The Middle Rio Grande Valley
The state of New Mexico contains three distinct river systems: the Rio Grande, the Canadian River, which eventually drains into the Mississippi, and the San Juan and Gila rivers, which both drain into the Colorado. A fifth major river, the Pecos, drains into the Rio Grande in Texas and so is considered part of that system. Numerous smaller rivers and creeks all drain into one of these systems, or in a few cases into closed basins with no outflow. The Rio Grande is the dominant river system in New Mexico in terms of the area of its watershed, or the area of land from which water drains into the river.
Follow this link to The Upper Watershed for a more thorough explanation of watersheds.
In total, the Rio Grande stretches about 2000 miles (3220 km) from its headwaters along the Continental Divide in the San Juan Mountains of southwestern Colorado to its outflow into the Gulf of Mexico near Brownsville, Texas and Matamoros, Mexico. Along the way, the Rio Grande passes through three states in the United States and four in the Republic of Mexico. The Rio Grande, known as the Rio Bravo in Mexico, forms the international boundary between Texas and Mexico.
Follow this link to view a map of the Rio Grande Basin.
In the guide we focus on what is known locally as the Middle Rio Grande Valley. This name is a bit misleading, for it does not represent the actual "middle" of the river, but rather refers to the approximate middle of the portion of the river that passes through New Mexico.
Follow this link to view a map of New Mexico Rivers.
The Middle Rio Grande Valley includes four New Mexico counties and six Indian pueblos. Other principal land and facility managers include the Middle Rio Grande Conservancy District, Bureau of Reclamation, Army Corps of Engineers, New Mexico Department of Game and Fish, U.S. Fish and Wildlife Service, New Mexico State Parks, the City of Albuquerque Parks and Recreation Division, and private landowners.
Follow this link to view a map of the Middle Rio Grande Valley.
The dominant geographic feature in the Middle Rio Grande Valley is the Rio Grande Rift, which extends more than 500 miles (800 km) from central Colorado through New Mexico. A rift occurs when two sides of a fault zone pull away from each other, leaving a large, trench-like valley. The crust beneath the rift has been stretched and thinned by extensional fault movements. The valley is actually a series of basins, each slightly lower in elevation as you move south (thus to call it a single rift is not quite correct, as that implies a single trough, but it is typically referred to this way). Each of these basins once contained its own ephemeral (seasonal) lake. Over time water eroded the canyons between basins, eventually merging into the continuous river. The term "valley" is thus also not technically correct, because a valley is carved by a river that cuts through the bedrock rather than taking advantage of a trough that was already there, but this is another term that is accepted as correct and so will be used here. The Rio Grande Rift has been geologically active for about the last 20 million years while the Rio Grande itself has flowed in its current location through the valley 1-2 million years.
The climate of the region has been arid to semi-arid over the past 5,000 years, although cyclical drought/wet-year patterns have occurred during this period. These cycles are influenced by the El Nino/La Nina phenomenon, which is caused by periods of variation in water temperatures and barometric pressures in the eastern Pacific Ocean. During El Nino years, New Mexico experiences higher than average winter precipitation, resulting in high spring flows in the Rio Grande, as well as in the Pecos and Gila rivers. In contrast, La Nina years result in drought conditions here in the valley and low water levels in the river.