Aquifers and Artesian Wells
Artisian wells are free-flowing streams under pressure that spout out of the groud. Alamosa’s first town water supply was from artesian wells. Since the 1970s artesian wells must be capped and no new ones can be milled, so as to preserve the underground aquifer.
When the mountain streams sink into the porous floor of the San Luis Valley, seepage does not continue downward unimpeded. Rather, it is impounded by a relatively impermeable layer of clay that divides the upper unconfined aquifer from the lower confined aquifer. The unconfined aquifer sits on top of this impermeable layer and essentially forms the water table, which resides within the sandy alluvium and gravel subsurface of the Alamosa Basin. The depth of the confining clay layer varies from about 100 feet in the northern part of the Rio Grande Basin to about 40 feet in the southern part. There is nothing between it and the surface of the valley floor to prevent it from appearing as surface water in lowlying areas, such as within lakes and creek beds. Shallow unconfined groundwater occurs almost everywhere in the valley and extends 50 to 200 feet beneath the land surface. The depth to water in about 50 percent of the valley is less than 12 feet.