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ALLUVIAL VALLEY FLOOR DETERMINATION <br />MCCLANE CANYON MINE <br />COAL MINE WASTE PILE <br />GARFIELD COUNTY, COLORADO <br />In the investigation area, alluvium associated with the active channel of the East Salt <br />Creek and older alluvium was observed and mapped; it extends a limited distance east of <br />the creek to where the alluvium is covered by younger deposits (Figure 2 and Photo 6). <br />Landslide Deposit <br />A large deposit that overlies all other deposits was identified during the site visits <br />(Figure 2). The nearly flat, elliptical-shaped deposit is approximately 6 to 15 feet higher <br />than the adjacent deposits and extends eastward across the valley from East Salt Creek to <br />nearly the canyon wall. The deposit is composed of dense silty sand with areas of <br />medium- to coarse-grained angular gravel. A few random angular cobble-sized rocks <br />were observed. Similar deposits were observed on the west side of the creek, but <br />contained a higher concentration of angular rocks, some up to boulder-size. The highway <br />cuts through this deposit, and on the west side of the road the deposit contains larger <br />angular rocks that overlie finer-grained material. <br />The shape, orientation, and lithology of the deposit indicates that it is most likely the <br />result of a large landslide from the west wall of the canyon. Most of the larger material <br />came to rest at the base of the west canyon wall (west of East Salt Creek), and the more <br />fluid fraction "ran out" to the east across the valley. There is an area of large boulders <br />within the active channel where the landslide crossed the creek, unlike other portions of <br />the active channel that contain few large boulders (Photo 6). The area of large boulders <br />could be the result of the creek removing most of the finer material after breeching the <br />landslide, leaving only the larger rocks. However, it is possible this material is not <br />natural and was placed as riprap during construction of the diversion structure. <br />The landslide deposit was reported to be the result of man-made fill in the McClane <br />Canyon permit application package (permit No. C-1980-004) to the DRMS. However, <br />there is no obvious reason for such a large artificial embankment. The builders of the <br />historical water diversion most likely used the constricted area of the creek to their <br />advantage, but the diversion required only an increase of a few feet in elevation to divert <br />water, rather than the 20 feet or more of the deposit. In addition, there is no evidence of a <br />borrow area for this significant volume of material. The uniformity of the material <br />4 <br />ERO <br />Resources <br />Corporation