2010-04-26_PERMIT FILE - C1980007A (14)

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2.0 General Environmental Setting 0 The following section describes mapped and documented data on the project area, including geology, hydrology, mapped soil units, and available natural vegetative community data. 2.1 Geology "No Name Gulch" project area bedrock is primarily composed of sandstone, and secondarily by shale. Both are sedimentary rocks composed of sand -sized or finer (silt or clay) minerals. The geologic unit primary to the project area is Mesaverde FM, Undivided, which originated in the Cretaceous period. It is noted for containing major coal beds or seams, with coal being the tertiary rock underlying the sandstone and shale (USGS 1992). The project area ranges in elevation from approximately 6,100 feet above mean sea level (AMSL), at the northwest corner, to approximately 7,940 feet AMSL at the southeast corner, as shown in the topographic map in Figure 3. The side slopes of the Gulch are very steep, averaging 40 -60° or more, and extend for a distance of approximately one - quarter mile from top to bottom. The thalweg of the gulch is only slightly less steep, ranging from 30 -50 °, and extends for approximately one mile, from the highest crest in the south to the lowest point in the north, near the North Fork Gunnison River. Photos of the east and west slopes and thalweg of "No Name Gulch" are included in Appendix A. 2.2 Hydrology The "No Name Gulch" project area drains south to north towards the North Fork Gunnison River. One 42 -inch culvert beneath Highway 133 allows for drainage from the gulch to the North Fork Gunnison River. A visual inspection of the vegetation, drainage patterns, and sedimentation in the culvert and connecting ditches indicates that the culvert and ditches do not appear to convey a lot of water, and may even be effectively blocked by spoil side cast resulting from onsite road construction. As a whole, the "No Name Gulch" project area is somewhat xeric, especially in higher reaches. The most significant source of water in the gulch is most likely snowmelt. The U.S. Geological Survey Quadrangle map ( "Somerset" Quad) (Figure 4) indicates that the center of the gulch is intermittently flowing. It stands to reason that most of the year, the thalweg of the gulch would be mesic to dry, but during the late spring and early summer, as snowmelt runs down the gulch, collecting in the thalweg, the lower (northernmost) reaches of the thalweg may experience muddy conditions and seasonal flow, that may or may not ultimately reach the culvert and North Fork Gunnison River. In addition to rainfall, another source of hydrology, albeit very minor, includes the occasional subsurficial flow of