5.9 - DOLORES RIVER BASIN
The Dolores and San Miguel Rivers originate in the Rico, La Plata, and San Juan Mountains of southwest Colorado. The Dolores River basin is about 95 miles long from northwest to southeast and encompasses an area of just over 5,300 square miles, including parts of Montezuma, Dolores, San Miguel, Montrose, and Mesa counties. The San Miguel River basin is tributary to the Dolores River, is 68 miles long, and encompasses about 1,600 square miles, including portions San Miguel and Montrose counties. The Dolores River basin falls within both Water Management Divisions 4 and 7. Less than 100 alluvial wells have been recorded with the State Engineer’s Office. The occurrence and distribution of alluvium along the Dolores and San Miguel Rivers is shown in yellow on Figure 5.9-1.
Both river basins overlie substantial portions of the Paradox Basin. Altitudes in the Dolores and San Miguel River basins range from about 14,200 feet near the Dolores River headwaters to 4,100 feet at their combined confluence with the Colorado River in Utah. Alluvial aquifers in the Dolores River basin are very limited in extent and are restricted to areas immediately adjacent to the main river channels. Within Division 7, most of the mapped alluvial deposits are located at, or upstream of, the town of Dolores. In Division 4, mapped alluvial deposits are localized around Gateway and in West Creek.
Although restricted in extent, the alluvium is an important aquifer to those people who utilize it for domestic, stock, and minor irrigation use. Population is sparse in the Dolores and San Miguel River basins, with the 2000 Census indicating that approximately 65,700 people live in the combined Dolores, San Miguel, Montezuma, and Montrose Counties.