2009-01-14_PERMIT FILE - C1996083A ‎(2)‎

• Permit No: C1996083A
• IBM Index Class Name: Permit File
• Doc Date: 1/14/2009
• Section_Exhibit Name: 2.04 Information on Environmental Resources
• Media Type: D
• Archive: Yes

•
2.04.6 Geology Description.
(1) No response required.
(2)(a) Not applicable.
(3)(a) The North Fork Valley of the Gunnison River is located near the western margin of the
Colorado portion of the central Rocky Mountain system. The permit and adjacent areas
are situated on the southern flank of the Piceance Creek structural and sedimentary
basin. The area is bounded by Larimide structural and physiographic features on the
following sides: West Elk and Elk Mountains on the east; Gunnison Uplift on the south;
Uncompahgre Uplift on the west-southwest; and Grand Mesa-Piceance Basin on the
north (Collins, 1976).
Generally, Paleozoic strata comprise the Elk Mountains on the East; Mesozoic
and Cenozoic strata area exposed within the Uncompahgre Uplift, pre-Cambrian
within the Gunnison Uplift, and Mesozoic Strata comprise the immediate North
Fork Valley. The area is further modified by Tertiary intrusive porphyritic rocks,
which are predominantly laccolithic in structure (West Elk Mountains, Hai1,1972)
and Miocene basalt flows capping Grand Mesa (lunge, 1978).
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Stratiaraohv: The stratigraphy of Cretaceous coals has been addressed by
numerous authors since the early 1900's. During the close of the Jurassic
System, the present Rocky Mountain area was inundated by the Cretaceous
Ephric Seaway, which extended from Canada to Mexico (Weimer, 1976). The
basal transgressive rock unit deposited at this interval was the Dakota sandstone
(lower Cretaceous). As the basin developed, 2,000 - 5,000 ft. (or greater) of
marine sediments were deposited and are preserved as the Mancos shale.
The Mesaverde Formation of Holmes, (1877) has been extended throughout
western Colorado, eastern Utah, and southwestern Wyoming, and represents
a dominantly regressive sequence which formed in response to larger detrital
input from the Cordilleran region to the west, than contemporaneous basin
subsidence (Weimer, 1976). The Rollins Sandstone Member (Lee, 1912) of the
Mesaverde Formation represents the basal regression of the Cretaceous
Seaway, although Collins (1976) identified seven cycles of marine-nonmarine
deposition in the Eastern Piceance Basin. The coal deposits of the area were
deposited as the complex relationships of deltaic, fluvial, and barrier island facies
were intermittently modified bytransgressive-regressive cycles of the retreating
Cretaceous shoreline.
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