Known as the Rio Grande in the United States and as the Río Bravo (or, more formally, the Río Bravo del Norte) in Mexico, the river rises in the San Juan Mountains of Colorado, USA, flows through the San Luis Valley, then south into New Mexico through Albuquerque and Las Cruces to El Paso, Texas, on the U.S.–Mexico border.
The river has, since 1845, marked the boundary between Mexico and the United States from the twin cities of El Paso, Texas, and Ciudad Juárez, Chihuahua, to the Gulf of Mexico. As such, it was across this river that Texan slaves fled when seeking their freedom, aided by Mexico's liberal colonization policies and abolitionist stance.
The major international border crossings along the river are Ciudad Juárez and El Paso; Laredo, Texas, and Nuevo Laredo, Tamaulipas; McAllen-Hidalgo, Texas, and Reynosa, Tamaulipas; and Brownsville, Texas, and Matamoros, Tamaulipas. Other notable border towns are the Texas/Coahuila pairings of Del Rio–Ciudad Acuña and Eagle Pass–Piedras Negras.
Use of the water of the Rio Grande is regulated by the Rio Grande Compact, an interstate pact between Colorado, New Mexico and Texas; and a treaty between the United States and Mexico. The Rio Grande is over-appropriated, that is, there are more users for the water than there is water in the river. Since the summer of 2003, much of the river from Albuquerque to the Big Bend National Park has been dry. Ecologists fear that unless rainfall returns to normal levels during the next few years and strict water conservation measures are adopted by communities along the river, the Rio Grande may soon become extinct.
The Rio Grande rises in high mountains and flows for much of its length at high elevation; El Paso is 1147 m (3762 feet) above sea level. In New Mexico the river flows through the Rio Grande Rift from one sediment-filled basin to another, cutting canyons between the basins and supporting a fragile bosque ecosystem in its floodplain. From El Paso eastward the river flows through desert. Only in the sub-tropical lower Rio Grande Valley is there extensive irrigated agriculture. The river ends in a small sandy delta at the Gulf of Mexico. During periods of extended dry weather, the river will actually cease flowing into the Gulf.
Millions of years ago, the Rio Grande ended at the bottom of the Rio Grande Rift in Lake Cabeza de Vaca. But about 1 million years ago the stream was "captured" and began to flow east.
All text is available under the terms of the GNU Free Documentation License.