TOPOGRAPHY OF CENTRAL WYOMING 



rocks. In some localities as on the rim of Bates Hole, complex 

 bad-land topography is found in the soft Tertiary rocks in 

 close association with the simple and smooth topography of 

 the harder Mesozoic rocks. 



The present surface of the plains as a whole is discordant 

 with the underlying rock structure, that is the surface of the 

 plains does not agree with the dip of the rocks but rather bevels 

 off the dip. This feature indicates, beyond question, that the 

 region has been base-leveled. 



Inasmuch as the Tertiaries are unconformable with the 

 Cretaceous rocks and are laid down upon these inclined Meso- 

 zoics in a horizontal position, it would appear that the base 

 leveling must have been post-Cretaceous. 



The plains are covered by a thin, but effectual, layer of 

 gravel, which is largely siliceous in character, and largely local 

 in origin, as similar types are abundantly found in the still un- 

 weathered rocks. 



This is especially well shown in the neighborhood of the 

 Fox Hills formation, where the great nodules, which character- 

 ize that formation, are found scattered about the surface of 

 the ground, left behind in the decay of the rocks. As the 

 mountains are approached, the character of the gravel changes, 

 there is a great accession of rocks which form the mass of the 

 mountains themselves; in such cases the gravel is of drift origin 

 in whole or m part. 



Terraces-. The terraces are another of the important 

 topographic features of the region. The streams in most 

 instances are bordered by them, In many instances, as at 

 Cooper's Creek, there are three terraces lining the stream. They 

 are usually broad and reach heights of from fifty to one hundred 

 feet. The valleys in which these terraces are found are also 



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