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thunder storms. The summer storms frequently become localized within the Basin, <br /> resulting in flash flooding, debris flows or small landslides. <br /> The mines were driven into coal seams occurring in the basal portion of the Mesaverde <br /> Group. The Mesaverde group is a near shore marine unit consisting of interbedded <br /> sandstone, shale and coal. Mesaverde coal is commonly mined throughout western <br /> Colorado. However, Coal Basin coal is unique in that it has been slightly <br /> metamorphosed as a result of the nearby West Elk laccolithic intrusion. Because the <br /> coal was slightly metamorphosed, it is ranked as anthracitic, thus making it suitable for <br /> steel manufacturing, an unusual quality in the western coal fields. <br /> The Mine Bench Outslopes are long, steep, relatively unconsolidated fills which were <br /> created as a result of mining operations. The Outslopes are generally composed of <br /> sandstone, shale and coal particles which have been pushed or shot from the overlying <br /> Mine Bench or mine entry areas. Trommel reject as well as run-of-mine reject materials, <br /> trash and debris are commonly found interspersed with the other materials. Particle <br /> sizes vary from approximately silt to cobble. <br /> The top of each Mine Bench Outslope is located at an elevation of about 10,000 feet. <br /> Commonly the outslopes are 800 - 900 feet in length and reside at the angle of repose. <br /> The slopes vary in size from three tenths of an acre to over eight acres each. Excepting <br /> vegetative test plots and other experimental work, the Outslopes are generally devoid of <br /> vegetation. Soils are essentially non-existent on the slopes. Each outslope is subject to <br /> significant erosion, as evidenced by the well developed gullies which are common. <br /> Quantitative measurements of sediment generation from the various slopes have not <br /> been made. It is apparent that the timing of sediment delivery from the outslopes to the <br /> adjacent streams is coincident with spring snow melt and runoff from rain events. Visual <br /> observations confirm that the Mine Bench Outslopes are significant areas of sediment <br /> generation. Models of sediment generation indicate that 7.2 to 11.3 tons per acre of <br /> sediment are shed from the Outslopes annually. The sediment generated from the site <br /> is believed to be high in iron, as much of the Mine Bench Outslope material is pyritic. <br /> The rate of erosion of this material suggests that it is a contributory source of iron to <br /> Coal Creek. <br />