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• 2.04.6 Geology Description. <br />(1) No response required. <br />(2)(a) Not applicable. <br />(3)(a) The North Fork Valley of the Gunnison River is located <br />near the western margin of the Colorado portion of the <br />central Rocky Mountain system. The permit and adjacent <br />areas are situated on the southern flank of the Piceance <br />Creek structural and sedimentary basin. The area is <br />bounded by Larimide structural and physiographic features <br />on the following sides: West Elk and Elk Mountains on the <br />east; Gunnison Uplift on the south; Uncompahgre Uplift on <br />the west-southwest; and Grand Mesa-Piceance Basin on the <br />north (Collins, 1976). <br />Generally, Paleozoic strata comprise the Elk Mountains on <br />the East; Mesozoic and Cenozoic strata area exposed <br />within the Uncompahgre Uplift, pre-Cambrian within the <br />Gunnison Uplift, and Mesozoic Strata comprise the <br />immediate North Fork Valley. The area is further <br />• modified by Tertiary intrusive porphyritic rocks, which <br />are predominantly laccolithic in structure (West Elk <br />Mountains, Hail, 1972) and Miocene basalt flows capping <br />Grand Mesa (lunge, 1978). <br />Stratiaraohv: The stratigraphy of Cretaceous coals has <br />been addressed by numerous authors since the early <br />1900'x. During the close of the Jurassic System, the <br />present Rocky Mountain area was inundated by the <br />Cretaceous Ephric Seaway, which extended from Canada to <br />Mexico (Weimer, 1976). The basal transgressive rock unit <br />deposited at this interval was the Dakota sandstone <br />(lower Cretaceous). As the basin developed, 2,000 - <br />5,000 ft. (or greater) of marine sediments were deposited <br />and are preserved as the Mancos shale. <br />The Mesaverde Formation of Holmes, (1877) has been <br />extended throughout western Colorado, eastern Utah, and <br />southwestern Wyoming, and represents a dominantly <br />regressive sequence which formed in response to larger <br />detrital input from the Cordilleran region to the west, <br />P6PMIT APPLIGTIOP <br />2-04 - 11 - <br />