380 W. C. KNIGHT — JURASSIC KOCKS OF SOUTHEASTERN WYOMING 



is the E^utton* anticline, which is a spur-like projection from the Lar- 

 amie mountains, extending northwest. At Alcova, a postoftice on the 

 North Platte river below the month of the Sweetwater, is the Fremont f 

 fault, which is very extensive and is the source of the Hot springs at that 

 point. In the northeastern corner of the area is the Sioux J fault, where 

 the .In lassie rocks have been elevated until on a level with the Miocene 

 Tertiary. At Red mountain, at the southern end of the Laramie plains, 

 the Red Mountain fault has disturbed the Jurassic. 



Distribution of Jurassic Rocks 



The distribution of the Jurassic rocks conforms very closely to the 

 disturbances just described. They occur in narrow bands flanking the 

 mountain ranges, encircling the anticlinal folds, and as isolated areas 

 along faults. In some instances the Miocene rocks have entirely ob- 

 scured many miles of the older sedimentaries flanking the ranges. On 

 the eastern slope of the Laramie mountains from the Colorado line as 

 far north as Horseshoe creek the Miocene originally covered nearly all 

 of Mesozoic and Paleozoic strata. 



Jurassic rocks are not known within the above limits, but may be 

 found in some of the valleys which have suffered great denudation, as 

 Horse creek and Chugwater creek. Triassic sandstones are exposed in 

 these valleys at the foot of the mountains. From Horseshoe creek the 

 Jurassic bands can be traced along the northern flank of the Laramie 

 mountains to the Platte river to a point 8 or 10 miles west of Casper, 

 and in all probability there are some exposures paralleling this range 

 north of Laramie peak which have been caused by a slight secondary 

 fold. Along the western slope of the Laramie mountains the Jurassic 

 bands extend north and northwest to a point a few miles beyond Sheep 

 creek, where they disappear beneath the Tertiary. Likewise, after fol- 

 lowing the irregular outline of the eastern and northern slopes of the 

 Medicine Bow mountains, this series disappears several miles southwest 

 of Elk mountain beneath more recent formations. They are likewise 

 buried on the north side of the Shirley mountains, and the exposures 

 near the Fremont and Sioux faults disappear in both directions beneath 

 the Miocene. The remaining exposures are to some extent covered with, 

 debris and soil, but are often seen rising in the abrupt bluffs with steep 

 slopes and capped with Dakota sandstone and conglomerate. Within 

 this area there are not less than 450- linear miles of exposure. 



* Named from Hutton lakes, which are in this vicinity. 



\ Named in honor of Fremont, who first described the hot springs flowing from this fault. 



J Named after the Sioux nation. 



