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<br />. <br /> <br />. <br /> <br />~~.(.- <br />~j~J <br /> <br />Faults are also common, and several major faults are present in <br />the environs of the project area. Of these, the Ute Pass thrust <br />fault 3 miles west of the north end of the conduit course is the <br />nearest. At this location, the fault has thrust the Precambrian <br />rocks of the Front Range core over the hogback sedimentary sequence <br />so that the hogbacks are absent. Instead, Precambrian rocks are next <br />to the Pierre Shale, which underlies the hogback sequence and <br />generally outcrops east of it. Minor faults are also present <br />in the basin east of the mountain front. The conduit passes through <br />a valley eroded along such a fault in the first mile of its course. <br /> <br />The southwest flank of the Denver Basin underlies the project area. <br />This basin is deepest near Denver. It is asymetrical with steep <br />flanks along its western border and gentle dips on its eastern <br />flank. In the project area, the basin structure results in the <br />strike of the sedimentary formations swinging from north-south <br />near Colorado Springs around to northwest-southeast in the <br />Pueblo area. The structure brings the Niobrara Formation to the <br />surface in a wide outcrop band along the Arkansas River near <br />Pueblo. Erosion of this area has produced the limestone <br />capped bluff topography present in the south portion of the <br />conduit area. <br /> <br />The Pleistocene glacial epoch was the last of the major events <br />of the area's geologic history. Glacial meltwaters from successive <br />interglacial periods did their work of erosion and deposition. <br />In the project area, the plains surface was both spread with <br />alluvial deposits and further dissected. Some alluvial deposits <br />were moved and modified by wind. <br /> <br />b. Characteristics of Formations Present <br /> <br />. <br /> <br />Four Cretaceous formations outcrop in the project area. These are <br />the only consolidated rocks encountered. The conduit traverses a <br />short area of Dakota Sandstone after leaving the reservoir. The <br />Dakota Sandstone has medium permeability, excellent foundation <br />stability, and excellent erosion resistance. Excavation and <br />compaction are difficult. Slope stability is excellent except <br />rocks on dip slopes may slide if undercut. <br /> <br />111-4 <br />