The Rio Grande (called the Río Bravo or, more formally, the Río Bravo del Norte in Mexico) is a river which rises in the San Juan Mountains of Colorado, flows through the San Luis Valley, then south into New Mexico through Santa Fe, Albuquerque and Las Cruces to El Paso, Texas on the border with Mexico.
Major cities along the border are Ciudad Juarez, Mexico across the river from El Paso; Laredo, Texas and Nuevo Laredo, Mexico; and Brownsville, Texas and Matamoros, Mexico. Other notable towns along the river are Del Rio and Eagle Pass, both in Texas.
Use of the water of the Rio Grande is regulated by the Rio Grande Compact, an interstate compact 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 several years, and strict water conservation is adopted by communities along the river route, 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 3762 feet above sea level. While in New Mexico the river flows through the Rio Grande Rift from one sediment filled basin to another, cutting canyons between the basins. Anciently the Rio Grande terminated at the bottom of the Rio Grande Rift in Lake Cabeza de Baca. About 1 million years ago the stream was "captured and began to flow eastward. 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 on the Gulf of Mexico.