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BRUCE FLOROUIST, P.E. - ENGINEERING GEOLO:"1ST <br />17697 U.S. HIGHWAY 550, MONTROSE, CO 81401 <br />• 303249.4142 <br />SITE GEOLOGY <br />~- <br />The geology of the site is relatively simple. It consists <br />entirely of sandstones and shales of the Mesa Verde Group which <br />is covered locally with up to 26 feet of alluvial and colluvial <br />material that is locally derived. The beds strike „ st-west and <br />dip 50 to 55 degrees south. This particular monocl>,n.,l. structure <br />i.s known as the Grand Hogback and Harvey Gap is a breach in that <br />Hogback. The walls of the valley consist of exposed to s].iyi,Lly <br />weathered sandstones, siltstones and shales. The central part of <br />the valley contains the alluvial and colluvial material which <br />were deposited at a time when the main Harvey Gap drainage w~,s <br />also in a depositional phase. The main drainage in recent <br />geologic time has been undergoing headward erosion, but this <br />process was apparently arrested by the constructic.., of the Grass <br />:alley Dam and Reservoir which now controls any floodwaters in <br />the main channel. <br />The site is very stab).e in terms of geologic hazards. 7l,ere <br />is no evidence of any landslides, mudflows or other major gravity <br />related movements with the exception of some rockfalls that are a <br />product of the higher exposed sandstone and the steep terrain. <br />• The site is not now and wit]. not in the future be subject to <br />:,ubsidence occasioned by past or prusent mining ac t:,vity. None, <br />of the previous mines appeared to have mined downdip which is th,• <br />only way that this site could be empi:ri.led. Also, thc• new East <br />Side mine is just that, on the East Side of the drainage and <br />there are no plans at this time to ever mine back under this: <br />valley. There are two primary reasons for this. First, The East <br />Side mine will be mining a seam that is up-section from this sites <br />and further, she only seam that could ever affect this site has ~ <br />Z foot thick split of sandstone and shale that would make future <br />mining under this site very unlikely. <br />SUMMARY: <br />''he site appears to be well suited for the intended pu,.pose <br />of spoil disposal as it is near the portal of the East Side Mine <br />but yet in a structurally sa`e place that wi].1 not interfer with <br />nor be affected by activities at the East Side ;:ine. In short, <br />there ar'.cars no reason to preclude construction of the spoil <br />pile at ~r,e subject site. <br />BRUCE A. FLORQUIST, P.E. <br />~ ~ ~/~ <br />~ iys~iz <br />G <br />