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feet of colluviai soil consisting of brown to gray silty clay with occasional • <br />sandstone boulders. Colluvial soils are underlain by bedrock of the Mesa <br />Verde formation. Materials of the Mesa Verde formation consist of <br />sandstone, mudstone, coal with gray, stiff clay lenses, and shale. <br />Structural Geology <br />Geologic structure in the vicinity of the proposed refuse disposal area <br />conforms very well with the general district structure. There are very few <br />variations from the local strike and dip of the beds, which is N60W, 3° - 5° <br />Northeast. No major fault offsets have been found and to date, the <br />underground development shows no sign of major fault on slip-plane <br />structures. The only significant structures in the bedding planes are the <br />depositional contortions and undulations of the beds due to sandy channels <br />and fossilized fauna. <br />Seismicity <br />_ The refuse disposal area is in an area of minor or no seismic activity <br />belonging to Zone // 1 seismic risk as shown in Figure 1. This zone • <br />designation is for the entire state of Colorado and requires structures to <br />withstand static seismic loads of 0.05 g. Earthquakes of magnitude 5 or <br />above (Richter scale) have •occurred outside a 100-mile radius from the <br />mine. Stability analyses of the proposed refuse pile include the effects of <br />earthquake loading on the factor of safety. <br />,_ Hydrology <br />A discussion of the surface and subsurface hydrology of the environmental <br />study area can be found in Section 2.8 of the Mt. Gunnison M and R Plan. <br />The main sources of water in the vicinity of the proposed refuse disposal <br />area are snowmelt and rainfall. There are no watercourses flowing across <br />the surface of this area. <br />• <br />-6- <br />