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<br />Location of the study area (the lower Gunnison River basin) and location <br />of previous aquifer studies on the Western Slope of Colorado are shown in the <br />index map (fig. 1). Most data in this report were collected during 1980 and <br />1981. The system of numberin'g data sites, local identifier in tables 3, 4, <br />and 5, is explained in figure 2. <br /> <br />Approach <br /> <br />Data for this report were compiled from discussions with well and spring <br />users and from drillers' records of water wells, from completion reports and <br />logs for oil and gas test wells, from geologic maps, and from chemical analy- <br />ses of water samples from wells and springs. The data reported here consist <br />of: (1) Verified hydrogeologic data from 51 wells and 61 springs, (2) geo- <br />logic and hydrologic data from 71 additional wells based on drillers' reports, <br />and (3) chemical analyses of water samples from 34 wells and 17 springs. <br /> <br />Data collected include measured water level, depth of well, discharge of <br />well or spring, water-quality information, type of water use, well or spring <br />location, geology, and other hydrogeologic information. All data-collection <br />sites for inventoried and noninventoried wells are shown in plate 1. <br /> <br />Data reported for sites visited as a part of this study are shown in <br />tables 3, 4, and 5 in the "Supplemental Information" section at the end of <br />this report. Data in table 6, also in the "Supplemental Information" section, <br />are from, or are derived from, well reports provided by the State Engineer's <br />Office. Data in tables 3, 4, 5, and 6 may not represent conditions through- <br />out the aquifer because of the discontinuous nature of aquifers and irregu- <br />larity of water chemistry in some aquifers and irregular distribution of <br />fracturing and zones of saturation. Many of these wells were not completed <br />for optimum yield or penetrate only part of the aquifer. Wells penetrating <br />the full aquifer thickness, and which have well screens in all sand or sand- <br />stone zones in the aquifer, might have greater yields than most of those <br />listed in table 6. Some reported yields were from very short tests; there- <br />fore, some wells might not support the reported yield for a longer period of <br />time than the test. Well yields given in this report are based on reported <br />well yields given by drillers' records on file with the Colorado State Engi- <br />neer's Office. <br /> <br />Previous Investigations <br /> <br />General hydrology of the study area was reported by Iorns and others <br />(1965). Hydrogeologic maps in this report were prepared from geologic maps by <br />Cashion (1973), Tweto, Moench, and Reed (1976), Tweto and others (1976) and <br />Williams (1964). Lee (1912) described the geology in western Delta County. <br /> <br />Acknowledgments <br /> <br />Data collected for this report are the result of cooperation from basin <br />residents who provided information on wells and springs, permitted measure- <br />ments to be made, and allowed water-quality sampling. The Colorado State <br />Engineer's Office assisted with the well and spring inventory and provided <br />well records. <br /> <br />2 <br />