CENOZOIC HISTORY OF THE LARAMIE REGION, 
WYOMING? 
ELIOT BLACKWELDER 
University of Wisconsin, Madison, Wis. 
The region described in this paper centers in the city of Laramie 
in southeastern Wyoming. It is situated in the eastern edge of the 
Rocky Mountain province. Much has been written about its stratig- 
raphy and structure, but less of its physiographic features and 
their origin. The latter I purpose to describe and interpret here, 
with such help as is afforded by the contemporaneous deposits. Some 
of the questions which arise may be decided even now with reasonable 
confidence, but others require the further study which will be given 
them in later years. Even on these doubtful points suggestions may 
be of value to those who pursue the future work. 
Bed-rock geology—The fundamental rocks of the district are 
granites, gneisses, and schists of pre-Cambrian age. Upon their 
deeply eroded surface rests a thick succession of unaltered sedimen- 
tary rocks which range from Pennsylvanian to late Cretaceous. 
Although some unconformities divide this series, it appears nevertheless 
to be a unit, structurally. Under the plains the strata are nearly flat. 
In the mountains they have been arched in unison and are now found 
dipping away at various angles from the axes of the anticlines. From 
the physiographic point of view the sedimentary sequence may be 
divided into two parts: the Carboniferous limestone and the younger 
beds chiefly of Permian and Mesozoic age. The limestone is the 
most resistant terrane of the district and its outcrops are usually 
marked by “hog-back” ridges. The shales and weak sandstones 
of the other divisions are exposed in the lowlands bordering the 
mountains. 
Upon the eroded edges of the tilted Mesozoic and older rocks lies 
a third group of strata—the Tertiary and Pleistocene sediments. 
They are nearly horizontal and largely unconsolidated. 
1 Published by permission of Director, U. S. Geological Survey. 
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