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<br />40 <br /> <br />and bank failure. In relative terms, badlands underlain by inter- <br /> <br />...... <br />c.u <br />CD <br />jl-" <br /> <br />bedded shale and sandstone bedrock are more stable than those <br /> <br />underlain by shale bedrock. The former are less erodible because <br /> <br />they have a more permeable soil layer which gives rise to deeper <br /> <br />soils and greater, though minimal, vegetative cover than the latter. <br /> <br />5.3 Pediments <br /> <br />5.3.1 Introduction <br /> <br />The area has many generally smooth, sloping, gravel- <br /> <br />capped landforms perched above the badland terrain. These features <br /> <br />are common along other portions of the Book Cliffs as well as in <br /> <br />other areas where Mancos Shale crops out below resistant cliffs. These <br /> <br />landforms are referred to as pediments. <br /> <br />By definition, a pediment is a gently inclined planate erosion <br /> <br />surface carved in bedrock and generally veneered with fluvial gravels <br /> <br />(American Geological Institute, 1976). Many theories have been <br /> <br />developed to describe the origin of pediments, but none apply to the <br /> <br />pediments in Grand Valley. For example, there is no evidence of <br /> <br />lateral swinging of streams issuing from mountains, as Gilbert noted <br /> <br />(1877). Rich's (1935) conclusion that weathering and sheetwash are <br /> <br />the principal pediment-forming agents does not apply. The theory <br /> <br />offered by Rich (1935), Hunt, et al. (1953), Godfrey (1968), and <br /> <br />Carter (1980) that stream capture caused the multiple surface levels <br /> <br />does not pertain to Grand Valley, either. Sinnock's (1981) observa- <br /> <br />tions are more applicable than other theories, with the notable excep- <br /> <br />tion that Grand Valley pediments are not capped by glacial outwash <br /> <br />and mudflows. <br />