distances.

Most Arizona cities drill wells for water supply. This is true 

of Tucson, Flagstaff, Prescott, Winslow, and Safford. Even 

Phoenix has turned to wells in the city to supplement the supply 

from the Verde River. Tucson once used Santa Cruz River

Irrigation at Yuma project and young citrus groves in the Gila project.
water, but the river ceased to flow long ago. Tucson's entire supply is now obtained from wells.

Practically all surface waters in Arizona streams have been appropriated for irrigation. As a result ground water has had to 

be developed for urban use. The settlement of water rights, 

whether for surface water or ground water, is a serious problem 

for each expanding community.

Arizona's largest and fastest growing urban area is Phoenix, the 

State capital. This city is proud of its streets, parks, homes, and 

business section. Green lawns, shade trees, and flowering plants 

flourish everywhere. Swimming pools dot the landscape. 

Phoenix is said to be as completely air conditioned as any community in the West. Nearly every home and place of business 

is equipped with an air conditioner. These comforts use much 

water. Situated in a desert environment, the city is virtually an 

oasis with metropolitan comforts. Within the canal system the 

land is green; beyond the canals is the desert.

Each year more and more winter visitors become residents of 

Phoenix. The population increased from 92,000 in 1946 to 

173,000 in 1958, nearly doubling in little more than a decade. 

Meanwhile, water use more than doubled. As of mid-1963 the 

population was 507,000.

The fast-growing city of Phoenix.

62
Phoenix is fortunately situated for municipal water development. The Salt River Canyon is a very convenient hydrologic 

funnel through which flows the State's principal perennial water 

supply (though the Colorado River flow is greater, only part of it 

can be used in Arizona). A part of the water for the city is obtained from the Salt and Verde Rivers just above and below their 

junction; this water is collected in horizontal galleries and vertical wells in alluvium near the river channel or pumped directly 

from the rivers. From these it is pumped to a large watertreatment plant just above Granite Reef Dam and thence by 

pipeline to Phoenix. Water from canals, and from wells within 

the city limits, supplements this supply.

In 1946 an average of about 18 mgd (million gallons per day) 

came from the Verde, and another 5 mgd was pumped from wells 

to obtain the daily average of 22.5 million gallons. By 1963 the 

average use increased to about 120 mgd. About 33 mgd came 

from the Verde and Salt Rivers. Another 31 mgd was taken 

.from the Water Users' canal system at Squaw Peak pumping 

plant; most of this water came from the Verde and Salt Rivers. 

The remainder was ground water. Pumpage varies greatly 

throughout the year. On January 3, 1963, for example, the city 

used 45 million gallons of ground water; while on July 25 of the 

same year, it required about 100 million.

The municipal supply system serves about 95 percent of greater 

Phoenix. The wells produce a little more than 1,500 gpm each, 

and the average pumping lift is about 250 feet.

Water from the Verde and Salt Rivers is good in quality. It 

contains only 300 to 400 ppm of dissolved solids. But ground 

water pumped near Phoenix contains 700 to 800 ppm. The 

ground water must be treated before large quantities can be put 

in the city water system. Therefore, the city prefers to draw 

on the Verde River for as much of the total supply as possible.

All water in the Verde River has been appropriated, and most 

of it goes into the irrigation system of the Salt River Valley Water 

Users. Yet Verde River water has always been an important 

factor in the economy of Phoenix, and two large dams have 

been built on the river to impound the supply and regulate 

streamflow. Phoenix lies in the middle of the Water Users' 

project, and urban growth has caused a reduction of land under

63
cultivation in the project. New city subdivisions are sprouting 

on formerly agricultural land. By paying the Salt River Valley 

Water Users' Association for these rights, Phoenix has obtained 

additional water from the Verde and Salt Rivers.

Tucson nestles among the Catalina, Rincon, Santa Rita, and 

Tucson Mountains, near the northern end of the upper Santa 

Cruz Valley. One hundred years ago, Tucson consisted of a 

few homes along the Santa Cruz River. Water was readily 

available from surface streams and shallow wells. But even then 

it was not cheap, and was sold by the cupful from goatskin bags 

and hide-lined barrels by street vendors.

The city is a few miles south of the confluence of the Santa 

Cruz River and the Rillito-Pantano drainage system, which receives surface flow from the Catalina and Rincon Mountains. 

