The San Miguel River is a tributary of the Dolores River

Dolores River

The Dolores River is a tributary of the Colorado River, approximately 250 mi long, in the U.S. states of Colorado and Utah....

, approximately 90 mi (145 km) long in southwestern Colorado

Colorado

Colorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...

 in the United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. It rises in the San Juan Mountains

San Juan Mountains

The San Juan Mountains are a high and rugged mountain range in the Rocky Mountains in southwestern Colorado. The area is highly mineralized and figured in the gold and silver mining industry of early Colorado. Major towns, all old mining camps, include Creede, Lake City, Silverton, Ouray, and...

 southeast of Telluride

Telluride, Colorado

The town of Telluride is the county seat and most populous town of San Miguel County in the southwestern portion of the U.S. state of Colorado. The town is a former silver mining camp on the San Miguel River in the western San Juan Mountains...

 and flows northwest, along the southern slope of the Uncompahgre Plateau

Uncompahgre Plateau

The Uncompahgre Plateau in western Colorado is a distinctive large uplift part of the Colorado Plateau. Uncompahgre is a Ute Indian word that describes the water: "Dirty Water" or "Rocks that make Water Red"....

, past the towns of Placerville

Placerville, Colorado

Placerville is an unincorporated town and a U.S. Post Office located in San Miguel County, Colorado, United States. The Placerville Post Office has the ZIP Code 81430.-History:...

 and Nucla

Nucla, Colorado

Nucla is a Statutory Town in Montrose County, Colorado, United States. The population was 734 at the 2000 census. Its name comes from the town's founders intent that it serve as a "nucleus" for the surrounding farms and mines, although it has since come to be associated with the growth of uranium...

 and joins the Dolores in western Montrose County

Montrose County, Colorado

Montrose County is the 17th most populous of the 64 counties of the State of Colorado of the United States. The county population was 41,276 at U.S. Census 2010. The county was named for its county seat, the City of Montrose...

 approximately 15 miles (24 km) east of the state line with Utah

Utah

Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...

.

The San Miguel is more or less free flowing; however, diversion dams dot the river and alter flows. The San Miguel varies in gradient, from extremely steep in its upper reaches (forming a shallow, rocky, unnavigable stream) to more mellow in the lower sections (30 ft/mi of drop, which offers the whitewater boater a variety of runs all within the class II+--III range). All told, the San Miguel drops over 7000 feet (2,133.6 m) from an alpine ecosystem to the desert. The average flow is about 600 cuft/s.