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<br />. <br /> <br />. <br /> <br />. <br /> <br />.. r' G~.' <br />, ., ~. <br />I.., v ~ <br /> <br />GENERAL INFORMATION <br /> <br />Location <br /> <br />The Narrows Unit is located in northeastern Colorado with the <br />service area extending along the South Platte River from the vicinity <br />of Narrows Dam above Fort Morgan, Colorado, to the Colorado-Nebraska <br />state line. Parts of Weld, Morgan, Logan, Washington, and Sedgwick <br />Counties are included in the Unit. Principal towns are Fort Morgan, <br />Brush, Sterling, and Julesburg, The location is shown on the General <br />Map, Exhibit 1. <br /> <br />Geology <br /> <br />Geological investigations for a damsite in the vicinity of <br />Fort Morgan, Colorado, covered a 30-mile reach of the South Platte <br />River. The Corps of Engineers made investigations of the Narrows <br />and Fort Morgan sites in 1943 and 1944 with Bureau of Reclamation <br />technical and drilling personnel conducting the foundation and <br />materials investigations. Subsequent to allocation of funds for <br />the Narrows Dam in 1947, geological studies were initiated by the <br />Bureau of Reclamation as a part of the general investigations which <br />resulted in the selection of Narrows damsite. <br /> <br />Regional Geology <br /> <br />The South Platte River flows through a broad, featureless <br />valley characterized by two to four old terraces and there are few <br />firm bedrock outcrops, Where found, the outcrops are Pierre shale. <br />At depth, this shale consists of dense claystones and siltstones <br />which, on exposure, weather to a soft, muddy clay. <br /> <br />Water wells and exploratory drilling have indicated the <br />presence of a deep ancestral river valley in the Pierre shale, <br />now filled with loose, mainly alluvial, sediments. The thalwegs <br />of the old and the present channels are at varying distances from <br />each other, ranging from two to four miles but intersecting in <br />some instances, The older channel lies south of the present <br />channel at the Narrows site. <br /> <br />2 <br />