Less than 1 percent of the precipitation falling in this area yields 

flood runoff, and local recharge to ground water is only a few 

thousand acre-feet annually. Much of the flood runoff in the 

Santa Cruz River evaporates or is transpired, and Tucson depends 

upon ground water to provide for its people, airbases, factories, 

and other enterprises. No surface water is used for municipal 

needs in the Tucson area, but a project has been proposed to 

direct flood runoff from Rillito Creek over a geologic barrier of 

impermeable rocks into Tucson's sandy ground-water reservoir.

Most of the city wells produce about 500 gpm each, but their 

range is wide. Withdrawals have been heavy in recent years, 

partly because of intermittent periods of severe drought and partly 

because of municipal expansion. The water table is declining 

in the Tucson area; the decline indicates that pumpage from 

storage exceeds natural replenishment.

Geologically, the alluvial deposits in the Tucson basin are 

typical of those in similar areas throughout the Desert Lowlands. 

Dense rock surrounds the basin on three sides. Lofty Mount 

Lemmon, 9,185 feet, is only 40 miles from the city. Alluvial beds 

constitute the ground-water reservoir in the Tucson basin. Local 

rock units vary in their water-yielding capacity, but the geology 

is complex and needs study to determine the amount of water 

that may be withdrawn.

Tucson plans eventually to obtain additional water from outside the urban area. This will entail additional expense for 

water transmission.

64
Flagstaff is fortunate in having surface-water as well as groundwater supplies. Located in the northern part of the Central 

Highlands, this community receives about 25 inches of precipitation annually. Water from Lake Mary has supplied the city for 

many years, but there were shortages in years when precipitation was low. At times during Flagstaff's early history, water 

had to be hauled in. Shortly after World War II, owing to 

population increase and scanty rainfall, the city had to develop 

additional supplies.

The information then available about ground water in the area 

was not encouraging. However, after an investigation by the 

U.S. Geological Survey, several exploratory holes were drilled. 

The study showed that both the Coconino Sandstone and the 

Supai Formation contain water at considerable depth and that 

both the amount of precipitation and the geologic environment 

were favorable for recharge of the ground-water supply. The 

mantle of permeable volcanic rocks and cinders allows water to 

percolate from the surface through the ground to the underlying 

sandstone. The investigation indicated that adequate water 

would be available in a fault zone southwest of the city. The first 

well produced about 300 gpm. Three additional wells on Woody 

Mountain produce 300 to 700 gpm. The water must be pumped 

from depths of more than 1,000 feet, however. Recharge conditions are very favorable in the newly developed well field, and 

natural replenishment along the fault zone assures long-term availability of water. Preliminary tests indicate that the fully developed 

well field may produce 5 to 6 mgd. Another 1.5 mgd in normal 

years is available from surface-water storage at Lake Mary. Thus, 

the community now has a dependable supply that is adequate for 

considerable growth and expansion.

The Safford area, along the upper Gila River in southeastern 

Arizona, includes the towns of Safford, Solomon, Central, Pima, 

and Thatcher. These municipalities obtain water from streams 

and wells. As population increases, increased demands are met 

by sinking new wells. Nearby river water cannot be tapped because downstream users have prior rights to the water.

Safford's municipal system obtains ground water from alluvial 

aquifers along Bonita Creek, a Gila River tributary. The watercollection system consists of an infiltration gallery 4 miles above 

the mouth of Bonita Creek. This gallery provides 900 to 2,500

65
acre-feet annually. Small emergency supplies are available from 

wells near the mouth of Bonita Creek. Water from the Safford 

wells is poor in quality. Surface water impounded by a small dam 

on the northeast slope of Mount Graham provides another emergency supply, but water from this source is not dependable because 

of the wide variations in surface runoff.

Safford is cooperating with the Geological Survey in an effort 

to develop additional water in the volcanic rocks along Bonita 

Creek. Currently, the city is engaged in a drilling program to 

develop additional water supplies from wells above the infiltration 

gallery on Bonita Creek.

At San Manuel on the San Pedro River, water for a recently 

developed copper mine, mill, smelter, and townsite is obtained 

entirely from wells. About 4,000 gpm is pumped from six 1,000- 

foot wells in valley-fill deposits near the river. About 350 gpm is 

distributed to the town for domestic and public use. The remainder, supplemented by 3,000 gpm pumped from San Manuel 

mine, is used for mill and smelter operations.

Water management at the San Manuel mine is a good example 

of efficiency in water use. All water pumped from the mine is 

put to use, and waste water from tailings and other sources is 

recirculated. Wells along the river are pumped to produce makeup water equivalent to less than 25 percent of the amount needed 

to operate the plant.

