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correspond to the Dakota and Cheyenne formations respectively. Depending upon <br />location within the District and stratigraphic variations of the intervening shale aquitards, <br />these three aquifers may contain perched zones related to differential or seasonal <br />distribution of surficial recharge. These small and generally isolated areas may account <br />for some of the limited water reported in some domestic wells. <br />6.3.2 High Plains Aquifer <br />The High Plains aquifer is the upper -most aquifer in the Basin. Geologically, it includes <br />Quaternary -age alluvium and eolian sediments in the Basin and the Tertiary -age <br />Ogallala Formation. In Colorado, the Quaternary sediments are generally less important <br />as a source of ground water than in Kansas. These surficial deposits are mentioned as <br />hydrostratigraphic units only because they are a primary upper medium through which <br />precipitation, surface runoff, and in some cases, irrigation return flows are recharged to <br />aquifers. Some shallow domestic or stock wells may also produce from the alluvium. <br />Several shallow, high-capacity irrigation wells are completed in the sands and gravels of <br />Quaternary alluvium in the canyon bottoms of southwestern Baca County, (see monitor <br />well numbers 5233 and 5238 in Figure 1, Cross-section A -A'). There are also several <br />alluvial irrigation wells along the Cimarron River in the southeastern corner of Baca <br />County and at numerous places along Bear Creek, near Springfield and near the Kansas <br />state line. <br />The eolian deposits are widespread in southern Baca County and are generally above <br />the water table. These silty to sandy deposits may be important catchment areas and <br />avenues for recharge of precipitation to the underlying Ogallala Formation from <br />precipitation. <br />The High Plains Aquifer underlies eight states and 156,000 square miles and is the most <br />significant aquifer in the High Plains geographic area. The Ogallala Formation is the <br />predominant member of the High Plains Aquifer in eastern Colorado. It is correlative <br />with the Ogallala Formation of Kansas and other neighboring states. <br />The saturated thickness of the High Plains Aquifer is shown on Map 4 as five distinct <br />and separated areas, especially in the northeastern part of the District where the aquifer <br />is thinner and largely depleted. As shown in the cross-sections (Figures 1 through 5), <br />the High Plains Aquifer has been depleted across most of the District. Five areas in the <br />District have water saturation remaining in the High Plains Aquifer. In each of these <br />areas the aquifer appears to be recharged by the underlying aquifer in addition to <br />VI 7 <br />99-028.003\Phase 2 Report\Hydrogeology <br />