176 Adventures in Scenery 



ing the Pliocene epoch (late Tertiary) there followed a lengthy 

 interval of quiet. The waters on the lava-covered parts of the 

 range established new courses, and cut canyons some of which 

 reached depths of 1,000 feet or more. Vegetation established 

 itself, and forests of Sequoias, ancestors of the big trees of the 

 present time, flourished throughout the region. 



Final Uplift of Sierra Range a 

 Late Geologic Event 



At the beginning of Quaternary time about 1,000,000 

 years ago commenced those great upheavals and tilting move- 

 ments that gave to the Sierra Nevada its present great altitude. 

 The summit peaks were raised to almost double their previous 

 height, Mount Lyell being lifted to more than 13,000 feet above 

 sea level. At the same time fracturing and faulting occurred 

 on an enormous scale. Owens Valley and other desert regions 

 adjoining the range on the east and south were depressed, and 

 so the Sierra Nevada came to stand out in its present imposing 

 form, with gentle westward slope, sharply defined crest, and 

 abrupt eastward-facing escarpment. 



After the grand climax of mountain-building movements 

 that ushered in the Quaternary period earth stresses abated in 

 intensity. Upheaval and down-faulting occurred less fre- 

 quently, and the Sierra Nevada has suffered no marked further 

 changes in height or in general form. Minor movements, how- 

 ever, have continued to occur at intervals into historically 

 recent times. 



One notable dislocation has taken place at the eastern base 

 of the Sierra Nevada within historic time. It gave rise to the 

 famous Owens Valley earthquake of March 26, 1872. The 

 fault scarps produced by this earth movement are still con- 

 spicuous, and are easily traced for distances of several miles. 

 They vary from 8 to 2 5 feet in height. The tremors produced 

 by this earth movement were so strong that even in the Yosem- 

 ite Valley, more than a hundred miles away, great avalanches 