A recent study of the geology and ground water of the Hopi 

and Navajo Reservations was started by the Geological Survey 

in cooperation with the Bureau of Indian Affairs. The geologic 

work was hardly under way in 1950 when drought occurred. A 

well-drilling program was begun immediately. About 300 wells 

were drilled in 7 years, and as geologic knowledge of the reservations increased, the proportion of dry holes decreased, and the 

percentage in 1957 was practically zero. Some of the deepest 

wells tap water under artesian pressure, and in some the pressure is 

great enough to cause the wells to flow.

The yields of all wells are low. A yield of 200 gpm is high for 

this area. Commonly, the yields average 10 to 15 gpm, but these 

are adequate for present domestic and stock supplies.

Today the water requirements on the reservations are being 

met by development of ground water through geologic exploration. Water supplies developed with the aid of geologic informa66
tion have resulted in the establishment of industrial plants on the 

reservations.

Manufacturing and mining have increased considerably in the 

State in recent years, and demand for water has consequently increased. Total demand is small, however, compared to industrial 

demands in other parts of the Nation. In 1963, industry, including mining, used about 200,000 acre-feet of ground water in 

Arizona. This represents a 500 percent increase since 1949. 

The main water use in manufacturing is for cooling and sanitation, and only about 10 to 15 percent of the water used is consumed. The remaining 85 to 90 percent is available for reuse.

Assurance of a permanently adequate water supply is essential to 

an industrial plant. Treatment of water enables some industries to 

use water that in its native condition is unsuitable. Improved 

technology permits economical treatment of water that formerly 

could be treated only at prohibitive cost.

For industry the acceptable amount of dissolved solids in water 

ranges widely. Water for brewing, for example, may contain as 

much as 1,000 ppm of dissolved solids, where for candy-making, 

it should contain no more than 100. Calcium, magnesium, sodium, bicarbonate, sulfate, and chloride are the predominant constituents in most untreated water. The amounts of these various 

constituents determine whether or not it is suitable for specific 

industrial needs. Hardness, defined as the soap-consuming property, probably is the most familiar chemical characteristic of water. 

In some manufacturing processes, hardness can cause considerable 

trouble. The formation of scale in boilers is an example. Hardness is not the problem it once was in washing, however, now that 

synthetic detergents have come into widespread use.

Much of the water used by industry for cooling, separation 

processes, and other nonconsumptive operations is available for 

reuse. But nearly all uses of water cause at least some deterioration in its quality. Many kinds of use warm the water, and this is 

to be considered a form of pollution. Warm water may kill fish 

and water plants. Many manufacturing processes add contaminating chemicals to the water. However, industrial pollution of 

water so far is a minor problem in Arizona, except in certain local 

instances.

Recreational facilities for water sports are greatly in demand as 

a result of the growth in population, the increasing number of

67
vacationing tourists, and more leisure time for more people. Water-based recreation now appears to be more popular than ever 

before and to be expanding faster than any other kind of sport. 

In States such as Florida and Minnesota, water-based recreation 

can depend on thousands of miles of natural shoreline on lakes, 

streams, or the ocean. But in Arizona and other States in the 

Southwest, relatively few natural lakes can be found. Where they 

exist, they are often at very high altitudes 4,500 feet or more. 

A simple tally of reservoirs can almost sum up the easily accessible 

bodies of water available for recreation in Arizona. However, 

those in search of water-based recreation are not deterred by the 

scarcity of natural lakes. To enjoy their favorite sports, they will 

drive hundreds of miles to a reservoir, many carrying boats with 

them. Tourism now ranks third among the State's industries.

Speed-boating, Lake Mead Recreational Area.

More than 17 million acres of land in Arizona is owned for all 

the people by the Federal Government. Most of this Federal land 

is available for recreation, although little of it has been developed 

for this purpose. Colorful desert and deep mountain forests in 

the care of the National Park Service are available for people trying to "get away from it all." Lake Mead behind Hoover Dam is

68
the largest artificial lake in the world, with a shoreline of 550 miles; 

other, smaller reservoirs Mohave, Imperial, Roosevelt, Apache, 

Sahuaro, Lyman, San Carlos are used for water-based recreation. Lake Powell, formed by the giant Glen Canyon Dam, is 

rapidly rising and extending upstream; the Glen Canyon National 

Recreation Area will attract thousands of sportsmen and vacationers. Many other recreation areas in Arizona are administered 

by the State or operated by private enterprise. Every year more 

Americans are visiting Arizona in search of sunshine, sport, and 

a rest from the sights and sounds of crowded cities.

