The Dolores River rises in a meadow called Tin Can Basin, near Hermosa Peak in the San Miguel Mountains, in Dolores County, Colorado. The headwaters are located about south of Lizard Head Pass in the San Juan National Forest. The river flows southwest in a canyon past Rico, receiving the West Dolores River, then flows into McPhee Reservoir near Dolores in Montezuma County. Formed by McPhee Dam, the reservoir is about long and diverts flows of the upper Dolores River for irrigation.