San Luis Valley is a large broad alpine valley in south-central Colorado. The valley 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 long and about 74 miles wide extending from the Continental Divide on the northwest to the New Mexico state line on the south. Parts of New Mexico are also considered to be part of the San Luis Valley.

The Sangre de Christo Range (sometimes called locally the East Range) is the eastern border of the valley. Mt. Blanca is prominent in the middle of the range. There are several passes at between 9 and 10 thousand feet, La Veta pass being used by US Highway 160 and by the Denver and Rio Grande Railroad (D. & R. G.) tracks. Other passes used historically were Medano, Mosca and Sangre de Christo Passes.

Elevation rises as you go north in the valley to Poncha Pass, used now by US Hiway 285 and historically by the narrow gauge tracks of the D. & R. G.

About 50% of the 2 million acres in the San Luis Valley is privately owned.

500,000 acres on the borders of the valley, generally abutting National Forest Lands are managed by the Bureau of Land Management, BLM, a division of the United States Department of the Interior. This land is usually leased to neighboring ranches for grazing for a nominal fee. Part of the value of a ranch is its continuing lease of BLM or National Forest lands.

Public lands in the mountains surrounding the San Luis Valley are generally part of the Rio Grande National Forest and are managed by the United States Forest Service.