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Most of the principal geologic structures in the Nucla Area have undergone a complex <br />tectonic history of recurring differential uplift, subsidence, deposition, erosion, folding, <br />and faulting beginning in early Pennsylvanian time and lasting to the present (Lohman, <br />1965). The largest of these structures is the 100 -mile long Uncompahgre Arch, a <br />northwest trending upwarp whose axis follows the crest of the Uncompahgre Plateau <br />roughly 10 to 15 miles directly north and northeast of the permit area. Other well <br />developed anticlines in the area include the Paradox Valley Complex, the Gypsum Valley <br />Anticline, and the Sinbad Valley Anticline. These anticlines, in contrast to the <br />metamorphic /igneous core complex found in the Uncompahgre Arch, have intrusive <br />cores of salt and gypsum derived from the Paradox Member of the Hermosa Formation. <br />Farther to the west in Utah, Tertiary laccoliths and stocks are evident in the LaSal <br />Mountains. <br />Lying between anticlines are several northwest trending synclines which contain the <br />greater part of coal reserves found in the region. Characteristically, these synclines are <br />shallow, broad, structurally simple folds with gently dipping flanks. The Nucla Syncline <br />is the largest of these structures occurring in the area and is approximately 65 miles long. <br />(see Map 2.04.5 -1 showing the axis of the syncline in relationship to the NHN permit <br />area. <br />A generalized geologic cross - section showing the mine's setting to adjacent structural <br />features is presented on Figures 2.04.5 -1. <br />In general, the present structural relief of anticlines and synclines found in the region is <br />due primarily to compressive and isostatic forces which produced folding in the late <br />Pennsylvania, late Cretaceous, Eocene and late Pliocene or early Pleistocene times <br />(Cater, 1970). All of the structures show various degrees of deformation along their outer <br />margins in the form of monoclines and high angle normal faults trending parallel or <br />subparallel to the direction of the axis. A major fault scarp of unknown displacement <br />marks the abrupt southwest edge of the Uncompahgre Uplift, and is shown on Figure <br />2.04.5 -1. Small folds and faults in Quaternary deposits on the crests of the salt anticlines <br />may indicate that structural readjustments are still occurring (Cater, 1970). <br />The stratigraphy of the general permit area is simple. The Dakota Formation of lower <br />Cretaceous covers most of the surface in the area, (see Map 2.04.5 -1). However, in <br />deeper canyons to the east along the lower reaches of Tuttle Draw, Coal Canyon and the <br />San Miguel River, Morrison Formation and older strata are exposed. <br />This section has briefly described the regional geology of the NHN Mine permit area as <br />an introduction to the section on site specific geology presented in Section 2.04.6 of the <br />permit application. <br />Section 2.04.5 Page 2 April2011 <br />