Great Sand Dunes National Park and Preserve and Sangre de Cristo Mountains from San Luis Valley, Colorado
The San Luis Valley is an extensive high-altitude depositional basin in the U.S. state of Colorado with a small portion overlapping into New Mexico covering approximately 8,000 square miles (21,000 km2) and sitting at an average elevation of 7,664 feet (2,336 m) above sea level. The valley is a section of the Rio Grande Rift and is drained to the south by the Rio Grande, which rises in the San Juan Mountains to the west of the valley and flows south into New Mexico. The valley is approximately 122 miles (196 km) long and 74 miles (119 km) wide, extending from the Continental Divide on the northwest rim into New Mexico on the south. The San Luis Valley receives little precipitation and is made up of desert lands, but the temperatures can be very comfortable in the summer and very cold on winter nights.
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.