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<br />41 <br /> <br />5.3.2 <br /> <br />Theory of Pediment Origin <br /> <br />,.... <br />w <br />c.o <br />N <br /> <br />Comparison of studies of pediment origin conducted <br /> <br />by Gilbert (1877), Rich (1935), Hunt (1953), Godfrey (1968), Carter <br />(1980), and Sinnock (1981) suggests that landforms identified as <br /> <br />pediments may have developed by different processes in different <br /> <br />areas. Pediments in the study area, although similar in appearance <br /> <br />to pediments described in other areas, appear to have developed by <br /> <br />a series of events unlike those described elsewhere. For example: <br /> <br />1) the present piedmont is composed of badlands formed by head- <br /> <br />ward extending drainages of ephemeral streams as opposed to being <br /> <br />laterally planated by upland-derived streams; 2) no pediments are <br /> <br />positionally associated with upland stream drainage basins; 3) the <br /> <br />pediment surfaces contain numerous boulders up to 4 m in diameter <br /> <br />which are too large to have been deposited by stream flow (note <br /> <br />point (2)); and 4) stream capture is not an important mechanism. <br /> <br />Mapping directly onto topographic maps with the aid of aerial <br /> <br />photographs proved to be a valuable tool in understanding the nature <br /> <br />of the pediments (refer to Fig. 7.2). The lowermost pediment <br /> <br />surfaces are the closest to the Book CHff escarpment. Presently, <br /> <br />the upper reaches of most of the surfaces are within 1 km of the <br /> <br />escarpment. Such close proximity to the cliffs prevents the theory <br /> <br /> <br />of fluvial deposition of gravels from applying to these surfaces. <br /> <br />Also, the topographic maps indicated that all of the pediments in <br /> <br />close proximity to the cliffs are associated with large cirque-'like <br /> <br />hollows in the cliffs. The hollows probably represent the locations <br /> <br />of massive rock slides in the past, although the arid erosional en- <br /> <br />vironment has removed any physical evidence along the escarpment. <br />