Many of these artificial lakes are stocked with fish from the 

State's hatcheries, and of course fishing is excellent in Arizona's 

mountain lakes and streams. White River and lakes and streams 

in the mountains offer fine sport for the fisherman. Because 

Arizona's larger rivers have been so drastically modified by dams 

and reservoirs, State and Federal agencies are working to 

protect the fishery potential and develop it further. Desirable species must be introduced into the artificial lakes; access

Fishing below Davis Dam on the lower Colorado.

69
must be provided for fishermen; and the problems of multiple 

recreational use must be solved.

If the population of Arizona continues to grow as trends indicate, more recreational reservoirs will be needed, as well as wetlands and bodies of water for propagating waterfowl and fish for 

the hunters and fishermen. The first and biggest problem will 

be obtaining sufficient supplies of water of suitable quality. Other 

problems follow in the wake of that one. Recreational use of a 

body of water implies at least a minimum standard of quality, 

both sanitary and esthetic. On the basis of this standard, recreational use of water may not be compatible with other uses, such 

as disposal of wastes, navigation, and waterpower. Some of the 

recreational uses conflict with each other. Motorboats and water 

skiers can be a menace to swimmers, and most types of water 

sport interfere with fishing in the same area. Recreational waters 

may have to be, and sometimes are, zoned to prevent such 

conflicts.

The benefits derived from recreational use of water are mostly 

intangible ones. It is difficult, if not impossible to assess the economic value of water for recreation. However, maintenance of 

sanitary standards, installation of docks and ramps, and supervision of public use all cost money. In water-hungry States, individuals are willing to pay for the privilege of using these facilities, 

as the revenues collected by Water Districts, National Park Service, and National Forest Service attest. For whatever purpose 

new reservoirs are constructed in the future, their use for recreation 

will have to be considered.

Some results of present use

The greatest demand for water in the State occurs in the Desert 

Lowlands in the southern part of the State. About 80 percent of 

the population and more than 90 percent of Arizona's irrigated 

acreage are concentrated here. During 1963, according to the 

Geological Survey's "Annual Report on Ground Water in Arizona," water levels in nearly all the developed basins in this part 

of the State continued to decline. As in past years, the greatest 

declines again occurred in the Salt River Valley, in Maricopa

70
County, and in the lower Santa Cruz River basin. Lesser declines of the water table occurred in other areas.

Observation wells in the irrigated areas of Arizona continued to 

record falling water levels. In the Salt River Valley during the 

5-year period 1958-63, the water level declined as much as 60 

feet. Other areas recorded similar sharp water-level declines. In 

the Eloy area the maximum 5-year decline was about 60 feet, and 

in the Stanfield-Maricopa area, about 100 feet. The Casa 

Grande-Florence area receives supplies of surface water from the 

Gila River (168,000 acre-feet in 1963); nevertheless, the groundwater level declined 40 feet in the 5-year period 1958-63. In 

the Kansas Settlement area of the Willcox basin, the decline 

in the year 1962-63 alone was as much as 50 feet.

A serious side effect of the decline of water levels due to intensive 

pumping is land-surface subsidence. Land subsidence or sinking 

has been suspected for some time in Arizona, but has now been 

confirmed in the Eloy area of Final County. Measurements indicate that by 1960 the land surface had sunk more than 3.5 feet 

along the Southern Pacific railroad 2 l/z miles northwest of Eloy. 

Nearly all this subsidence took place after 1934, during the period 

of ground-water development. Canals, bridges, and other structures that require a level grade can be seriously affected by 

subsidence.

Waterlogging is still another ground-water problem of recent 

significance, but rather different from most of Arizona's water 

problems. In areas where irrigation water is diverted from the 

Colorado River, water levels have risen. For example, in the 

Yuma Mesa area, water levels in wells rose 1 to 4 feet in 1960-61. 

A ground-water mound has developed beneath the mesa, making a drainage system, necessary. Nine drainage wells werfe 

installed in 1961, and water levels now are declining slightly. 

In the same way, the water levels in the Wellton-Mohawk area 

rose as much as 24 feet from 1956 to 1961. The resultant waterlogging made it difficult to grow crops successfully. A network 

of drainage wells was established in 1961 to pump the surplus 

water, which is then discharged to the Gila River, and water 

levels are declining.

