The Rio GrandeThe Rio Grande flows through the Southwestern United States.

Rio Grande, (Mexican: Rio Bravo del Norte ), a North American river shared by the United States and Mexico. It begins in the Rocky Mountains of southwestern Colorado and flows southward through New Mexico to the western tip of Texas. From there the river flows southeastward to the Gulf of Mexico, forming the boundary between Mexico and the United States.

The Rio Grande is 1,900 miles (3,058 km) long and has a drainage basin of roughly 170,000 square miles (440,000 km 2). By the volume of its flow, however, the Rio Grande is not a major river. Most of the basin is arid to semiarid land, and the river's flow is relatively small and fluctuates greatly. The Pecos, in Texas, and the Conchos, in Mexico, are the chief tributaries.

The most important cities on the Rio Grande are Albuquerque, New Mexico; Reynosa, Mexico; and the twin border cities (in Texas and Mexico, respectively) of El Paso—Ciudad Jurez, Laredo—Nuevo Laredo, and Brownsville-Matamoros.

Shallows and sand bars make the Rio Grande unfit for navigation in most places. Water for irrigation, however, is extremely important, especially in the lower Rio Grande Valley, which is a major source of citrus fruits, winter vegetables, and cotton. Two large projects—Amistad Dam and Reservoir above Del Rio and Falcon Dam and Reservoir below Laredo—have been constructed jointly by the United States and Mexico since a 1945 agreement between the two countries to cooperate on irrigation and flood control. Irrigation on a lesser scale is made possible in southern New Mexico by Elephant Butte and Caballo dams and their reservoirs.

A large bend in the Rio Grande in southwest Texas is the site of Big Bend National Park, featuring spectacular mountain and desert scenery. Amistad National Recreation Area adjoins Amistad Reservoir.

History

Pueblo Indians settled parts of the northern Rio Grande Valley in pre-Columbian times, probably as early as the 13th century. Beginning in the early 1500's Spanish conquistadores explored the valley. Spanish settlements and missions eventually followed. The river's entire course ultimately came under Spanish control; in 1821 it became part of independent Mexico.

The Republic of Texas claimed the Rio Grande as its southern boundary in 1836; this claim resulted in a dispute that became one of the causes of the Mexican War. .) After the war, in 1848, the river was made the United States-Mexican border by the Treaty of Guadalupe Hidalgo. Because of occasional shifts in the course of the river, boundary disputes have occurred periodically.

Great devastation swept the lower Rio Grande Valley in 1967, when a powerful hurricane spawned tornadoes and cloudbursts that caused widespread flooding.