2012-06-20_PERMIT FILE - C2010089A (9)

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