681-100 O-66 8 71
THE 

FUTUR

Without large-scale water development, Arizona's wealth 

would be centered chiefly in livestock and mining, and each would 

operate on a much smaller scale than it does now. With water 

development, the personal income of Arizonians passed the 

$3.1 billion mark in 1962, according to the Valley National Bank. 

Development of water supplies contributes materially to the State's 

prosperity, which is based on agriculture, livestock raising, manufacturing, mining, and tourism. Perhaps of more importance, the 

availability of water helps to stabilize a diverse and well-rounded 

arid-land economy.

Of all the States, Arizona has had the largest percentage gain 

in population in the 20th century. In 1963 the population of 

Arizona was 1,545,000 a gain of nearly 76 percent in 10 years. 

According to students of population trends, this figure will increase to more than 2 million by 1975.

The available labor force, coupled with the natural advantages 

of the State, will attract industry at an increasing rate. This will 

be largely dry industry, an example of which is the electronics

72
manufacturing that has developed in Phoenix and Tucson. The 

phenomenal growth in manufacturing is due to several factors: 

inland location away from target areas, a reserve of skilled labor, 

and a dry climate. In some manufacturing processes, humidity 

control is very important.

The number of retired persons seeking to move to Arizona may 

increase. One of the first planned retirement communities was 

established at Youngtown, Ariz. Since then they have been organized in other parts of the State. One problem in Arizona is 

land acquisition. Over 85 percent of Arizona land is publicly 

owned, and patented lands amount to less than 8 acres per person, 

considerably below the national average.

Estimates of the population in the year 2000 range from 8 to 14 

million! Of course, even if these forecasts are reliable, population 

growth alone does not ensure prosperity. Capital must be invested and employment assured. According to recent studies, 

Arizona leads the Nation, not only in rate of population growth, 

but also in rates of income growth, employment growth, farmincome growth, and manufacturing growth.

Predictions of future municipal and industrial water demand 

vary widely, depending on estimates of future population and 

industrial development and estimates of per capita use. By 1975, 

if per capita use remains constant, municipal and industrial water 

demand is expected to double, but if per capita use continues to 

increase at its present rate, this demand may be about 1 million 

acre-feet per year.

How will enough water be obtained?

Surface waters are intensively used already, mostly for agriculture. Ground water is also being intensively developed. Continued depletion of ground water will probably lower water levels 

gradually, until the water is so deep that it would cost more to 

pump than could be regained by selling the crops the water irrigated. Because of declining water levels, farmland is being converted to residential tracts and industrial plots in the Salt River 

Valley. The finest agricultural land in the valley, including citrus 

and date groves, is becoming subject to the bulldozer. This does 

release irrigation water for domestic use and acre for acre 

domestic uses consume less water than agricultural uses. However, as more desert areas are developed, the demand for water in

73
these more than compensates for any additional water released 

from agricultural use.

Some studies show that water produces more wealth when used 

to support people and industry than when it is used for agriculture, 

but this may vary depending on local conditions. In water-short 

areas, competition for water is keen, and the long-term advantage 

rests with water uses that yield the greatest financial return.

In recent years, dry industry has become important in Arizona's 

economy. Dry industry needs water only for air conditioning and 

sanitary purposes. The amount of water needed to irrigate an 

acre of land for farming might meet the needs of a large factory 

where many persons work. Industry can probably obtain this 

water from deep wells, while a farmer might find the same water 

too expensive because of high pumping costs. The gross return 

from agriculture averages about $50 for each acre-foot of water 

used. Even with crops of the highest cash return, $14 is often 

considered to be about as much as agriculture can spend per acrefoot on water. On the basis of average dollar yield, industry in 

many areas is capable of paying a higher price for water than 

agriculture.

The cost of municipal water ranges widely throughout the State. 

Retail prices in most communities are between 25 cents and 1 

dollar per thousand gallons. In many areas, especially in the 

north, the cost of obtaining water for domestic and livestock purposes is high. Several municipalities have increased their water 

rates because of rising costs, and this trend will probably continue. Currently, a few communities charge from $1.00 to $1.80 

per thousand gallons. In one town, to which water is hauled, 

the price is $3.25 per thousand. Price per acre-foot ranges between $80 and $320 in most Arizona communities.

The vital need for additional water in Arizona is recognized by 

most of its citizens. If additional water cannot be obtained, the 

alternatives are continued depletion of the ground-water reservoir, 

or reduction in water use (with consequent possible dislocations in 

the economy), or more efficient and conservative use of the available supply. Of these alternatives, logic points to the last one.

