The San Agustin Basin, the Alamosa Creek Basin upstream from Monticello Box, and the upper Gila Basin are located in parts of Catron, Socorro, and Sierra Counties in west-central New Mexico. Four major aquifers are within the study area: (1) the San Agustin bolson-fill aquifer; (2) the Datil aquifer; (3) the shallow upland aquifers; and (4) the Alamosa Creek shallow aquifer. Two minor aquifers, the Baca Formation at the northern edge of the San Agustin Basin and a basalt to basaltic andesite unit overlying the Datil Group, yield some water to wells. Sixty-three vertical electrical- resistivity soundings were used to estimate the depth to bedrock and the saline/freshwater interface in the San Agustin bolson-fill aquifer. The dissolved-solids concentration of ground-water samples ranged from 74 to 23,500 milligrams per liter. The dominant cations varied; the dominant anion of freshwater generally was bicarbonate. Point-of-discharge temperatures of well or spring water that exceed 21 degrees Celsius are associated with faults in the areas of shallow or exposed bedrock. The dissolved-solids concentration of this warm water ranged from 120 to 1,200 milligrams per liter.
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USGS Numbered Series
Geohydrology of the San Agustin Basin, Alamosa Creek Basin upstream from Monticello Box, and upper Gila Basin in parts of Catron, Socorro, and Sierra counties, New Mexico