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Gila River

River in New Mexico and Arizona, United States

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View of the Gila Box Riparian National Conservation Area — in southeastern Arizona. Sonoran Desert "xeric" riparian habitat , located along the eastern Gila River .
BLM · Public domain

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Through Tributary, Stream and Irrigation

Indigenous peoples have lived along the river for at least 2,000 years, establishing complex agricultural societies before European exploration of the region began in the 16th century. European Americans did not permanently settle the Gila River watershed until the mid-19th century.

During the 20th century, development in the Gila River watershed prompted the construction of large diversion and flood control structures on the river and its tributaries, consequently the Gila contributes only a small fraction of its historic flow to the Colorado. The historic natural discharge of the river was around 1,900 cubic feet per second (54 m3/s), but has declined to only 247 cubic feet per second (7.0 m3/s). The engineering projects transformed much of the river valley and its surroundings from arid desert into irrigated land, and supply water to more than 6 million people in the Phoenix and Tucson metropolitan areas who live in the watershed.

Geography

The Gila River has its source in western New Mexico, in Sierra County on the western slopes of the Continental Divide in the Black Range. It flows southwest through the Gila National Forest, the Gila Wilderness, and Gila Cliff Dwellings National Monument, then westward into Arizona, past the town of Safford. After flowing along the southern slope of the Gila Mountains in Graham County through a series of canyons, the Gila is impounded by Coolidge Dam in San Carlos Lake south of Peridot.

It emerges from the mountains into the valley southeast of Phoenix, Arizona, where it crosses the Gila River Indian Reservation as an intermittent stream due to large irrigation diversions, primarily at the Hayden Ashurst Diversion Dam. Well west of Phoenix, the river bends sharply southward along the Gila Bend Mountains, then swings westward again near the town of Gila Bend. It flows southwestward between the Gila Mountains to the south and the Languna and Muggins ranges to the north in Yuma County, and finally it empties into the Colorado at Yuma, Arizona.

The Gila is joined by many tributaries, beginning with the East and West Forks of the river, which combine to form the main stem near Gila Hot Springs in New Mexico. Above Safford, it is joined by the San Francisco River and the intermittent San Simon River. Further downstream, it is joined by the San Carlos River from the north in San Carlos Lake. At Winkelman, Arizona, it picks up the San Pedro River and then is joined by the Santa Cruz River south of Casa Grande. The Salt River, its main tributary, joins in the Phoenix metropolitan area, and further west the Gila receives its last two major tributaries, the Agua Fria and Hassayampa Rivers, from the north.

Although the Gila River flows entirely within the United States, the headwaters of two tributaries – the San Pedro and Santa Cruz Rivers – extend into Mexico. About 1,630 mi2 (4,200 km2), or 2.8% of the Gila's 58,200-square-mile (151,000 km2) watershed, is in Mexico. A further 3,300 mi2 (8,500 km2) or 5.7% lies within New Mexico, while the remaining majority, 53,270 mi2 (138,000 km2) or 91.5%, is in Arizona.

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