Several methods have been proposed to reduce or prevent water 

waste. An intensive program of watershed management might 

salvage some water by removal of nonbeneficial vegetation. Wil74
low, saltcedar, and other trees that line creeks are major water 

users.

It is not easy to eradicate saltcedar. Burning does not destroy 

the roots, and next year's growth is more vigorous. Chemical 

agents of destruction tend to get into ground water and endanger 

water supplies near stream channels. Chopping saltcedar down 

activates the soil, reduces overgrowth, and encourages young vigorous growth in succeeding seasons.

One efficient method of destroying saltcedar is to lower the 

water table quickly beyond reach of its roots. In the Gila River 

below Gillespie Dam, large areas of nonbeneficial plants have had 

their water supply reduced by a rapid drop in the water table, and 

the growth is much thinner than it used to be. Such a remedy, 

however, cannot be practically applied over the whole State.

The watershed-management program might include eradication of juniper and pinon, thinning stands of ponderosa pine, cutting among the spruce and fir to reduce transpiration of water, 

and eradication of chaparral. Cleared areas would be seeded to 

grass in the hope that grass will eventually cause a smaller evaporation loss than did the woodlands. However, modification of native vegetation brings its own problems, which would have to be 

considered. In any event, large-scale eradication programs might 

best be deferred until research data now being collected are available to provide a basis for forecasting the actual results of such 

measures.

Nonbeneficial water-loving vegetation on the Gila River.

fe?
£

,-sga

Saltcedar along the Gila River.

Control of evaporation is another method of water conservation. Arizona has more than 17,000 miles of mapped stream 

channels. Some channels are in narrow gorges in impervious 

rock; others are underlain by porous sand and gravel in broad 

open valleys. Some streams flow continuously; others flow infrequently and only immediately after rain. Many miles of additional channels are not shown on maps. A large number of 

valleys are barren; others are choked with water-loving plants. 

Between these two extremes are an infinite number of conditions. 

However, there is one common characteristic of channels in Arizona large amounts of water are lost through evaporation.

Concurrent records of streamflow on the Gila River at Gillespie 

Dam and at Dome are available since 1921. When compared, the 

records of annual runoff at the two sites give some idea how much 

water is evaporated. The greatest recorded loss, 600,000 acrefeet, occurred in 1941. Most of this water was evaporated, but of 

course unknown amounts were transpired or contributed to 

recharge.

76
Laboratory research suggests that evaporation from the surface 

of reservoirs, at least, can be reduced under some circumstances by 

more than 25 percent through the application of a chemical film. 

Research is now underway both to improve methods and to evaluate results. There is some evidence that the treatment is more 

practical on small than on large bodies of water. If this is confirmed by further work, evaporation control may have applicability to the thousands of small reservoirs and ponds throughout the 

State. In addition, evaporation reduction can be achieved by 

careful location and design of new reservoirs. It is well established, for example, that a deep pond of small surface area loses 

less water by evaporation than a wide shallow pond of the same 

capacity. Because deep tanks retain water longer, they also serve 

the rancher better.

One of the most practical ways to increase the availability of 

water supplies is to capture water and put it underground. Floodwaters as well as base flow could be captured and transported by 

lined canals or conduits to the areas of need, for example, where 

ground-water withdrawals have been large. The water could then 

be recharged into dewatered sediments by means of wells (fig. 22).

 _, c < j *" - *xr* * * '^>^_

Figure 22. Using wells for artificial recharge.

77
Many engineering, geologic, legal, and economic problems 

would have to be solved to make this method practical. Amounts 

of water that could be salvaged and points of most efficient impoundment would have to be determined. The water might have 

to be desilted before it is fed underground. Experiments in Texas 

and elsewhere indicate that silt allowed to go underground tends 

to seal the surrounding material and reduce a well's intake capacity. Chemical reactions also tend to reduce capacity.

Desalination of brackish water would provide another source 

of water supplies. Cost of conversion is presently about 15/2 times 

the cost of present-day municipal water in Arizona. But for some 

uses the cost of converting the brackish ground-water reserves 

may not be an impossible obstacle.

To achieve any of these salvage methods, some measure of 

State or local responsibility would be necessary. At present, the 

ground-water resource continues to be exploited without any particular management other than the water users' needs at the 

moment. Attempts to control ground-water draft by legislation 

have been unsuccessful. The State legislature has restricted the 

drilling of wells to supply new irrigation developments in four 

"critical areas," but heavy pumping continues in these. New 

developments have been started in other basins, despite the prospect of eventual depletion.

