UTAH PENEPLAINS 
123 
Peneplains of the eastern Rocky Mountain belt give clue to what 
should be expected in the west. Since the great thick limestone 
plate which now surmounts the southern Rocky Mountain region 
was laid down in the shallow waters of epicontinental seas in Mid 
Carbonic times it appears to have undergone no less than five 
notable orographic wrappings. Of these upraisings the first oc¬ 
curs in Late Carbonic time, outlining the ancestral Rocky Moun¬ 
tains. The second period of regional upheaval is ascribed to Late 
Cretacic time. A third movement of positive diastrophic char¬ 
acter takes place in the Mid Tertic period; and a fourth occurs in 
Late Tertic times. The fifth uprising appears to be in progress 
at the present time and to be acting about as fast as mountain 
genesis ever goes on. 
Each orographic movement appears to have been followed by 
long-continued regional planation. Five such major planation 
surfaces are still well preserved. So widely scattered are the 
evidences in the cases of three of these levelings, and so near ex¬ 
tinguishment are some of these old base-levels that their correla¬ 
tion and adjustment with present features are attended by many 
difficulties. Only by careful consideration of the sequence of 
geological events does it seem possible to connect the known 
remnants of each peneplain and to correlate the several plains- 
surfaces. 
The larger relations of the different peneplains, as they bow over 
the Cordilleran tract, are indicated in the annexed diagram (fig¬ 
ure 11) : 
