REV88856

• Permit No: C1981019
• IBM Index Class Name: Revision
• Doc Date: 7/30/1992
• Doc Name: AFFIDAVIT OF PUBLICATION LEGAL NOTICE
• Type & Sequence: RN2
• Media Type: D
• Archive: No

Geology

Geologic information is found in Sections 2.04.5, 2.04.6, 2.05.2 and 2.05.3;
Maps 7 through 9A; and Exhibit 6 of the permit application. A generalized
geologic column for Colowyo is found in Figure 1 of this document.
The active mining site lies just west of the northward flowing Goodspring
Creek, which is paralleled by Colorado Highway 13. The area is a gently
sloping upland ranging from about 7,640 feet near the southwest corner to
6,560 feet near the northeast corner of the permit area. Valleys that cut
into the upland surface are generally narrow, V-shaped, and about 250 to 500
feet deep. North of the proposed active mine site, the topographic surface is
dominated by two ridges about two miles long, trending north-northeast,
bounded by Goodspring, Taylor and Wilson Creeks.
The permit area lies about six miles south of the axis of the Axial Basin
Anticline, a large northwest-trending fold found in the southern Uinta region
of the Piceance Basin. The anticline structure and corresponding syncline to
the south consist of thousands of feet of marine deposited sediments of
Cretaceous age.
To the south of the anticline, the axis of the Collum Syncline, a downward
fold, passes directly through the permit area, striking N 70 degrees W and
dipping from 0 to 20 degrees to the North. In the southeastern corner of the
permit area, near Streeter Fill, the Collum Syncline is influenced by the
Elkhorn Syncline and results in strata having an eastward dip and north-south
strike (see Map 7 and Figure 1 in the permit application).
There appears to be no evidence of faulting in the permit area; however,
linear features that may be fault-related have been observed from aerial
photographs. These lineations trend northwest with a strike approximately
north 70 degrees west, north 45 degrees west and north 30 degrees east, with a
near vertical inclination.
The coal bearing stratum of interest to the Colowyo operation are
stratigraphically located in the Mesa Verde Group within the Williams Fork
Formation of upper Cretaceous age. The Williams Fork consists of alternating
beds of sandstone, sandy shale, carbonaceous shale and coal. The coal section
to be mined is a 392-foot interval in the Fairfield Member of the Williams
Fork Formation. The quality of the coal seams is midway between bituminous
and sub-bituminous. These coal beds are underlain by 9,000 feet of Mesozoic
and 4,500 feet of Paleozoic sediments. The Williams Fork Formation is
estimated to be 1,600 feet thick in the permit area and is underlain by the
ridge-forming Trout Creek sandstone member of the Isles Formation.
Ten coal seams are mined in the Colowyo operation, "Y2," "Y3," "X ," "A2,"
"A3," "B1, "C," "D," "E" and "F." Four seams below the "F" cannot be mined
by surface mining methods. These seams are described in Northwest Colorado
Environmental Statement, Site-Specific Analysis. Overburden material consists
of a sequence of sedimentary claystones, siltstones, shales and carbonaceous-
silty shales. These sediments are typical of the cyclothems deposited along
the western interior of North America during Late Cretaceous time. The
site-specific stratigraphy is described in Exhibit 6 and on Map 8 of the
permit application.
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