The river rises high in Colorado's
South San Juan Wilderness near the
Continental Divide in
Conejos County, Colorado. From there, it flows generally southeast until it is impounded by the dam at
Trujillo Meadows Reservoir. Leaving the reservoir, the river passes under
Colorado State Highway 17 and turns south. Here, it receives a tributary, North Fork Rio de los Pinos. Continuing south, the river has its confluence with Cumbres Creek. Here, the river flows generally east until it passes by
Osier, Colorado. There, the river turns south and enters
Rio Arriba County, New Mexico. Next it passes through the Toltec Gorge. Then the river flows generally east and southeast through New Mexico until it reaches the
Rio Grande del Norte National Monument. At this point, it turns northeast, crosses the border into Colorado once again, still in Conejos County, and joins the Rio San Antonio. ==Public lands==