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<br />" '~ <br /> <br />" <br />~ <br />, <br />, <br /> <br />, <br /> <br />w <br />~ <br />t,~ <br />C.J1 <br /> <br />lenticular carbonaceous and coal-bearing shale and sandstone. The <br />soluble minerals contained within Mancos Shale, primarily sulfates of <br />calcium, magnesium, and sodium, comprise an average of two percent by <br />weight of weathered surficial shale. <br /> <br />',~ <br /> <br />~ <br /> <br />, <br />. 'j <br />1 <br /> <br />Climate, Vegetation, and Soils <br /> <br />The climate in the lowlands of the Upper Colorado River Basin is of <br />a semiarid continental type with frequent high intensity convective <br />storms of. small areal coverage (Fig. 1-7). Maximum monthly <br />precipitation occurs in July-August. In the 800k Cliffs desert, daily <br />and seasona:l temperatures vary widely with extremes of 42 to _4lo C <br />(Mundorff, 1972). The average potential evaporation measured with a <br />class-A pan at the Grand Junction airport is 233 em with a monthly <br />average of 46.5 em in July (Lusby, Reid, and Knipe, 1971). Mean annual <br />precipitation is 250 mm at Price, 200 mm at Woodside in the lower Price <br />Basin, and 215 mm at 8adger Wash near Grand Junction (Branson and Owen, <br />1970; Mundorff, 1972). <br />The crowns of living perennial plants cover less than 10 percent of <br />the surface except locally and there is less than 1 percent <br />vegetational cover on the steeper hillsides. Greasewood and rabbitbrush <br />grow on alluvial fills in the valley bottoms. Sagebrush is found on the <br />gravel-covered pediments below pinon-juniper stands on higher ground. <br />Mat saltbrush and shadscale dominate the barren Mancos Shale terrain. <br />Knobel et al (1955), Swenson et al (1970), Lusby et al (l971), and <br />SChafer (1981) have investigated and classified the soils derived from <br />and developed on Mancos Shale. These thin gray shale soils have a pH of <br />8.0, a bulk density of 1.3l-1.35 g/cm3 in the Al horizon, and a high <br />salinity. They contain montmorillonite, illite, chlorite, and mica. <br />Both fresh and somewhat weathered Mancos Shale swells oonsiderably when <br />wetted with a 25-50 percent volume increase in free swell tests (Schumm, <br />1964). <br />Data from small drainage basins on the Mancos Shale (Badger Wash) <br />were used by Langbein and Schumm (1958) to prove that semiarid regions <br />are those that produce the largest sediment yields per unit area (Fig. <br />1-8). The curve demonstrates that Mancos Shale terrain in western <br /> <br />, <br />^~ <br />o,~ <br /> <br />., <br /> <br /> <br />. ""-"',~ <br /> <br /> <br />13 <br />