New Mexico Geological Society Annual Spring Meeting — Abstracts

The San Agustin Basin, Alamosa Creek basin upstream from I Monticello Box, and the upper Gila Basin are located in parts of Catron, Socorro, and Sierra Counties in west-central New Mexico. There are four major aquifers within the study area: the San Agustin bolson-fill aquifer; the Alamosa Creek shallow aquifer; and the Datil and the shallow upland aquifers, which are present in all basins. Three minor aquifers, the Baca Formation at the northern edge of the San Agustin Basin, a basalt to basaltic andesite unit overlying the Datil Group in the San Agustin and Gila basins, and the Gila Conglomerate in all basins, produce some water. Potentiometric-surface maps were constructed to determine the hydraulic gradients of the San Agustin bolson-fill aquifer, the Datil aquifer, and the Alamosa Creek shallow aquifer. Dissolved-solids concentrations of water samples from all aquifers rangedfrom 74 to 23,500 milligrams per liter. The dominant cations varied; the dominant anion of freshwater generally was bicarbonate. Vertical electrical-resistivity sound ings were used to estimate the thickness of bolson-fill and the depth of the saline-water/freshwater interface in the San Agustin bolson-fill aquifer. Pointof-discharge temperatures of well or spring water that are greater than 21° Celsius are associated with faults in the areas of shallow or exposed bedrock. The dissolved solids concentration of warm water ranged from 120 to 1,200 milligrams per liter.