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<br />12 <br /> <br />littered in many areas with fragments and plates of sandstone ranging <br /> <br />~-4 <br />c.v <br />OJ <br />w <br /> <br />up to 0.5 m in diameter and with fragments of concretions composed <br /> <br />of hard, dense impure limestone. <br /> <br />Badlands dominate the area. Amid the badlands are pediments <br /> <br />and alluvial deposits. The pediments are longitudinally concave- <br /> <br />upward, slope away from the cliffs and occur at no fewer than three <br /> <br />distinct elevations. Except for some of the alluvium in drainage <br /> <br />basins extending beyond the Book Cliffs, i.e., Big Salt Wash, Little <br /> <br />Salt Wash, East Salt Creek, and West Salt Creek, the alluvium is <br /> <br />derived almost entirely from weathered Mancos Shale and from the <br /> <br />pediments. <br /> <br />The Mancos Shale was deposited in shallow water of the Upper <br /> <br />Cretaceous Sea (Fisher, et aI., 1960). The shallow water environment <br /> <br />was conducive to the rapid evaporation of sea water and the resultant <br /> <br />precipitation of slightly to highly soluble minerals. The most abund- <br /> <br />ant soluble mineral in the study area is gypsum (CaS04 . 2H20), <br />with calcite (CaC03) next in abundance. Appreciable amounts of <br />sodium and magnesium hydrated sulfates and other carbonates are <br /> <br />present also. Chloride salts do not occur in appreciable amounts <br /> <br />(Laronne, 1977). <br /> <br />3.3 Climate and Vegetation <br /> <br />The climate is arid to semiarid. Annual precipitation normally <br /> <br />is less than 250 mm per year. Precipitation mainly occurs in the form <br /> <br />of snowfall in the winter months and as intense thunderstorms in the <br /> <br />summer months. Runoff from the Mancos Shale badlands occurs almost <br /> <br />exclusively as a result of high intensity thunderstorm events. Due to <br />