Gila

River rising in the Black Range in southwestern New Mexico, USA, and flowing west across southern Arizona, south of Phoenix, to join the Colorado River, of which it is the major tributary; length 1,045 km/650 mi. The Gila and its tributaries are an important source of irrigation water in an arid area; produce includes cotton and fruits.

Course The river rises near the Gila Cliff Dwellings National Monument in the Gila National Forest, Catron County. In southeast Arizona it passes through Safford, the San Carlos Apache Reservation (site of the Coolidge Dam), and Florence. Passing between the Casa Grande and Phoenix areas, it proceeds west, then sharply south to Gila Bend and the Painted Rock Reservoir. It then winds west-southwest and joins the Colorada at Yuma.

Tributaries Its tributaries include the San Simon, San Pedro, and Santa Cruz, which join it from the south in Arizona; and the Salt, Agua Fria, and Hassayampa, which join it from the north. Today the Gila, Salt, and other rivers in the system have been dammed, and both the mainstream and tributaries flow intermittently.

History Before 1854 the Gila formed the Mexican-American boundary; the Gadsden Purchase then transferred to the USA lands south of the river, an area still heavily Mexican, Apache, Pima, and Tohono o'Odham (Papago) in influence.