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<br />3.0 GFpLCGIC SETTING <br />The uppermost bedrock in the area is undifYerentiated Mesaverde sandstone. <br />The bedrock dips slightly to the northeast, forms high mesas away from the <br />river, and has been highly dissected and eroded by the Colorado River and <br />tributary streams in the vicinity of Rapid and Cottonwood Creeks. The <br />bedrock surface along the lower part of Rapid Creek is buried and irregular, <br />as evidenced by the presence of a few bedrock outcrops at varying <br />elevations. <br />Fan deposits originating from Grand Mesa to the east and transported through <br />the Rapid Creek drainage cover most of the bedrock ir. the project area. <br />C • These deposits have beer, eroded by the Colorado River and Rapid Creek, and <br /> are evident as terrace surfaces that slope to the west and southwest. <br />Remnants of alluvial sand and gravel deposits originating from the Corrado <br />River are found on the terrace surfaces. Terraces C and D are covered with <br />sandy loam soil with little gravel composition, indicating possible loess <br />deposits. <br />The geologic history of the area includes a complex sequence of structural <br />uplift, mass wasting of upland deposits, Colorado River channel downcutting <br />and deposition, and Rapid Creek channel erosion. The exact sequence of <br />erosion and deposition is beyond the scope of this investigation. However, <br />the composition, transport mechanism, and extent of the unconsolidated <br />deposits are important in identiYy*ing the presence oY AYF. Therefore, the <br />• fan and alluvial sand and gravel deposits are each discussed in more detail <br />6 <br />Hydro-Search, It1C. Reno • Derner • Austin cormi~ruc rnoao~ocnn-cFaocis~s <br />