The interrelation of surface and ground water must be recognized, and the technique of joint management developed. To 

this end, the laws governing water rights may have to be modified. 

Most water law developed at a time when the science of hydrology was little understood, and the law has not kept abreast of 

scientific advances.

One legal development of great importance was the ruling of 

the Secretary of the Interior in 1961 withdrawing from entry of 

certain desert lands in the public domain. This will tend to limit 

development in public lands and thus not add still further drafts 

on heavily used ground-water resources.

Another major step needed is basinwide management planning of the water resources, both surface and ground water. This 

need is especially critical in the Gila, Salt, San Pedro, and Santa 

Cruz River valleys where the greatest overdevelopment has taken 

place and where most of the ground-water basins are intercon78
nected in varying degrees. Hydrologic studies on a basinwide 

basis would be required in support of the planning program. A 

recent innovation in ground-water studies that can be of great 

assistance in basinwide planning is the electric-analog model. 

Such models duplicate the hydraulic regime effectively on a laboratory scale. This makes it possible to try various alternate 

solutions to a given problem without the time and expense of 

extensive field tests.

For many years Arizona has pursued a course of depletion of its 

ground-water reserves. The Nation has followed exactly the same 

course in regard to its oil resources. Without controls on 

production or well spacing, each oil producer tried to produce as 

much oil as possible as soon as possible, before the oil was exhausted. Presently the ground-water resource is being exhausted 

at a rate greater than it is being replenished. Yet utilization of 

the resource is an indispensable part of the State's economy. Unplanned, rapid depletion of ground-water storage, however, can be 

very inefficient. Rapid depletion results in rising power costs 

owing to increased pumping lift and in excessive maintenance costs 

owing to the need for frequent lowering of pumps and deepening 

of wells. Land subsidence is another common result of overdraft 

of ground water.

Planned management of ground-water development can soften 

or prevent a blow to the local economy. Now may be the time to 

decide whether to continue the unregulated and haphazard development of this resource or to modify and regulate it.

We need information on the present total supply, the extent of 

the reserves, and the rate of depletion that will provide the most 

efficient exploitation. We need a better understanding of the 

hydrologic system, and the physics, or mechanics, of water movement. All the disciplines in water resources should be harmonized 

and merged to achieve a clear understanding of Arizona's hydrologic system.

After the magnitude of the total supply is known, some questions that are difficult to answer still remain. What will be the cost 

of water? What economic pursuits will be able to pay the price? 

What will happen when the water level drops down to the impervious layers or lakebed deposits? Some of these questions cannot 

be answered; others require information about the occurrence of

79
water itself. The hydro! ogic data should be studied, analyzed, and 

interpreted so that management will have sound information on 

which to base decisions. As Secretary Udall has said before the 

American Water Works Association, Philadelphia, Pa. (June 20, 

1962):

Neither new laws nor new planning groups will create water where none 

existed before, or restore it where it has been mined; nor will they restore the 

quality of water that has deteriorated. Neither new laws nor new development schemes will necessarily prevent the consequences of bad management. 

The first need is not new regulations, but intelligent management.

History contains documented accounts of many civilizations that 

attained a high degree of progress, but declined or even became 

extinct when their water supplies were exhausted. Several notable 

examples are in the Middle East. The facts in the lesson are clear; 

however, Arizona need not suffer a similar decline in productiveness. Armed with a knowledge of water resources, informed citizens will be better able to plan for and evaluate prudent water 

management in Arizona.

80
FOR MORE INFORMATION 

ABOUT 

Basic Water Facts, Principles, and Problems:

A primer on water, by L. B. Leopold and W. B. Langbein, a special report by the U.S. Geological Survey: 

Washington, D.C., U.S. Government Printing Office, 

50 pages, 1960.

A primer on ground water, by H. L. Baldwin and C. L. 

McGuinness, a special report by the U.S. Geological 

Survey: U.S. Government Printing Office, 26 pages, 

1963, reprinted 1964.

National water resources and problems, by R. E. Oltman 

and others: U.S. Senate (86th Congress, 2d session) 

Select Committee on National Water Resources, Committee Print 3, Washington, D.C., U.S. Government 

Printing Office, 42 pages, 1960.

Arizona, its people and resources, edited by Jack L. Cross, 

Elizabeth H. Shaw, and Kathleen Scheifele: Tucson, 

Ariz., The University of Arizona Press, 385 pages, 1960.

