San Luis Closed Basin

While the basin is east of the majority of the Rocky Mountains, it lies west of the Sangre de Cristo Range.

[1] 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, of which the endpoint was a playa adjacent to the Great Sand Dunes.

The hydrology[clarification needed] of the Closed Basin is currently monitored and managed by the Rio Grande Water Conservation District.

It forms part of the breeding area of the southwestern willow flycatcher, a bird that is a United States endangered subspecies.