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landslide areas typically have flat slopes, a hummocky <br />• topography, local depressions lacking dtainage, and usually <br />a dense vegetation. <br />Several landslides identified in the area are recent; <br />some of them may be related to human activity, specifically <br />to mining. They will be dealt with in detail in Section 2.4 <br />2.2 GEOLOGY <br />Important stratigcaphy of this study area consists of <br />the lower 1,500 feet of the hSesaverde Formation, of Upper <br />Cretaceous Age (Plate 1). The hlesaverde consists of <br />interbedded sandstones, siltstones, shales, and coals. CWI <br />(1983) describes the t4esaverde as predominantly sandstone in <br />the southern portion of the area, grading into shales in the <br />northern portion. The sandstones are generally light grey, <br />fine grained,shaley or silty, and interfinger with adjacent <br />shales. The shales are grey to black and generally <br />carbonaceous. P7any uneconomic thin, irregular coal seams are <br />interbedded with the shales and sandstones. <br />There are four members within the Mesaverde in the <br />area. The lowermost member consists of the Rollins <br />Sandstone, a cliff-forming, light colored sandstone 150 to <br />• 200 feet thick. The Lower Coal Member ranges from 125 to 900 <br />feet in thickness, and is characteristically shale in the <br />lower portion and sandstone in the upper portion. The A-coal <br />seam lies immediately above the Rollins Sandstone Member, as <br />a generally thin, dirty coal. The B- and C-seams lie higher <br />in the Lower Coal Member. The B-seam, although not <br />economically mineable in the lease area, is mined in areas <br />to the northeast. The C-seam is economically mineable in <br />this region, but is not presently mined at Orchard Valley <br />Mine. Interbedded sandstones and shales tend to me more <br />lenticular in the Upper Coal Member, which ranges from 400 <br />to 600 feet in thickness. The Upper Coal Member contains the <br />D-seam, which is presently worked at Orchard Valley h1ine and <br />will be mined in the lease area. Plate 2 shows structural <br />geology and the location of sections across the lease area. <br />Plates 3 through 6 show in sections the position of the D- <br />seam relative to the ground surface. <br />In this area the D-seam ranges from 3 to 11 feet in <br />thickness. Tire D-seam splits into an upper and lower seam <br />over most of the lease area. The Upper Coal Member is capped <br />by a thick sandstone, but the lenticular nature of <br />individual buc?s often hakes identification of the upp=r <br />contact difficult. The upuermost unit, tiie Barren member, <br />• <br />- 7 - <br />