POST-CRETACEOUS HISTORY OF WESTERN WYOMING 115 



here for the making of the high peneplain and the subsequent 

 sculpturing of the modern topography before the last stage of 

 glaciation. Since we cannot yet translate physiographic results 

 into years or even into geologic periods, the portion of the Tertiary 

 and Quaternary periods to be allowed for these events cannot be 

 estimated with any degree of confidence. From the evidence 

 within the district, then, it is justifiable to conclude only that the 

 deformation probably followed the early Oligocene and preceded the 

 Pleistocene. 



From a general study of the tectonic disturbances at various 

 times in the earth's history, such as the Appalachian revolution, the 



Fall 



Fig. 10 



late Jurassic orogeny of the Pacific, and many others, it seems to be 

 established as a general rule that deformative movements are 

 roughly periodic and that they affect long belts which are con- 

 tinental or even world-wide in their dimensions. It seems fairly 

 safe to assume that the deformative movements evidenced in west- 

 ern Wyoming accorded with this principle, and were manifestations 

 of a much more widespread disturbance, the effects of which should 

 be recognized in adjacent states. It is also self-evident that any 

 such widespread disturbance would cause notable changes in the 

 relief of the land, and would revolutionize the physiographic 

 activities of the region so affected. These changes should now be 

 found in the unconformities or in sudden changes in the character of 

 sediments. 



In the Coast Ranges of California, Arnold and others appear to 

 have shown beyond reasonable doubt that sedimentation prevailed 



