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Show PART V GROUND WATER General Availability of Ground Water The general availability of ground water to individual wells is shown on the map on the following page. This map is based in part on records of wells and in part on the geology. Yields to individual wells generally range from 5 to 50 g.p.m. (gallons per minute) over a major portion of the region. Yields of 50-500 g.p.m. can be expected from wells that tap alluvium along some of the major streams. Most wells along these streams for which records are available have yields nearer the lower limit. In a few local areas, such as the Fremont River Valley and Spanish Valley in southeastern Utah, yields as high as 500 g.p.m. are generally avail- able, and yields of more than 1,000 g.p.m. are possible from properly constructed large-diameter wells. Wells in the upper Fremont River Valley tap aquifers in both the alluvium and igneous rocks. Numerous springs and seeps are scattered throughout the region. They most commonly discharge along faults, geologic contacts, or where stream channels intersect the water table. Most of the individual springs and seeps yield a few g.p.m., some yield more than 100 g.p.m., but only a very few widely scattered springs yield more than 450 g.p.m. The largest springs generally occur near the headwater areas of the larger streams. Depths to Ground Water Levels The depth to ground water is a factor affecting general availability and particularly the cost and feasibility of pumping. The following map shows the general depths to water levels. In general, depths to ground water levels are shallowest, generally less than 100 feet below land surface, in much of the Wyoming portion and along the alluvial plains of the main streams that are tributary to the Colorado River in other parts. Levels are deepest, generally more than 500 and locally more than 1,000 feet below land surface, in the Colorado Plateau adjacent to the deeply incised Colorado and San Juan Rivers. Data in the mountainous areas and high plateaus are inadequate to determine depths to water. Depths to water levels in these areas probably range from only a few feet below land surface along most stream channels to more than 500 feet below land surface near the divides between streams. Unconfined or artesian conditions in the water-bearing rocks in some subregions cause depths to ground water levels to vary from several hundred feet below land surface to several tens of feet above land surface at the same locality. For example, in parts of the San 19 |