Groundwater
In the San Luis Valley, runoff from the San Juan and Sangre de Cristo Mountains sinks into layers of sand in the Alamosa Formation. Flowing along the sand layers toward the center of the valley, it provides [artesian water] for irrigation of valley farmlands.
SAN JUAN MOUNTAINS LIMIT OF FLOWING WELLS HUBBARD’S WELL OTTOWAY’S WELL ALAMOSA WELL GEORGE NEWSOM’S WELL CALKIN’S WELL LIMIT OF FLOWING WELLS [Moraine] Alluvial Slope SANGRE DE CRISTO MOUNTAINS Sands, [lava] beds, gravels, [conglomerates], etc. Alamosa formation [Granites] WEST SANTE FE FORMATION SANTE FE FORMATION EAST
Groundwater is extremely important to Colorado, especially in the Prairie Province and the San Luis Valley. Below these two areas lie a number of distinct and productive groundwater [aquifers], several of them artesian. In Otero County, for example, there are five major aquifers: three separate Quaternary gravel deposits, the Cretaceous Dakota Sandstone, and the Cheyenne Sandstone Member of the Purgatoire Formation, also Cretaceous. All these aquifers are characterized by their high porosity and permeability, which allow water to flow rapidly through them. Wells in the younger, shallower aquifers produce as much as 2,000 gallons per minute; those in the older, deeper aquifers produce about eighty gallons per minute, some of it with an artesian “head.”
The San Luis Valley supports intensive agriculture, made possible by a great [artesian water] supply. A thick series of soft interlayered clays and sands, the Alamosa Formation, slopes down toward the center of the basin from the surrounding mountains. Water entering the sandstone beds at the mountain edges flows through the sand layers held there by the impermeable clay beds. By the time it reaches the center of the valley, it has developed considerable hydrostatic head, and the water rises in wells without pumping. Unfortunately, both the irrigation water and the soils in the San Luis Valley are highly alkaline. Constant evaporation from the irrigated fields has concentrated the alkali near and on the surface, rendering some of the land less usable than it was originally.