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6 Geology <br />The project site is located on the western slope of the Rocky Mountains in western Colorado near the <br />boundary between the Rocky Mountain and Colorado Plateau physiographic provinces. Layers of <br />sedimentary deposits flank the northern slopes of the laccolithic West Elk Mountains. These <br />sedimentary rocks were deposited in both the deep and shoreline areas of a shallow inland sea that <br />encroached on western Colorado starting in the Cretaceous period. <br />The site is near the contact of the Mancos Shale and the overlying Mesaverde Formation. Mancos <br />Shale and Mesaverde Formation deposits are nearly horizontal, and dip only slightly to the north and <br />east in the vicinity of the site. The contact between these formations is exposed about 2,000 feet <br />downstream of Monument Dam. <br />The topography near the dam is controlled by the hard, cliff-forming sandstone members of the <br />Mesaverde Formation and the softer siltstone and shale members, which can only maintain relatively <br />flat slopes. Many landslides and debris avalanches, however, are present downstream of and on both <br />sides of the dam. <br />For a more detailed description of the regional and site geology, see the Report of Geotechnical <br />Investigation Conducted at Monument Dam (Barr, 2007),. which is included in Appendix A. <br />P:\Mpls\06 CO\26\0626067\WorkFiles\DesignReport\FINAL\DesignReportFINAL.doc 11 <br />