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<br />.- <br />W <br />.+:0. <br />CJl <br /> <br />ABSTRACT <br /> <br />GEOMORPHIC AND LITHOLOGIC CONTROLS OF <br />DIFFUSE-SOURCE SALINITY, <br />GRAND VALLEY, WESTERN COLORADO <br /> <br />The Mancos Shale, composed of a thick sequence of interbedded <br /> <br />shale and sandstone, is known to be a significant contributor of dis- <br /> <br />solved solids to the upper Colorado River. Several ephemeral stream <br /> <br />tributaries of the Colorado River cross or have their sources on <br /> <br />exposures of Mancos Shale at the base of the Book Cliffs in Grand <br /> <br />Valley, western Colorado. The purpose of this investigation was to: <br /> <br />1) describe the geomorphology of the area; 2) describe soluble <br /> <br />mineral content relationships of surficial materials in erosionally <br /> <br />unstable landforms; 3) relate geomorphic stability to processes of <br /> <br />salt release from the area; and 4) recommend land u!jle and/or salt <br /> <br />control measures that might be employed for the purpose of reducing <br /> <br />the salt load entering the Colorado River. <br /> <br />The study area consists of three landforms: badlands, pedi- <br /> <br />ments, and alluvial valley floors. The badlands comprise the greatest <br /> <br />surface area. Soil depth and soluble mineral content of surficial <br /> <br />materials vary with the two dominant bedrock types in the area. <br /> <br />Research locations underlain by interbedded shale and sandstone have <br /> <br />. <br /> <br />significantly greater soil depth and significantly lower soluble mineral <br /> <br />contents than do locations underlain by mostly shale. The badlands <br /> <br />are the least stable landform, and they release more sediment and salt <br /> <br />into runoff than the other landforms. <br /> <br />.ii <br />