Geohydrology of the aquifer in the Santa Fe Group, northern West Mesa of the Mesilla Basin near Las Cruces, New Mexico

Abstract

The West Mesa of the Mesilla Basin in south-central New Mexico encompasses an undeveloped area of approximately 750 square miles west of the Rio Grande. In order to provide for orderly development of the ground^water supplies in the northern West Mesa, information is needed about the geohydrologic characteristics of the aquifer in the Santa Fe Group. The Santa Fe Group consists of Quaternary and Tertiary piedmont-slope, fluvial, playa, and lacustrine deposits composed of clay, silt, sand, gravel, and caliche, and igneous rocks composed of volcanic ash and basalt. The saturated thickness of the aquifer in the Santa Fe Group ranges from about 3,440 feet at the Boles No. 1 Federal oil test well to zero at. the western and northern borders of the study area. Because of the heterogeneity of the Santa Fe Group, the hydrologic characteristics of the aquifer vary substantially from place to place. Hydraulic conductivities of 12 and 30 feet per day were estimated from aquifer tests for two wells in the eastern onehalf of the study area. Some of the well yields in the eastern one-half of the study area are greater than 1,000 gallons per minute. Well yields in the western one-half of the study area generally are less than 5 gallons per minute. Across the eastern one-half of the study area, ground water flows southeastward at a gradient of less than 5 feet per mile. Group water flows southeastward across the western one-half of the study area at a gradient of about 50 feet per mile. Dissolved-solids concentrations in ground water range from 378 to 556 milligrams per liter in the eastern one-half of the study area and from 906 to 1,470 milligrams per liter in the western one-half.