THE PLEISTOCENE OR GLACIAL PERIOD. 



335 



where an altitude of nearly 12,000 feet was necessary to give origin to them. 

 There were also small glaciers on the northeast slope of the San Francisco moun- 



Fig. 471 . — Map showing the areas of the glaciers (black areas) of the Bighorn moun- 

 tains during the last important glacial epoch. (Blackwelder and Bastin.) 



tain of Arizona (nearly 13,000 feet, lat, 35° 21'), the most southerly point where 

 glaciers are known to have existed in the United States. 1 



x Atwood, Jour, of Geol., Vol. XIII, p. 276. 



