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<br />t- <br />W <br />a'l <br />I-" <br /> <br />CHAPTER III <br /> <br />DESCRIPTION OF THE FIELD AREA <br /> <br />3.1 Location <br /> <br />The study area is located in Grand Valley, Colorado. It is <br /> <br />bounded by the Book Cliffs to the north, the Government Highline <br /> <br />Canal to the south, Mount Carfield to the east, and West Salt Creek <br /> <br />to the west (Fig. 1.1). The piedmont consists of an area of about <br /> <br /> <br />535 km2 of exposed Mancos Shale. pediments and alluvium (Fig. 3.1). <br /> <br />3.2 Geology <br /> <br />The Mancos Shale is a marine shale of upper Cretaceous age. <br /> <br />It is about 1200 m thick in the Grand Valley near Grand Junction, <br /> <br />Colorado (Fisher, et al., 1960). About 300 m of the formation is <br /> <br />exposed, and nearly all of the outcrop is north of the Highline Canal. <br /> <br />The remainder is covered by fan deposits. alluvium that is derived <br /> <br />from the Mancos Shale. and by, Colorado River alluvium (Schneider, <br /> <br />1975). <br /> <br />Within the study area. the Mancos Shale has a structural dip of <br /> <br />about 50N. It is characterized by zones of thin irregular layers <br /> <br />and overlapping lenses of calcareous sandstone, concretionary beds, <br /> <br />and limestone interbedded in shale. The thickness of the zones <br /> <br />range from 0.5 to 4 m and the groups are 8 to 60 m apart (Fisher, <br /> <br />et al., 1960). The zones are much more resistant than the enclosing <br /> <br />shale, and they crop out at times as cuestas. The shale surface is <br />