iyo 



PROCEEDINGS OF THE CHICAGO MEETING 



Figure 3. — Face of lotver Ledge of Niagara Escarpment 

 The rounded and grooved edge is produced by the glacier moving across it. 



PENEPLAINAL AFFINITIES OF HIGH PLATEAUX OF UTAH 

 BY CHARLES E. KEYES 



iAl)stract) 



Prodigious outpourings of lavas over tlie Cordilleran region of western 

 America during Tertiary times give origin at later date to curious landscape 

 idiosyncrasies. PhysiograpMcally, mesa land is almost unique. Nowhere else 

 on the face of the glohe are there so many planation levels persisting in such 

 close juxtaposition. Nowhere else are so many distinct plains presented one 

 above another through a mile of air above the present general plains surface, 

 or in old sediments through a space of several miles below the same surface. 

 Nowhere else are climatic conditions so favorable for general plains genesis. 

 From the very beginning of each geographic cycle, plain is the characteristic 

 and dominant landscape type. Plateau plain of the desert is the reminiscent 

 record of intracycle planation such as is preserved in no other attainment to 

 baselevel. 



Of the four great peneplains which spread over the ancestral Rockies since 

 the close of Paleozoic times, the Mid-Tertiary or Miocene savanna seems to 

 be represented in the last lingering traces by the summital flats of the high 

 plateaux. When these few all but vanquished remnants, the high plateaux of 

 Utah and the Mesa de Maya of the eastern side of the Cordillera, finally 

 wither away, as they will shortly, no positive evidences of this once vast 

 peneplain remain. In the high plateaux of Utah lies also the key to the genesis 

 and structure of the Great Basin ranges. 



Presented by title in the absence of the author. 



