22 LAKAMTE BASIN, WYOMING. 
SATANKA SHALE. 
The Satanka red shale lies between the Forelle limestone and the 
Casper formation in the Laramie region. ' It is named from Satanka 
siding, which is situated a short distance east of its outcrop zone. 
At the mouth of Gilmore Canyon its thickness is 232 feet, and the 
rock is sandy red shale with thin layers of soft red sandstone, all 
closely similar to much of the Chugwater formation. The Satanka 
shale outcrop is generally marked by a shallow valley at the foot of 
the long sandstone or limestone slopes of the mountains, with a low 
but distinct ridge of Forelle limestone on its west side. It outcrops 
almost continuously from T. 17 N. past Laramie and Red Buttes to 
Sportsman Lake, but on some of the divides it is covered by high 
terrace deposits and talus. The shale is absent in the Red Mountain 
region, where the Forelle. limestone lies directly on light-colored 
sandstones believed to be at the top of the Casper formation. It is 
possible, however, that these sandstones represent the Satanka shale. 
Local deposits of gypsum occur in the Satanka shale at Red 
Buttes. At the plaster mill 2 miles south of that place one bed is 
15 to 20 feet thick, and another 25 feet above is 10 feet thick. The 
upper bed was struck again half a mile farther north, near the Union 
Pacific Railroad. A 10-foot bed of gypsum was found in the upper 
part of the shales in a pit in sec. 2, T. 16 N., R. 73 W. 
No fossils were found in the Satanka shale, but its Pennsylvanian 
age is indicated by the occurrence of fossils of that series in the over- 
lying and underlying formations. 
TRIASSIC (?) SYSTEM. 
CHUGWATER FORMATION. 
Character and distribution. — Extending along the foot of the west 
slope of the Laramie Mountains there is a broad outcrop zone of red 
shales and soft red sandstones, which undoubtedly represent the 
Chugwater formation of other regions. The brilliant red color ren- 
ders the formation a conspicuous feature in many portions of the 
area. The outcrop passes through Laramie and extends southward 
past the north end of Boulder Ridge for some distance into Colorado. 
In the southern portion of the Laramie Basin the formation con- 
sists of the upper half of the u Red Beds" of former writers, but from 
Laramie northward it lies upon sandstones and limestones. It is 
extensively exhibited about Red Mountain, which takes its name 
from the prominent exposures on its north slope. Small areas 
appear in the faulted zone in Jelm Valley and along the southeast 
side of Sheep Mountain. It is well exhibited near Boswell's ranch 
on Laramie River, at the Colorado state line. Narrow zones of out- 
