RED MOUNTAIN, ARIZONA 



141 



H.S 

 CO. 

 CO. 

 CH4 

 H3 . 



8.90 



62.62 



14.46 



1.30 



7.01 



5-71 



The structure. — The San Francisco Mountains and associated 

 cones rest on the Colorado plateau, where Carboniferous limestones 



Fig. 2. — General view of Red Mountain from the northeast. 



appear at the surface." According to Dutton, the plateau was not 

 reduced to the Carboniferous horizon until late in Miocene times. ^ 

 The writer has reported evidence of Pleistocene glaciation in the 

 main crater of the San Francisco Mountain, ^ and it is fair to assume 

 that volcanic activities had ceased in the entire region by that time. 

 The geologic age of these mountains is therefore probably late Ter- 

 tiary. The cone under consideration appears to rest, in part at 

 least, upon a lava flow that issued from the main crater or from 



2 Button, Tertiary History of the Grand Canyon District, Monograph II, U. S. 

 Geological Survey, p. 221. 



3 "Glaciation of San Francisco Mountain, Arizona," Journal of Geology, Vol. 

 XIII (1905), p. 276. 



