Dolores/San Juan/San Miguel Basin

The Dolores/San Juan/San Miguel Basin, also referred to as the Southwest Basin, encompasses nine distinct sub-basins, all of which flow out of state before they reach the San Juan River in New Mexico or the Colorado River in Utah. Its major rivers are the San Juan, the Dolores and the San Miguel. The basin covers an area of about 10,170 square miles. Within it, the largest cities are Durango (population 18,500) and Cortez (population 9,000).

Number of “sub-basins” in southwestern Colorado’s Dolores/San Juan/San Miguel Basin

Most Southwest Basin headwaters originate on federal land owned by the U.S. Forest Service and the Bureau of Land Management. Federal agencies have worked with the Colorado Water Conservation Board’s Instream Flow Program to secure flow protection at high elevations throughout the basin. Many lower elevation lands are privately owned and used to raise cattle and grow crops like alfalfa, corn, wheat, hay and pinto beans. Recreation is also a major economic driver in the basin, with tourists drawn from all over the country for rafting, skiing, fishing and mountain biking.

Waters from the southwestern part of the state are shared with neighboring states and tribes. The 1922 La Plata River Compact divides waters between Colorado and New Mexico, while the 1968 Animas-La Plata Project Compact recognizes that New Mexico has a right to divert and store water in Colorado for uses in New Mexico under the Animas-La Plata Federal Reclamation Project. 

Today, the Animas-La Plata Project primarily provides water to the Ute Mountain Ute and the Southern Ute tribes and to local and state agencies in Colorado, but it also provides water to the Navajo Nation and the La Plata Water Conservancy District in New Mexico. The San Juan-Chama Project, authorized in 1962, also moves water from the Southwest Basin’s Rio Blanco to the Rio Grande Basin in New Mexico.

The basin is home to the Southern Ute Indian Tribe and the Ute Mountain Ute Indian Tribe, the only two reservations in Colorado. The Colorado Ute Indian Water Rights settlement of 1988 allocated water for these tribes through the Dolores Project, where Dolores River water is stored in McPhee Reservoir, and the Animas-La Plata Project, where Animas River water is stored in Nighthorse Reservoir. 

The Animas-La Plata Project provided the tribes with a municipal and industrial water source to supply and augment future depletions of the San Juan River system that are constrained by the San Juan Basin Recovery Implementation Program for endangered native fish. It also provided the City of Durango and nearby areas with municipal and industrial water.

Some environmental challenges endure in the basin, such as coping with a legacy of abandoned hard rock mines that continue to impact water quality. This problem was brought into high relief in 2015, when U.S. Environmental Protection Agency workers mitigating pollution at the Gold King Mine near Silverton accidentally caused the release of 3 million gallons of water laced with metals into the Animas River. The spill affected municipal and agricultural water supplies as far away as Farmington, New Mexico, and Utah.

Water users from across southwestern Colorado convene through the Southwest Basin Roundtable to discuss and find consensus on such challenges, approve funding, and work on water planning.

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