STRATIGRAPHY. 23 
crop of the steeply dipping beds appear on either side of the Cen- 
tennial Valley, extending northward to the fault which cuts off all 
the formations at the north end of that valley. The formation is 
brought to the surface by the anticlines north and east of Medi- 
cine Bow and Rock Creek, covering considerable areas in a broad 
belt extending from the foot of Como Bluff eastward past Boswell 
Spring and also in the slopes of Flat Top Ridge. It is exposed in 
the Freezeout uplift and in wide outcrops on and near Sheep Creek 
in the vicinity of the mouth of Mule Creek. Three miles southeast 
of Arlington reddish shales outcrop in the south end of a foothill of 
the Medicine Bow Mountains, but the exposure is so small that it 
could not be determined whether the beds were Chugwater or Casper. 
In the upper portions of the valleys of Little Medicine Bow and Bone 
creeks the formation is buried under Tertiary deposits, and in the 
vicinity of Laramie it is extensively hidden by Quaternary sands 
and gravels. 
Local features. — The formation consists mostly of red shales and 
fine-grained red sandstones, with a subordinate amount of lighter 
colored sandstones, thin beds of limestone, and deposits of gypsum. 
The gypsum beds are especially thick and prominent in the Red 
Mountain neighborhood. The fine-grained massive sandstones 
weather with rounded outlines, especially where the beds are hori- 
zontal, and in places they rise in monuments, one of which near 
Steamboat Lake has suggested the name of that body of water. 
(See PI. V, B.) In many other localities where the beds dip steeply 
the outcrop of the sandstones presents ragged ledges of considerable 
prominence. In the southern portion of the Laramie Basin the 
formation is so largely covered by the Quaternary deposits that 
complete sections are rare, but one exposed in the north face of Red 
Mountain is believed to comprise all the beds lying between the 
fossiliferous limestone (Forelle) underlying the gypsum and the base 
of the typical Morrison. 
Section of Chugwater and overlying beds in Red Mountain, Wyoming. 
Morrison: Feet. 
Shale with green nodules 28 
Limestone 1 f ] 
Bine shale [Morrison fossils 
Limestone J 
Blue shale 
Chugwater: 
Light sandstone 
>n 
L2 
Terra-cotta to blue shale 20 
Soft sandstone or sandy shale 10 
Terra-cotta shale 17 
Light-buff soft massive sandstone 30 
Terra-cotta, blue, and green shales 65 
