2025-04-09_PERMIT FILE - C1981019A ‎(3)‎

• Permit No: C1981019A
• IBM Index Class Name: Permit File
• Doc Date: 4/9/2025
• Section_Exhibit Name: 2.04 Information on Environmental Resources
• Media Type: D
• Archive: Yes

RULE 2 PERMITS
forming unit in the Danforth Hills, has been called the "White Rock" because of its characteristic
exposures.
The deposition of the Trout Creek Sandstone marked a major regression of the Late Cretaceous
seaway over a large region.
The resulting clean, well sorted blanket sand formed by this migrating beach and barrier island
complex is an aquifer of regional extent in Northwest Colorado. Under the area to be mined within
the Colowyo Permit area,the Trout Creek sandstone underlies the lowest surface recoverable seam
to be mined by 800 feet. Considering the nature of the intervening strata which is comprised of
primarily claystone, shales, and siltstones; it is very doubtful the Colowyo operation will impact
the Trout Creek sandstone.
The Iles Formation in the permit area is estimated to be 1,375 feet thick. The Iles Formation forms
most of the cliffs that surround the Axial Basin. The Iles Formation lies approximately 1,700 feet
beneath the actual mining area; however, minor folds or faults in the regional trend bring the
formation nearer the surface.
Williams Fork Formation-The Williams Fork Formation consists of alternating beds of sandstone,
sandy shale and coal. It is distinguished from the Iles Formation by its thick zones of brick red
sandstone and shale, which have been colored from adjacent naturally-burning coal beds, a
common occurrence in the Axial area. The coal beds in the formation are uniformly distributed in
the vicinity of the mine but generally vary greatly within the regional extent of the unit. The
stratigraphic thickness of the Williams Fork Formation in the permit area has been estimated to be
about 1,600 feet;its degree of areal extent in the Axial Basin is similar to that of the Iles Formation.
The Williams Fork Formation is the predominant coal-bearing formation in the Mesa Verde
Group. Mesa Verde coals associated with the Fairfield Group, the coal-bearing zone above the
Trout Creek Sandstone, rank in quality about midway between bituminous and sub-bituminous.
Although the Twenty Mile Sandstone Member is a regional aquifer noted within the Williams Fork
Formation in the Craig, Hayden and Steamboat Springs area, a facies change within the Williams
Fork Formation has eliminated the Twenty Mile Sandstone in the Danforth Hills Area.
Structure
The area around the mine is dominated by the Axial Basin Uplift, an anticline, or arch, which is a
southeastward extension of the larger Uinta Mountain Arch. The Axial Basin anticline is an
asymmetrical fold, the axis of which trends north 60° west, with strata dipping(inclining) steeper
on the south side of the axis than on the north. The south flank of the anticline has several
secondary folds trending subparallel and at approximate right angles to the main anticlinal axis. In
general,the rocks of the broad anticline have not been stressed sufficiently to cause them to break
severely, but a few discontinuous normal faults trending primarily parallel to the anticlinal axis
are found in the area.
The structure of the permit area is geologically simple. The axis of the Collom syncline, a
downward fold, passes through the permit area as shown on the Geology Map (Map 7). Bedding
orientation,as measured on surface outcrops,generally has a strike of N 70°W and is characterized
Rule 2 Permits 2.04-9 Revision Date: 12/20/19
Revision No.: TR-135