COLORADO RIVER

Physical features of western North America. major river of North America, rising in the Rocky Mountains of Colorado, U.S., and flowing generally west and south for 1,450 miles (2,330 kilometres) into the Gulf of California in northwestern Mexico. Its drainage basin covers 246,000 square miles (637,000 square kilometres) and includes parts of seven statesWyoming, Colorado, Utah, New Mexico, Nevada, Arizona, and California. For 17 miles the river forms the international boundary between the U.S. state of Arizona and Mexico. The river drains a vast arid and semiarid sector of the North American continent, and because of its intensive development it is often referred to as the Lifeline of the Southwest. Physical features of western North America. major river of North America, rising in the Rocky Mountains of Colorado, U.S., and flowing generally west and south for 1,450 miles (2,330 km) into northwestern Mexico. The Colorado River's drainage basin comprises 246,000 square miles (637,000 square km) in seven statesWyoming, Colorado, Utah, New Mexico, Nevada, Arizona, and California. For 17 miles (27 km) the river constitutes the international boundary between Arizona and Mexico and then intermittently flows 80 miles (130 km) through Mexico to the Gulf of California. It drains a vast, arid sector of the North American continent. No other river in the world has cut such a remarkable number of extremely deep trenches, of which the Grand Canyon (q.v.) is the largest and most spectacular. The Colorado is also remarkable in its value for hydroelectric power and irrigation. The river combines a large quantity of water, great concentrations of fall, reservoir sites for the control of flow, sites for hydroelectric-power plants, and several million acres of irrigable land below the stretch where power may be developed. For more than 1,000 miles (1,600 km) of its upper and middle course, the Colorado has cut a deep gorge, with an additional transverse system of deep, winding canyons where lateral streams join the river. On the lower course of the Colorado is the Mohave Desert, the Salton Trough (Salton Basin), and two subsections of the Sonoran Desert: the Colorado Desert (reaching the west bank) and the Yuma Desert (east bank). The Colorado River system was the first drainage basin in which the concept of multiple use of water was put into practice (e.g., power development, irrigation, recreation, and flood control). The first major development of the Colorado began in 1928, when Congress passed an act authorizing the construction of Boulder (now Hoover) Dam; this multipurpose water-storage project was a major engineering feat of its time (see Hoover Dam). Since its completion in 1936, the Hoover Dam and Lake Mead (q.v.), which it created with its impounded waters, have become major tourist attractions. Many additional projects have since been completed on the river, notably Glen Canyon Dam, impounding Lake Powell, and Parker Dam, impounding Lake Havasu, which supplies water for southern California. Other projects divert water from the Colorado River through tunnels and aqueducts to irrigate cropland in northern Colorado and to supply the cities of Phoenix and Tucson in Arizona. A desalinization plant at Yuma, Ariz., which opened in 1992, provides Mexico with potable water. More than 20 dams have been built on the Colorado and its tributaries, and, as a result of this, the river reaches the Gulf of California only intermittently. The Morelos diversion dam, which is located on the Mexico-Arizona border and is the southernmost dam on the Colorado, sends virtually all of the remaining water to the irrigation canals of the Mexicali Valley and to the Mexican border towns of Mexicali and Tijuana. river rising in western Texas, U.S., on the Llano Estacado (Staked Plain) in Dawson county, north of Lamesa. It flows generally southeast past Colorado City, through rolling prairie and rugged hill and canyon country, via the Highland Lakes past Austin, and across the coastal plain to enter Matagorda Bay (an inlet of the Gulf of Mexico) after a course of 862 miles (1,387 km). The river, the largest entirely within Texas, drains an area of about 39,900 square miles (103,350 square km) and receives several prongs of the Concho River, the Pecan Bayou, and the San Saba, Llano, and Pedernales rivers. It is the site of several important flood-control, power, irrigation, and recreational projects. Spanish Ro Colorado, river in south-central Argentina. Its major headstreams, the Grande and Barrancas rivers, flow southward from the eastern flanks of the Andes and meet north of Buta Ranquil to form the Colorado. The river flows generally east-southeastward across the arid terrain of northern Patagonia and the southern Pampas and is a border for four provinces. Its lower course splits into two arms, which flow into the Atlantic Ocean south of Baha Blanca. The total length of the Colorado is about 530 miles (850 km). Additional reading Philip L. Fradkin, A River No More: The Colorado River and the West (1981), is a lucid introduction describing the river from the headwaters to the delta. John Wesley Powell, Canyons of the Colorado (1895, reissued as The Exploration of the Colorado River and Its Canyons, 1987), is an exciting account of an early scientific exploration with a wealth of geologic and ethnographic detail. A broader context of exploration and settlement is provided in Richard A. Bartlett, Great Surveys of the American West (1962, reprinted with expanded bibliography, 1980); and William H. Goetzmann, Exploration and Empire: The Explorer and the Scientist in the Winning of the American West (1966, reissued 1978). William L. Graf, The Colorado River: Instability and Basin Management (1985), examines the physical geography of the basin, with emphasis on natural processes and the impact of human activity. National Research Council (U.S.), Committee on Water, Water and Choice in the Colorado Basin: An Example of Alternatives in Water Management (1968), remains a landmark study of river-basin management and policy. James L. Wescoat, Jr., Integrated Water Development: Water Use and Conservation Practice in Western Colorado (1984), describes how basinwide policies influence every aspect of water use in local areas. Gary D. Weatherford and F. Lee Brown (eds.), New Courses for the Colorado River (1986), combines a balanced review of historical controversies with creative approaches for addressing them in the future. James L. Wescoat, Jr.