BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 23, pp. 713-718, PLS. 42-43 DECEMBER 14, 1912 



TOYALAN^. AND LUCERO; THEIR STRUCTURE AND 



GENETIC RELATIONS TO OTHER PLATEAU 



PLAINS OF DESERTS ^ 



BY CHARLES R. KEYES 



{Presented hy title December 30, 1911) 



CONTENTS 



Page 



Dominant features of the plateau plain 713 



Structure of tbe plateau plain 714 



Toyalane 715 



Lava flows of the region 716 



Eolic character of the regional erosive activities 717 



Dominant Features of the Plateau Plain 



On the arid plains of the Southwest the two most striking features of 

 the landscape are the lofty isolated desert ranges and the lower trun- 

 cated hills which rise abruptly as walls above the general plains surface. 

 The first mentioned of these relief characters has long attracted wide 

 attention from travelers ; the second, notwithstanding the fact that it i^ 

 fully as impressive as the first, has scarcely received any notice at all. 

 R. T. Hill alone seems to have given them special consideration and a 

 name. For these plains above plains, or plains within plains, the term 

 plateau plains appears to be a very appropriate title. At the present 

 time particular interest attaches to the plateau plains because of the fact 

 that they seem to furnish the most direct and convincing testimony we 

 have of the defiative nature of general erosion under conditions of 

 aridity. 



In the dry regions plateau plains appear as even surfaces, more or less 

 well elevated above the general plains surface about. As broad, trun- 

 cated mounds they rise out of the vast expanse of level eartli after the 



1 Manuscript received by the Secretary of the Society March 25, 1012. 



(713) 



