The San Luis Closed Basin is a

endorheic An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes ...

basin in the

Alamosa Alamosa is a home rule municipality and the county seat of Alamosa County, Colorado, United States. The city population was 9,806 at the 2020 United States Census. The city is the commercial center of the San Luis Valley in south-central Colora ...

and Saguache counties of south-central

Colorado Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...

. It includes San Luis Creek and its tributary,

Saguache Creek Saguache Creek The place name "Saguache" is pronounced . This name derives from the Ute language noun "''sawup''" meaning "sand dunes". The Spanish language version of this name is usually spelled "Saguache", while the English language version ...

. 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 straight-line distance from the northernmost part of western Canada, to New Mexico ...

, it lies west of the

Sangre de Cristo Range , country= United States , subdivision1= Colorado , subdivision2_type= Counties , subdivision2= , parent= Sangre de Cristo Mountains, Rocky Mountains , borders_on= , geology= , age= , orogeny= Fault-block mountains , area_mi2= ...

. An elevated plateau in Alamosa County, the San Luis Hills, separates the San Luis Closed Basin drainage from most of the San Luis Valley, which is southward-flowing and drains through the Rio Grande.

Hydrology

The San Luis Closed Basin forms a major segment of the eastern slope of the Colorado section of the Continental Divide. Historically, all of the waters that naturally entered the basin through hydrologic processes were disposed of by

evapotranspiration Evapotranspiration (ET) is the combined processes by which water moves from the earth’s surface into the atmosphere. It covers both water evaporation (movement of water to the air directly from soil, canopies, and water bodies) and transpi ...

, 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 The Closed Basin Project is a groundwater extraction project in the San Luis Valley in Colorado, United States, that began in the 1970s, and remains in operation in the 2020s. The project is managed by the United States Bureau of Reclamation. L ...

. 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 Greasewood is a common name shared by several plants: * ''Adenostoma fasciculatum'' is a plant with white flowers that is native to Oregon, Nevada, California, and northern Baja California. This shrub is one of the most widespread plants of the ...

, often locally called "chico" or "chico brush." It forms part of the breeding area of the

southwestern willow flycatcher The willow flycatcher (''Empidonax traillii'') is a small insect-eating, neotropical migrant bird of the tyrant flycatcher family. There are four subspecies of the willow flycatcher currently recognized, all of which breed in North America (inc ...

, a bird that is a United States

endangered subspecies An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and inv ...

References

{{reflist Landforms of Alamosa County, Colorado Landforms of Saguache County, Colorado Rio Grande San Luis Valley of Colorado