Significant quantities of fresh ground water occur in the basin fill of the northern Hueco bolson and lower Mesilla Valley and in the Wildhorse Flat, Michigan Flat, Lobo Flat, and Ryan Flat areas of the Salt Basin; and may occur in Red Light Draw, Presidio bolson, and Green River valley. More than 20 million acre-feet of freshwater is estimated to be in storage in the basin fill of westernmost Texas. About 12 million acre-feet, or more than half, is in El Paso County in the Hueco bolson and Mesilla Valley. In addition, the basins contain about 7 million acre-feet of slightly saline water in basin fill, in Rio Grande alluvium in the Hueco bolson and lower Mesilla Valley, and in the Capitan Limestone in the northern Salt Basin. Ground-water pumping for municipal supply and industrial use in the El Paso area caused water-level declines of as much as 74 feet during 1903-73, and pumping for irrigation in the Salt Basin caused a maximum decline of 150 feet at Lobo Flat during 1949-73. Additional development of ground water in westernmost Texas will be accompanied by further declines in water levels, and will probably induce local migration of slightly saline or poorer quality water into freshwater areas. Land-surface subsidence could occur in local areas where water-level declines are large and the basin fill contains large amounts of compressible clay. (Kosco-USGS)
