PERMFILE114933

• Permit No: C1985070
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: 2.04 Environmental Resources
• Media Type: D
• Archive: No

2.04.6 Geology Description
•
Structure
The Mt. Harris Coal Company is located along the Yampa River at an
elevation of about 6,400 feet. The loadout site is situated in the sand
wash structural basin of northern Colorado. The most notable structure
in the immediate area is the Tow Creek anticline. The entire area
including the Tow Creek anticline is heavily faulted. The geology of
the area is shown on Figure 2, Geology of the Mt. Harris Area.
Stratigraphy
The exposed rock sequence in the region consists primarily of at~out
13,500 feet of Late Cretaceous, Tertiary, and Quaternary age sedimentary
deposits. Some intrusive and extrusive igneous rocks that are probably
Miocene in age occur regionally. The largest regional occurrence of
• extrusive rocks occurs in the Flattop Mountains about 25 miles south of
the Mt. Harris permit area.
The oldest rock formation outcropping in the region is the Mancos shale
of Late Cretaceous age. The Mancos shale is about 5,000 feet thick and
is conformable with the overlying Mesaverde group and the underlying
Dakota sandstone. The Mancos shale is predominantly a dark-gray marine
shale with interbedded layers of sandstone near the top and interbedded
layers of sandstone and limestone near the base. There is a sandstone
layer about 50 feet in thickness situated approximately 300 feet above
the base of the formation which is thought to be equivalent to part of
the Frontier sandstone. Above the Mancos Shale lies the Mesaverde Group
also of late Cretaceous age. This group consists of two formations, the
oldest being the Iles Formation and the youngest being the Williams Fork
Formation. Together these two formations represent about 3,000 to 3,500
feet of sandstone interbedded with shales, sandy shales, and coal.
The general geologic sequence of the area is shown on Figure 3, Geologic
• Section.
2.04.6-1