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<br />~ <br />tAl <br />c.n <br />0) <br /> <br />5 <br /> <br />derived from mudflows and slurries on the basalt-capped escarpment <br /> <br />associated with the melting of glaciers following four Pleistocene glacial <br /> <br />episodes. Sinnock also contends that no comparable mudflows occurred <br /> <br />in Grand Valley due to a lack of glaciation, or a resistant caprock in <br /> <br />the Book Cliffs. <br /> <br />Runoff and sediment yield from hillslopes have been studied by <br /> <br />several investigators over the past three decades. All have indicated <br /> <br />that runoff and associated hillslope erosiop. occur almost wholly in <br /> <br />response to high intensity summer thunderstorms (Schumm, 1964; <br /> <br />Schumm, 1967; Hadley and Lusby, 1967; Lusby, et a!., 1971; Bureau <br /> <br />of Land Management, 1978). Schumm (1964) and Lusby, et a!. (1971) <br /> <br />conducted studies in Badger Wash near Mack, Colorado, and observed <br /> <br />the importance of seasonal variations on, hillslope processes. They <br /> <br />noted the seasonal cycle of rill development and obliteration in conjunc- <br /> <br />tion with summer thunderstorms and winter frost heave of the surficial <br /> <br />materials, respecti vel y . <br /> <br />Based on hillslope measurements, Schumm (1964) concluded that <br /> <br />the typical concave-convex hillslopes that have developed on the Mancos <br /> <br />Shale are fashioned primarily by soil creep. That is, soil creep is <br /> <br />a product of frost heave and gravity and entails the movement of <br /> <br />soil from the convex portion over the steep portion, with soil accumu- <br /> <br />lation on the concave portion. Schumm also reasoned that where <br /> <br />creep is the dominant process, the greatest removal of material occurs <br /> <br />on the upper part of the hillslopes, and that the fastest rates of <br /> <br />soil movement are on the steepest portions of the slopes. <br /> <br />Hadley and Lusby (1967) had the opportunity to measure the <br /> <br />erosional effects of a high intensity thunderstorm in a small basin in <br />