The San Luis Closed Basin is a

endorheic An endorheic basin ( ; also endoreic basin and endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water (e.g. rivers and oceans); instead, the water drainage flows into permanent ...

basin in the Alamosa and Saguache counties of south-central

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

. It includes San Luis Creek and its tributary, Saguache Creek. While the basin is east of the majority of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

, it lies west of the Sangre de Cristo Range. An elevated plateau in Alamosa County, the

San Luis Hills The San Luis Hills are a group of small mountain ranges in Conejos County, Colorado, Conejos and Costilla County, Colorado, Costilla counties in the San Luis Valley in southern Colorado. The individual mountain ranges that make up the San Luis Hil ...

, separates the San Luis Closed Basin drainage from most of the

San Luis Valley The San Luis Valley is a region in south-central Colorado with a small portion overlapping into New Mexico. The valley is approximately long and wide, making it the largest alpine valley in the world. It extends from the Continental Divide on ...

, which is southward-flowing and drains through the

Rio Grande The Rio Grande ( or ) in the United States or the Río Bravo (del Norte) in Mexico (), also known as Tó Ba'áadi in Navajo language, Navajo, is one of the principal rivers (along with the Colorado River) in the Southwestern United States a ...

Hydrology

The San Luis Closed Basin forms a major segment of the eastern slope of the Colorado section of the

Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...

. Historically, all of the waters that naturally entered the basin through hydrologic processes were disposed of by

evapotranspiration Evapotranspiration (ET) refers to the combined processes which move water from the Earth's surface (open water and ice surfaces, bare soil and vegetation) into the Atmosphere of Earth, atmosphere. It covers both water evaporation (movement of w ...

, of which the endpoint was a playa adjacent to the Great Sand Dunes. Starting in the 1970s, part of the water that had previously flowed toward the playa was diverted to the Rio Grande drainage through a canal constructed in the 1970s as part of the Closed Basin Project. As part of the Project, part of the former playa was redeveloped as an intermittent recreational lake, San Luis Lake. Some of the water from the Basin continues to be allocated to San Luis Lake for recreational purposes. The hydrology of the Closed Basin is currently monitored and managed by the Rio Grande Water Conservation District.

Ecology

The San Luis Closed Basin is disturbed semiarid land characterized by widespread patches of greasewood, often locally called "chico" or "chico brush." It forms part of the breeding area of the southwestern willow flycatcher, a bird that is a United States endangered subspecies.

References

{{reflist Landforms of Alamosa County, Colorado Landforms of Saguache County, Colorado Rio Grande San Luis Valley of Colorado Endorheic basins of the United States