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State Reg. <br />less than 5,672 feet (MSL) in the southeast part along Tuttle <br />Draw (see Exhibit 7-1). Total topographic relief for the per- <br />mit area is 95 feet (MSL). <br />Topographic features on the permit include gentle southwest <br />facing slopes, low rolling hills, old spoil piles, regraded <br />mined areas cut by open pits, and shallaa drains (euphemeral) <br />which feed Tuttle Draw (intermittent). <br />II. REGIONAL GEOLOGY <br />A. INTRODUCTION. Southwest Colorado exhibits a wide and unu- <br />sual variety of physiography, mineral resources, soils, ground- <br />water conditions, and surface water conditions which are, to a <br />great extent, influenced by the region's geology. In this part <br />of the San Juan Coal P.egion (Nucla-Naturita Coal Field), a <br />series of major northwest trending structural features and cocn- <br />• plex intraformational stratigraphic relationships control the <br />overall occurrence and quality of coal reserves. This section <br />will briefly describe the regional geology of the Nucla Area as <br />an introduction to the section on site specific geology pre- <br />sented later in this section of the permit application. <br />B. STRUCTURE. Most of the principal structures in the Nucla <br />Area have undergone a ca~lex tectonic history of recurring dif- <br />ferential uplift, subsidence, deposition, erosion, folding, and <br />faulting beginning in early Pennsylvanian time and lasting to <br />the present (Lohman, 1965). The largest of these structures is <br />the 100-mile long Uncompahgre Arch, a northwest trending upwarp <br />whose axis folloias the crest of the Uncompahgre Plateau roughly <br />10 to 15 miles directly north and northeast of the mine site <br />(see ~hibit 6-2). Other well developed anticlines in the area <br />include the Paradox Valley Coamlex, the Gypsum Valley Anticline, <br />and the Sinbad Valley Anticline. These anticlines, in contrast <br />L <br />6-2 <br />