314 (1E0L0GY. 



" What kind of a mountain it was at that time, how high, and what its con- 

 figuration, we know not; for the continuous erosion of the Cretaceous and Ter- 

 tiary times had nearly swept it clean away. The cycle of its mountain life had 

 reached its last stages. By continuous erosion it had been reduced to a pene- 

 plain, with its wide-sweeping curves of broad shallow channels and low-rounded 

 divides. The rivers had reached their base-levels and rested. This was the 

 work of the Cretaceous and Tertiary. 



" Then came the post-Tertiary rejuvenation of the mountain life, by the 

 formation of a fissure on the eastern slope, the heaving of the whole mountain 

 block on its eastern side with a great eastern fault scarp; the transference of 



Fig. 463. — Represents the outline of the Point of Rocks formation of the last section, 

 as it would have appeared without erosion, after faulting. The length of the sec- 

 tion is about 57 miles. The vertical scale is the same as the horizontal. The 

 displacement at P is nearly 20,000 feet. (After Powell.) 



the crest to the extreme margin with great increase of the western slope and 

 consequent revival of the erosive energy of the rivers. Coincident with this 

 in middle California there was a great outpouring of lava, which ran in streams 

 down the western slope, filling up the old river-beds, and displacing the rivers. 

 The displaced rivers, with recently and fiercely aroused energy, immediately 

 commenced cutting new channels, which are now 3000 to 6000 feet deep, and 

 far below the old; so that these latter are left with their lava-covered gravels 

 high up on the present divides. This was the work of the Ozarkian." ' 



Not only the deep canyons, but all the scenery of the high Sierras 

 is post -Tertiary. " Its bold, rugged, savage grandeur is due to its 

 extreme recency. The wildness of youth has not been tempered and 

 mellowed by age." 2 It should be added that the beginning of the 

 re-elevation of the Sierras, after peneplanation, is usually placed in 

 late Miocene time. 



Near the Pacific coast, too, notable changes marked the closing 

 stages of the Pliocene and the transition from it to the Pleistocene. 

 In some parts of southern California (Fort Frazer, Los Angeles County) 

 marine Pliocene beds are said to occur up to altitudes of 6000 feet, 3 

 and in others (San Luis Obispo), there was folding (Fig. 444) and fault- 

 ing at the close of the Pliocene, while the shore-line was pushed out 



1 LeConte, Jour. Geol., Vol. VII, p. 529-530. 



2 Le Conte, loc. cit., p. 530. 



3 Ilershey, Am. Geol., Vol. 29, p. 364. 



