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<br />~ - - - .. <br />,---- <br />" <br /> <br />II <br />I <br />I <br />.- It <br />" <br /> <br />· Ii <br />r <br /> <br /> :! <br /> " <br /> :1 <br /> I <br /> 1 <br /> , <br /> 'i <br /> 'I <br /> !, <br /> 'I <br /> , <br /> II <br /> il <br /> II <br />. <br />'! <br />-~ .. , <br /> 'I <br /> " <br /> ,I <br /> ,I <br /> I <br /> <br />~. <br /> <br />" <br />, <br /> <br />000043 <br /> <br />- - - -- -- - -----. <br />--- ----- ------- <br /> <br />-10- <br /> <br />The South Platte River and its principal tributaries have <br /> <br />I, <br /> <br />incised a dendritic drainage pattern into thes,", bedl'ock formations' <br /> <br />to considerable depth. This pattern was subsequently bur ied by <br /> <br />later deposition of water and wind deposited sediments to depths <br /> <br />of 160 feet and more, Geologic evidence shows that in many Places, <br /> <br />the present flow channels of these streams are located at con- <br /> <br />siderable distance from the original channels they had cut into <br /> <br />the bedrocj<, This is true at the Narrows site. <br /> <br />It is apparent <br /> <br />that these streams wandered back and forth over the area as the <br /> <br />land to the west was uplifted during geologic time and vast <br /> <br />quantities of alluvium were brought in and deposited in these <br /> <br />" <br /> <br />lower channel arcas. <br /> <br />At present, bcdl'oeIl is exposed in only a <br /> <br />few places. <br /> <br />The overburden which was brought into this area was Chiefly <br /> <br />river alluvium consisting of sand and fine gravel. <br /> <br />In more re- <br /> <br />cent geologic time, wind deposition became mOl'e prominent, periods <br /> <br />of intense dust storms deposited layers of fine loessial silt and <br /> <br />fine sand in the form of dunes. <br /> <br />In most of the area the duues <br /> <br />and loess lie upon river sand and gravel, but in sane of the <br /> <br />higher areas they lie directly upon the bedrock fOl'mations. <br /> <br />Because of the highly pervious nature of the overburden <br /> <br />sediments and their great areal extent, they receive and store <br /> <br />lal'ge quantities of ground water. This water is derived from in- <br /> <br />filtration of irl'igation water, seepage from ditches and reser-' <br /> <br />voir, bed loss from streams and fl'om precipitation. This ground <br /> <br />water body fluctuates in volume with climatic conditions and with <br /> <br />the intensity of well pumping. When precipitation is high the <br /> <br />wells are pumped the least, and conversely; hence the water table <br /> <br />.., ,."', . <br />