San Luis Valley - Geography

Geography

The San Luis Valley is the broad, generally flat, valley at the headwaters of the Rio Grande in south central Colorado and far north central New Mexico. The northern portion of the San Luis Valley is an endorheic basin, which is to say that surface water does not exit this area. The southern portion is drained by the Rio Grande.

There is no clear southern boundary but the term is generally used to include the San Luis Hills of southern Colorado and the Taos Plateau of northern New Mexico. About 50 miles from east to west and about 150 miles from north to south, the valley is bounded on the east by the Sangre de Cristo Mountains and on the west by the San Juan Mountains.

Within Colorado the San Luis Valley is generally considered to comprise six Colorado counties: Saguache, Alamosa, Rio Grande, Conejos, Costilla and Mineral. The principal towns are: Alamosa, Monte Vista, Del Norte, South Fork, Creede, Saguache, Center, Fort Garland, San Luis, Antonito, La Jara, Capulin, Manassa, Sanford, Crestone, Villa Grove, Hooper, Mosca, San Acacio and a number of smaller locations. A few other counties of Colorado have some land in the Rio Grande Basin including Archuleta County, Hinsdale County and San Juan County.

Blanca Peak is prominent in the Sierra Blanca at the southern end of the northernmost section of the mountains, which is known as the Sangre de Cristo Range. There are several passes, with elevations between 9,000 and 10,000 feet (2,700 and 3,000 m), giving access to the valley. North La Veta Pass, through the Sangre de Cristo Mountains, is used by US Highway 160 and by the San Luis and Rio Grande Railroad (formerly a branch of the Denver & Rio Grande Western) tracks. Other passes used historically were Medano, Mosca and Sangre de Cristo Passes.

The Great Sand Dunes is a famous feature of the valley. It lies directly to the west of the Sangre de Cristo Mountains. The dunes can reach 750 feet (230 m) high. The Great Sands Dunes National Park and Preserve is now in place to protect both the dunes and the numerous archeological sites found in the area. The natural valley aquifer is close to the surface in this part of the valley, and helps with maintenance of water levels in the San Luis Lakes, just to the west of the sand dunes.

Elevation rises as you go north in the valley to Poncha Pass, used now by US Highway 285 and historically by the narrow gauge tracks of the Denver and Rio Grande Railroad. Otto Mears, then of Saguache, built and operated an historic toll road over Poncha Pass at the north end of the valley into the San Luis Valley during Colorado's 19th century mining era when the valley was the gateway to the San Juan and Gunnison country and the Ute agency was in the mountains west of Saguache.

Cumbres Pass is a 10,015 ft. pass between Antonito, Colorado and Chama, New Mexico. The pass is traversed by State Highway 17 and the Cumbres and Toltec Scenic Railroad (originally built as the San Juan Extension of the Denver and Rio Grande Railroad that ran to Durango, Colorado). From the headwaters of the Rio Grande Wolf Creek Pass is the route of U.S. Highway 160 between Del Norte, Colorado and Pagosa Springs, Colorado, while Slumgullion Pass is the route of State Highway 149 between U.S. Highway 160 and Lake City, Colorado. Stony Pass, sometimes spelled Stoney Pass, an historic wagon road to the mining camps of the San Juans, is now a jeep trail. At the north end of the valley, North Pass is the route of State Highway 114 between Saguache, Colorado and Gunnison, Colorado, bypassing the original route over Cochetopa Pass, now a county road.

The Rio Grande follows a course through the southern valley from Del Norte southeastward via Alamosa to New Mexico. South of Alamosa it is joined by several streams from the west including the Alamosa River and the Conejos River and Culebra Creek from the east. Most of the northern valley is an endorheic basin called the Closed Basin. Generally, within the Closed Basin the major streams such as Saguache Creek, San Luis Creek, and the streams from the west face of the Sangre de Cristos flow only a short distance onto the valley floor as surface streams. Only in very wet years, perhaps every 20 years, does the stream system in the Closed Basin flow as a connected unit into San Luis Lake at the low point of the Closed Basin west of the Great Sand Dunes.