Limestone-Graveyard Creeks Watershed Plan and Environmental Assessment

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L i OG46 PROJECT SETTING ' Location and Size The Limestone - Graveyard Creeks Watershed is located in eastern Bent and ' western Prowers Counties in Southeastern Colorado. The watershed consists of 59,250 acres and averages about 5 miles wide and 16 miles long. Lamar, Colorado is on the east edge and Las Animas is slightly ' west of the watershed. Pueblo, Colorado is 100 miles west of the watershed area. The watershed is bounded on the the Fort Lyon Canal, east by the the Arkansas River. It includes Prowers Arroyo, Pleasant Valley Arkans River. west by the Prowers Arroyo, north Pleasant Valley Drain, and south Limestone and Graveyard Creeks, and Wiley Drains which outlet into by by the i Topoc y and Drainaae The highest elevation in the watershed is the Fort Lyon Canal. It varies from an elevation of 3950 ft. on the west edge to 3860 ft. on the east edge. The Arkansas River, or southern boundary, is the lowest elevation in the watershed. It varies from 3740 ft. at the west edge to 3630 ft. at the east edge. The watershed is gently sloping with approximately 1/2 of the drop in elevation occurring below the irrigation area in the final mile as the drainages enter the Arkansas River ' _ley. ' The drainages of the watershed all outlet into the Arkansas River. Prowers Arroyo, Limestone Creek, Graveyard Creek, Wiley Drain, and Pleasant Valley Drain all have small year around flows. ' Geolocry 1 / The watershed is located within the Colorado Piedment Section of the Great Plains Physiographic Province (Fenneman, 1931) . The Colorado Piedmont represents an old erosion surface. It is a mature to old, broadly rolling, elevated plain with local scarps. Bedrock consists primarily of cretaceous marine shales and limestones. These formations dip slightly to the northwest, toward the Denver structural basin. The oldest formation that crops out in the watershed is the Lower Cretaceous Dakota sandstone, which is found along the valley side above the Arkansas River flood plain. Overlying the Dakota Formation (from oldest to youngest) is the Graneros shale, Greenhorn limestone, Carlile shale, and the Fort Hays limestone member of the Niobrara Formation. Younger Quaternary deposits overlay the bedrock over much of the watershed area. Shales and limestones have higher concentrations of some minerals than other rock types have. This is particularly true of minerals such as sulfur and trace minerals such as arsenic, boron, and selenium (Turekian and Wedepohl, 1961). 8