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<br />, <br /> <br />the Picacho Drain on the west. The Del Rio, the East, and the Montoya Intercepting Drains <br />discharge into the river from the east below the Mesilla Diversion Dam. The Santo Tomas <br />River, La Mesa, and the West Drain discharge into the river from the west below the Mesilla <br />Diversion Dam. The Nemexas and the West Drains are additional major drains of the west side <br />of the river that discharge into the Montoya Intercepting Drain through the Montoya Drain <br />Siphon. <br /> <br />Both the flood-plain alluvium and the basin-fill deposits in the Santa Fe Group are <br />significant aquifers in the Mesilla Valley and have been developed for irrigation, municipal, and <br />industrial purposes. The flood-plain alluvium is reported to be 60 to 80 feet thick, consisting of a <br />basal layer of gravel 30 to 40 feet thick overlain by lenses of sand, gravel, and clays. The <br />deposits of the Santa Fe Group are reported to be predominantly sand with layers of gravel, silt, <br />clay and sandy clay. These deposits are more than 2,000 feet deep in some parts of the valley, <br />but their thickness varies considerably. Typically, the deposits are thicker in the central part of <br />the valley than in the northern part. Recharge to these aquifers occurs from precipitation, <br />irrigation, and seepage from canals and the Rio Grande and its tributaries. Ground water in the <br />basin-fill in the Santa Fe Group may be confined in some areas under the valley-fill alluvium. <br /> <br />The deposits of the Santa Fe Group in the Lower Mesilla Valley have been separated by <br />recent investigators into three aquifers based on differences in lithology, water levels, and water <br />quality. Wells in the shallow aquifer extend to a depth of 200 feet or less; wells in the medium <br />aquifer are screened ranging from 168 to 550 feet, and wells in the deep aquifer are screened at <br />depths ranging from 512 to 1,200 feet (White, 1987). Water quality is reportedly better in the <br />deeper aquifers. The southern end of the valley is a bedrock covered with a thin alluvial veneer. <br />Lillie ground water leaves the Mesilla Valley (Wilson and others, 1981). <br /> <br />r'-- C :', <br />..)...., \) '-' <br />We have not been able to obtain complete data on the development of irrigation wells in <br />the Mesilla Valley, but it has been significant. Some of the data that are available relate to both <br />the Rincon and Mesilla Valleys. Anderholm (1992, p. e7) summarized some of the data that are <br />available of the development of these wells. In February 1948, about 70 wells had been <br />constructed in the Rincon and Mesilla Valleys. Several hundred irrigation wells were <br />constructed in the 1950$ as the result of shortages in the surface water supply. White (1981, p. <br /> <br />2 -12 <br /> <br />\. . "~i(;#t~l,,',y' <br />