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<br />n" 1 I' (' <br />YiUc"tlC <br /> <br />Occurrence of Ground water in the Ogallala and <br />several consolidated formations in Colorado <br />A repOrt to the Ground-water Codification and <br />Research Studies co~~itteo <br /> <br />by <br /> <br />Edward A. Moulder <br /> <br />/ <br /> <br />The aquifers herein discussed differ from the alluvial <br />aqu~fers along the principal streams. Withdrawals from these <br />aquifers have littte effect on the surface-water resources of <br />Colorado compared to those from the alluvial aquifers of the <br />Soutb Platte, Arkansas, and San Luis Valleys. The Ogallala <br />formation of Pliocene age ~eceives little recharge from streams <br />and contributes little water to streams in Colorado. '!'he <br />perennial streams are in contact with tile Ogallala ancl the <br />principal consolidated water-bearing formations in colorado <br />onl.y where they cross.. the outcrops of the fo~mations; the <br />contact area is small comoared to the areal extent of the <br />aquifers. Therefore, in most areas, it may be possible, frolll <br />a practical standpoint, to satisfsctorily develop and manage <br />the ground-water resources of these aquifers independent of <br />the surface water. <br /> <br />Biqh plains sQUif;er.--Of the four major ground-water <br />provinces in Colorado (SOuth Platte Valley, Arkansas Valley, <br />San Luis Valley, and High Plains), the High Plains province <br />is the largest. Xt covers about 12,000 square miles, including <br />all or parts of 15 counties in eastern Colorado. The province <br />has been separated into three major parts by Big Sandy Creek <br />and the Arkansas River. The largest part is northeast of <br />Big Sandy creek and centers around Yuma County. 'l'he put <br />southwest of Big Sandy Creek is irregularly shaped, being eroded, <br />in part, by tributaries t.o the Big Sandy and the Arkansas. 'l'he <br />third part lies south of the Arkansas in the southeast corner <br />of the state. <br /> <br />Deposits of the Ogallala formation mar~ up the surface <br />of the High Plains and form the aquifer. However, a part of <br />the Ogallala formation is overlain by younger windblown deposits <br />generally lesa than 50 feat thick. The Ogallala consists <br />chiefly of sand and gravel, although it contains numerous beds <br />of finer grained material consisting of clay, silt, cemented <br />sand, and limestone. In a few places the formation is IlIOre <br />than 400 feet thick, but more generally it ranges in thickness <br />from 200 to 300 feet. From one-third to one-half of the <br />material is saturated with ground water. <br />