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<br />. <br /> <br />Deadhorse Creek Watershed <br />October 25, 1996 <br /> <br />an orthoquartzite. <br /> <br />Several areas of biotite gneiss are mapped near the junction of <br />Deadhorse and the Colorado River. Both East and West Deadhorse <br />Creek are filled with alluival and/or colluvial materials which <br />covers some inferred faulting. The gneiss is layered, sometimes <br />coarse-grained with 1 inch aggregates of muscovite, migmatitic, and <br />composed of quartz, orthoclase, plagioclase, biotite, and musco- <br />vite. <br /> <br />The permeability of these units is in large part dependent upon the <br />mineralogical composition. The clastic and carbonate rocks gener- <br />ally are highly permeable to water flow. Orthoquartzites typically <br />are relatively free of or lack a fine-grained matrix, but non-per- <br />meable. The units in Deadhorse Creek are typically an interbedded <br />complex of shales, claystones, siltstones, sandstones, limestones, <br />and dolomites. The Sawatch quartzite is a 500 foot thick package <br />of mainly orthoquartzite except for a thin arkosic-conglomerate <br />member at the base. The Sawatch has been subjected to crustal <br />stresses which have created fractures or conduits which probably <br />extend for great distances both vertically and horizontally. Bed- <br />ding planes probably provide other internal flow paths for water. <br /> <br />tit The Quaternary units include alluvium, colluvium, and talus. An <br />unique chemical precipitate unit forms the dam for Hanging Lake. <br />This unit is derived from a combination of mineral-charged spring, <br />ground, and surface water. These units are not shown on the four <br />exhibits except for the precipitate unit at Hanging Lake. <br /> <br />The Grizzly Creek Fault forms a semi-circle around the southern end <br />of the White River Uplift. This normal fault crosses the Deadhorse <br />drainage about ls mile to the northwest of Hanging Lake. There are <br />numerous other inferred faults in the area (Kirkham and others, <br />1996). These inferred faults are easily erodible zones of varied <br />width and depth are the primary reason for the location of the <br />creeks. In the East Fork, an inferred fault starts at Hanging Lake <br />and continues downstream to about the 6,900 foot contour. A short <br />section of inferred fault is located north of Hanging Lake between <br />stations DS 4A and DS 5 and continues to the southeast up the east <br />side of the canyon. There are two inferred faults in the West <br />Fork. One follows the drainage from the GCF downstream to about <br />the 7,200 foot contour. A second fault strikes eastward from the <br />GCF terminating in the West Fork at about the 7,450 foot contour. <br />These inferred faults are capable of carrying water to depth into <br />the arkosic member of the Sawatch Quartzite at a lower elevation. <br />The Sawatch has been either terminated, shortened, or obscured in <br />part by each of these faults. <br /> <br />e <br /> <br />2 <br />