Progress report of the committee on quality tolerances of 

water for industrial uses, by E. W. Moore: Journal 

New England Water Works Association, volume 54, 

271 pages, 1940.

Ten rivers in America's future: Report of the President's 

water resources policy commission, volume 2, 801 

pages, 1950.

81
Arizona Resources:

The Colorado River, Proposed report of the Secretary of 

the Interior: Bureau of Reclamation, U.S. Government 

Printing Office, 295 pages, 1946.

Bill Williams River and tributaries, Arizona: 78th Congress, 2d session, House Document 625, U.S. Congress, 

House Committee on Food Control, 29 pages, 1944.

The Hoover Dam Documents, by R. L. Wilbur and 

Northcutt Ely: 80th Congress, 2d session, House Document 717, 936 pages, 1948.

The Technical and Scientific Background:

Annual report on ground water in Arizona: Arizona 

State Land Department, Water resources reports.

Analysis of basic data concerning ground water in the 

Yuma area, Arizona, by R. H. Brown, J. W. Harshbarger, and H. E. Thomas: U.S. Geological Survey 

open-file report, 117 pages, 1956.

Erosion and sedimentation in the Papago country, Arizona, with a sketch of the geology, by Kirk Bryan: U.S. 

Geological Survey Bulletin 730-B, pages 19-90, 1923.

Soil salinity problems along the Rio Grande in New 

Mexico and Texas, by C. W. Chang, in Problems of the 

upper Rio Grande: International Arid Lands Symposium and Conference, held in 1955 at University of 

New Mexico and New Mexico Institute of Mining and 

Technology, U.S. Commission for Arid Resource Improvement and Development Publication 1, page 5, 

1957.

Significance of carbonates in irrigation waters, by F. M. 

Eaton: Soil Science, volume 69, pages 123-133, 1950.

Use of water by bottom-land vegetation in lower Safford 

Valley, Arizona, by J. S. Gatewood, T. W. Robinson, 

B. R. Colby, J. D. Hem, and L. C. Halpenny: U.S. 

Geological Survey Water-Supply Paper 1103, 210 

pages, 1950.

82
Diagnosis and improvement of saline and alkali soils, by 

L. A. Richards and others: U.S. Department of Agriculture Handbook 60, 160 pages, 1954.

Phreatophytes, by T. W. Robinson: U.S. Geological Survey Water-Supply Paper 1423, 84 pages, 1958.

Rainfall and runoff in the upper Santa Cruz drainage 

basin, by H. C. Schwalen: University of Arizona, Arizona Agricultural Experiment Station Technical Bulletin 95, pages 421-472, 1942.

Water in the Santa Cruz Valley, by H. C. Schwalen and 

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by S. F. Turner and others: U.S. Geological Survey 

open-file report, 84 pages, 1943.

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Basin, Arizona, by S. F. Turner and others: U.S. Geological Survey open-file report, 28 pages, 1946.

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County, Arizona, by S. F. Turner and H. E. Skibitzke: 

American Geophysical Union Trans., volume 33, 

number 1, pages 66-72, 1952.

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reconnaissance of parts of Arizona, New Mexico, and 

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U.S. Geological Survey open-file report, 224 pages, 

1952.

Use of ground water in Arizona, by J. W. Harshbarger, in 

Climate and man in the Southwest : Contribution 6, 

Program in Geochronology, University of Arizona 

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83
The Navajo country, Arizona-Utah-New Mexico, by 

J. W. Harshbarger, C. A. Repenning, and J. T. Callahan, in The physical and economic foundation of natural resources, Part 4, Subsurface facilties of water management, and patterns of supply Type area studies: 

House of Representatives, Interior and Insular Affairs 

Committee, pages 105-131, 1953.

Quality of water of the Gila River basin above Coolidge 

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Water-Supply Paper 1104, 230 pages, 1950.

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Magistaad and J. E. Ghristiansen: U.S. Department 

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Water levels and artesian pressures in observation wells 

in the United States, Southwestern states: U.S. Geological Survey Water-Supply Papers. 

84
Picture Credits

The Bureau of Reclamation, U.S. Department of the Interior, allowed use 

of the photographs on pages 10, 13, 19, 61, 62, 68, and 69; and National 

Park Service, U.S. Department of the Interior, lent the photographs appearing 

on pages 22, 23, and 25.

85

U.S. GOVERNMENT PRINTING OFFICE: 1966 O 681-100