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The basal portion of the Laramie Formation contains two relatively thick sandstone units <br />(the A and B sandstones) which are hydraulically isolated from the upper part of the formation. <br />These sandstone units, combined with the underlying Fox Hills Sandstone, compose the <br />hydrogeologic unit of the Laramie -Fox Hills aquifer. <br />LARAMIE-FOX HILLS AQUIFER <br />The lowermost of the four Denver Basin aquifers is the Laramie -Fox Hills aquifer which <br />underlies approximately 6,700 square miles and marks the areal extent of the basin for economic <br />ground water development. The Laramie -Fox Hills aquifer is generally between 250 and 300 <br />feet thick, and includes about 150 to 200 feet of fine-grained and medium -grained sandstone. <br />The aquifer typically yields water in quantities sufficient for commercial development and is <br />extensively utilized throughout the basin. Well yields may be as high as 100 gpm, but are <br />typically somewhat lower. Both the Laramie -Fox Hills and Arapahoe aquifers are generally <br />under artesian pressure at the present time. <br />PIERRE SHALE <br />The Pierre Shale underlies the Fox Hills Formation and is composed of up to 4,500 feet <br />of clay shale with minor sandstone units. In general, there is not sufficient water in the <br />intermittent sandstones for use in more than a single-family residence or possibly for the <br />watering of livestock. This formation defines the boundary for development of ground water for <br />commercial purposes in the Denver Basin. <br />3 <br />