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<br />C) <br />,,1 <br />..~ <br /> <br />No construction problems arise from the "bedrock" geology. <br /> <br />In brief, Rifle Creek cuts directly across the "Hogback", a steep <br /> <br />limb of a monocline where Mesa Verde sandstone, shale and coal <br /> <br />beds have been tilted nearly vertical, dipping 800 to 850 down- <br /> <br />stream. The sandstones are hard but somewhat friable, the <br /> <br />intervening shales firm and impervious. The harder sandstone <br /> <br />ribs, therefore, form the ridges between ;1 devil I s slides", <br /> <br />where the softer shale has been more deeply eroded. The sand- <br /> <br />stone ridges run at right angles to or directly across the <br /> <br />valley and are of varying thickness (II to 20l). This rock <br /> <br />series is not unusually fractured or broken but the sandstone <br /> <br />beds are jointed thereby becoming somewhat permeable. The <br /> <br />alternating tight shale beds, however, should form excellent <br /> <br />H cut-off" members to water attempting to bypass either rock <br /> <br />abutment or the rock foundation. Only one small fault was <br /> <br />identified in the valley, a small displacement cutting <br /> <br />diagonally across the valley below the selected axis. It will <br /> <br />not affect the site concerned. <br /> <br />63 <br />