STRUCTURE. 53 
to the Chugwater. The latter extends down to Little Medicine Bow 
Creek and partly up the north slope. Higher on this slope the center 
of the uplift presents the top sandstone of the Casper formation. 
On the north side of this ridge are exposed red beds dipping to 
the north and cut off by a fault, along which Niobrara beds appear 
near the road and the upper sandstone of the Benton farther west. 
These beds descend into a syncline holding the Montana group which 
extends to the Freezeout uplift on the northwest and far up the valley 
of Muddy Creek on the north and northeast. The fault dies out 
within a short distance to the east and a symmetrical anticline 
extends up the divide between Bone and Sheep creeks. The dips are 
all gentle. This anticline exposes Chugwater red beds as far east as 
the east line of R. 77 W., beyond which there is a downward pitch 
and the outcrops curve over the flexure. In crossing the axis of 
the flexure the Cloverly formation rises into a prominent butte in 
the west side of T. 24 N., R. 76 W. Farther east the flexure is lost 
in Benton shales mostly covered by Tertiary beds. 
FREEZEOUT UPLIFT. 
Only the east end of the Freezeout Hills extends into the area 
shown on the map (PI. I). It presents the structural relations shown 
in the left-hand ends of sections 1 and 2, Plate VIII. The structure 
is that of a half dome, with sides dipping to the east, north, and south. 
The Chugwater red beds are prominent to the west and are bordered 
by semicircular outcrops of a succession of formations from Sundance 
to lower Montana. The Cloverly formation rises in a prominent 
ridge of which the outer slopes descend to the outcrops of the Benton. 
A mile or more distant is the Niobrara, partly covered by old terrace 
deposits, and then the shales of the Montana, which extend up the 
valley of Muddy Creek and constitute the low ridge between that 
stream and Little Medicine Bow Creek. Farther north, in T. 26 N., 
R. 78 W., the pitch to northwest so deepens the basin that it holds 
the sandstone of the Montana. 
MINERAL RESOURCES. 
COAL. 
Associated with the sandstones of the upper part of the Montana 
are coal beds ranging in thickness from a few inches to 6 feet or more 
and occurring at several horizons. The beds appear not to be con- 
tinuous for long distances and vary greatly in thickness. They are 
exposed at few points; consequently their extent and relations can 
not be determined. 
One of the first mines in Wyoming was opened by the stage com- 
pany in 1865, near the old overland trail crossing of Rock Crock. 
The coal was used for blacksmithing. 
