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State Reg. <br /> to the metamorphic/igneous core complex found in the Uncompahgre <br /> Arch, have intrusive cores of salt and gypsum derived from the <br /> Paradox Member of the Hermosa Formation. Far to the west in <br /> Utah, Tertiary laccoliths and stocks are evident in the LaSal <br /> Mountains. <br /> Lying between anticlines are several northwest trending syn- <br /> clines which contain the greater part of coal reserves found <br /> in the region. Characteristically, these synclines are shallow, <br /> broad, structurally simple folds with gently dipping flanks. <br /> The Nucla Syncline (San Miguel Syncline) , as shown in Exhibit <br /> 6-1, is the largest of these structures occurring in the area. <br /> It is approximately 65 miles long. <br /> Geologic maps showing outcrop and structural relationships of <br /> the area are presented in Exhibits 6-1 and 6-2. Structure con- <br /> tours drawn on the base of the Dakota Sandstone are illustrated <br /> in Exhibit 6-2. A generalized geologic cross-section showing <br /> the mire's setting to adjacent structural features is presented <br /> in Figure 6-1. <br /> In general, the present structural relief of anticlines and sny- <br /> clines found in the region is due primarily to compressive and <br /> isostatic forces which produced folding in the late Pennsylvania, <br /> late Cretaceous, Eocene and late Pliocene or early Pleistocene <br /> times (.Cater, 1970) . All of the structures show various de- <br /> grees of deformation along their outer margins in the form of <br /> mcnoclines and high angle faults trending parallel or subparal- <br /> lel to the direction of the axis. A major fault scarp of un- <br /> known displacement marks the abrupt soutwest edge of the <br /> Uncompahgre Uplift, and is shown in Figure 6-1. Small folds <br /> and faults in Quaternary deposits on the crest and salt anti- <br /> clines may indicate that structural readjustments are still <br /> occurring (Cater, 1955) . <br /> 6-3 <br />