RIVER BASINS OF THE UNITED STATES

COLORADO

U. S. DEPARTMENT F THE INTERIOR /GEOLOGICAL SURVEY

Facts about the

COLORADO RIVER BASIN EARLY EXPLORATION: Francisco de Ulloa, Spanish soldier and explorer, was probably the first white man to see the Colorado River. Several names were given to the river between 1540 and 1776 when Father Garces named it the "Rio Colorado." The name "Colorado" was not applied to the entire river until Congress did so in 1921.

HEADWATERS: River rises in Rocky Mountain National Park in north-central Colorado; becomes a perennial stream near Poudre Pass in Colorado.

MOUTH: Gulf of California, Mexico, at approximately 32° latitude and 115° longitude.

MAJOR TRIBUTARIES: Gunnison, White, Yampa, San Juan, Dolores, Green, Little Colorado, Gila, and the Virgin Rivers.

COURSE: From headwaters, river flows southwestward in a series of meanders, across the high Colorado Plateau into southeastern Utah and down through northwestern Arizona. It slashes through a wilderness of mountains, plateaus, and deserts; is cliff-bound nine-tenths of its way and travels 1,000 miles through deep canyons; Grand Canyon is the largest, deepest, and most spectacular. River then bends south to form the boundaries between Nevada and Arizona, and between Arizona and California. It flows into the Gulf after first forming the boundary between the Mexican States of Sonora and Baja. California.

LENGTH: Approximately 1,440 miles. Ranks 6th in length of 135 U.S. rivers that are more than 100 miles long. WIDTH: About 50 feet for the first 50 miles; 200 feet at Grand Junction, Colo.

DEPTH: About 30 feet in lower reaches of Grand Canyon; not more than 10 feet in upper reaches of river above Grand Junction.

RATE OF FLOW: Near Lees Ferry, Ariz.—about 8 million gallons per minute; at mouth— about 2 million gallons per minute.

HIGHEST AND LOWEST FLOW: In 1916, record flood at Yuma, Ariz. The lowest natural (unregulated) flow occurred at Lees Ferry in 1924.

QUALITY: River once was one of the most silt-laden streams in the U.S. but now reservoirs trap most of the sediment. Average salinity is less than 50 parts per million in headwater areas but exceeds 1,000 parts per million much of the time at the international boundary. There is little pollution from municipal and industrial wastes except in the immediate vicinity of cities and towns. Most of the ground water used for irrigation is not treated; that used for municipal supply is chlorinated.

DAMS, RESERVOIRS, AND CANALS: Flaming Gorge Dam in Utah; Navajo Dam in New Mexico; Glen Canyon Dam and Lake Powell in Arizona and Utah; Blue Mesa Dam in Colo-rado; Hoover Dam and Lake Mead, Davis Dam and Lake Mohave, and Parker Dam and Havasu Lake in Nevada, and Imperial Dam in Arizona.

GEOLOGIC SETTING: Basin lies in three physiographic provinces: Southern and Rocky Mountain, Basin and Range, and Colorado Plateau. About 240,000 square miles of Basin is arid to semi-arid. Colorado Plateau is composed of horizontal, sedimentary rock strata (sand-stone, limestone, shale, conglomerate) which have been uplifted thousands of feet, faulted, and carved by erosion into broad plateaus, mesas, buttes, natural bridges, and deep canyons. Colorado Desert in the southwestern part of the Basin is extremely arid and hot. Most of it is below sea level.

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facts cont'd

DRAINAGE AREA: Basin area in the United States is 243,000 square miles; includes parts of Wyoming, Colorado, Utah, New Mexico, Nevada, Arizona, and California.

AVERAGE RAINFALL: About 15 inches annually over most of the Basin; from 5 in' 14t's Arizona deserts to more than 50 inches in Colorado Mountains.

FIRST SETTLEMENT: Prehistoric race called Hohokam lived and vanishe0 in Salt Valley before Hopi and Pueblo Indians inhabited the area. Father Eusebio Kino established Jesuit missions in 1700 at San Xavier Del Bac and in 1732 at Guevavi, both in Arizona. In 1776 the first white settlement was established near present-day Tucson.

MAJOR CITIES: Phoenix, Ariz. is the largest city in the Basin. Cities of lesser size are Duch-esne and Moab, Utah; Grand Junction, Colo.; Boulder City and Las Vegas, Nev.; Tucson and Yuma, Ariz.; Needles, Calif.

MUNICIPAL AND INDUSTRIAL WATER USE: Limited because Basin is sparsely populated. (One of the least populated areas of its size in the Western Hemisphere.) Principal uses of river are for hydro-electric power and irrigation. Irrigation consumes nearly the entire flow. In addition to uses within the Basin, large quantities of water are diverted to adjacent river basins for municipal, industrial, and irrigation uses. About 2 million people in the Basin use approximately 400 million gallons of publicly supplied water each day and about 1A of a million people in rural areas use approximately 25 million gallons of water each day.

COMMERCIAL WATER USE: In addition to flood control, the river and its dam system provide facilities for irrigation, hydro-electric power, and recreation in the form of boating, fishing, skiing, and swimming.

AGRICULTURE: Fruits, some cotton, grazing, and general farming. Irrigated agriculture practiced in every State in Basin.

INDUSTRY: Little industrial development except light industry in the Phoenix, Ariz. area.

MINERALS: Uranium, zinc, silver, molybdenum, copper, gold, lead, coal, petroleum, and oil shale.

BASIC WATER DATA

The Hydrologic Data Network, maintained by the U. S. Geolog-ical Survey in cooperation with the individual States, is the chief source of basic data on water in this country. The Geological Survey and its cooperators main-tain a stream-gaging network of more than 8,400 stations, a ground-water network of about 16,000 observation wells, and more than 2,200 water-quality stations.

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