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t t&ttttttttttttttttt t a &ttttttLAA1Att& a t I I t1ttl1iiiiiiij 14 344441449 a 11V <br />Colorado Geological Survey GROUND -WATER ATLAS OF COLORADO <br />Ps. 8 DAKOTA- CHEYENNE <br />AQU /FER <br />The Dakota — Cheyenne Group is an assem- <br />blage of sandstones, shales, and mudstones <br />of lower Cretaceous age that were typically <br />deposited in deltaic environments along an <br />ancient seaway that covered much of <br />Colorado during the Cretaceous period. <br />The Dakota - Cheyenne aquifer consists of <br />water - yielding, clastic sedimentary rocks of <br />the Dakota Sandstone/ Dakota Group and <br />the underlying Cheyenne Sandstone <br />Member of the Purgatoire Formation. The <br />aquifer is present throughout most of <br />Colorado, and is an important aquifer in <br />many locations (Figure 6.8 -1). Where these <br />units are close to the surface, the Dakota - <br />Cheyenne aquifer is the most extensive <br />water - yielding unit in eastern Colorado <br />(Robson and Banta, 1987). <br />Commercial quantities of hydrocarbon, <br />geothermal, coal, and coalbed methane <br />resources are also present in these geologic <br />units, particularly in the Denver- Julesburg <br />Basin of northeastern Colorado. It is esti- <br />mated that up to 31 percent of the state's oil <br />and 25 percent of its natural gas have been <br />produced from the Dakota Group (Pearl, <br />1982). Although not developed, geothermal <br />potentials are high in the Canon City <br />embayment area of south - central Colorado. <br />In addition, high - quality coal has historical- <br />ly been produced from the Nucla - Naturita <br />field in southwestern Colorado. <br />Figure 6.8 -I. Location and extent <br />of the Dakota — Cheyenne aquifer, outside <br />of designated basins and the <br />High Plains aquifer, showing the <br />distribution of permitted water wells. <br />D 100 Miles <br />�g �a ,� Bey (Survey <br />100 meter Digital Elevation Model courtesy of U. S. Geological Survey <br />EXPLANATION <br />Dakota — Cheyenne <br />aquifer boundary <br />• Wells used in <br />USGS related <br />investigations <br />0 Wells of record <br />in DWR permit <br />database <br />