THE LATER CENOZOIC HISTORY OF THE WIND RIVER 
MOUNTAINS, WYOMING 
LEWIS G. WESTGATE anp E. B. BRANSON 
INTRODUCTION 
The Wind River Mountains of West Central Wyoming run 
from Union Pass on the north, for over one hundred miles southeast 
to the Sweetwater River near Atlantic City. The range rises from 
the plains level of 5,000 to 6,000 feet on the east, to a crest line 
which in a number of places stands over 13,000 feet above the sea. 
Wind River Peak is 13,500, and Gannett Peak, the highest summit 
in the range, 13,785 feet above the sea. 
The continental divide follows the crest of the range. On the 
east the drainage is by the Wind River and Platte and its tributaries 
to the Missouri and the Atlantic. Along the west side, except at 
the south end where the drainage is by the Sweetwater to the North 
Platte and the Atlantic, the streams are tributary to the Green 
River, thence following the Colorado to the Pacific. 
Geologically the structure of the range is similar to that of the 
Big Horns and the Black Hills, and consists of a central axis of 
crystalline rocks, circled by belts of upturned Paleozoic and Meso- 
zoic rocks, beyond which lie the nearly level Tertiaries. Along 
most of the east side of the range the conditions in the Black Hills 
are exactly reproduced, but along much of the south and west sides 
the Tertiaries overlap the Paleozoics and rest directly against the 
crystallines. Where all the formations are present each plays a 
distinctive part in the topography. ‘The crystalline rocks form the 
central part of the range. The Paleozoics form the main foothills 
and slopes up to 9,000 or 10,000 feet, while the Mesozoics and 
Cenozoics underlie the plains. The lowest Mesozoic and highest 
Paleozoic, the Chugwater Red Beds, which are mainly sandstone, 
often make prominent ridges, rising 1,000 to 1,500 feet above the 
neighboring valleys, facing the range, and sometimes separated 
from it by a conspicuous red valley, worked out on the softer 
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