Some notes on the hydrogeology and ground-water quality of the Animas Basin system, southwestern New Mexico
— Barry J. Hibbs, Monica M. Lee, John W. Hawley, and John F. Kennedy

The Animas basin system comprises an interconnected group of four subbasins (Lordsburg, Lower and Upper Animas, and Cloverdale) with a total surface watershed of about 6340 km², and a ground-water flow system area of about 6025 km² . Very small portions of the system, 35 km² and 90 km² , respectively, extend into Arizona and Mexico. The remaining 6215 km² is located in southwestern New Mexico, including parts of Hidalgo, Grant, and Luna counties. Water-bearing strata include consolidated bedrock units in the flanking highlands, and Tertiary and Quaternary basin (bolson) fill units in the central portions of the basin system. Recharge occurs mostly from ephemeral recharge along mountain fronts and from infiltration beneath the stream channel and floodplain of the system's only major axial drainageway, Animas Creek, Ground water flows south–north from the Cloverdale and Upper Animas subbasins, through the Lower Animas subbasin, into the Gila River Valley. Ground water along the regional hydraulic gradient is also captured by irrigation pumping. A smaller component of discharge is by evaporation where depth to groundwater is less than 10 to 12 m. Interior surface drainage collects at Alkali Flats and ground water discharges partly (and almost entirely under pre development conditions) by subsurface interbasin flow; thus the basin system is classified as a topographically closed and drained basin. Hydrochemical facies in the basin system developed as a result of water-rock and water-soil interactions along flowpaths. Hydrochemical facies vary from calcium-bicarbonate ground waters with total dissolved solids (TDS) less than 250 mg/L in the Cloverdale and Upper Animas subbasins, to sodium bicarbonate groundwaters with TDS less than 1000 mg/L in the southern part of the Lower Animas subbasin, to sodium sulfate and sodium-chloride-sulfate ground waters with TDS that sometimes exceeds 1000 mg/L near Alkali Flats in the northern part of the Lower Animas subbasin. Different hydrochemical facies and higher TDS developed as ground water flowed south–north. The primary processes responsible for hydrochemical evolution and salinization include gypsum and halite dissolution, exchange on clay particles of bound sodium for calcium and magnesium in solution, and evaporation where ground water is shallow.