The Sierra Nevada Range 165 



What manner of mountain range is the Sierra Nevada? 

 The present range is the latest in a series of mountain ranges 

 that have existed where the Sierra Nevada now is. Mountains 

 are popularly thought of as fixed features of the world land- 

 scape. "As old as the hills" is a common expression. As young 

 as youth would probably be more nearly correct. The Sierra 

 Nevada range is young only probably about a million years 

 old. The crest of the High Sierra remains today much as it 

 was in the "beginning." Its "beginning" was after other great 

 mountain systems had come and gone in the same locality. 



The mountain systems that previously existed where the 

 Sierra Nevada is now must have been in existence for very long 

 periods, for each mountain system was reduced by erosion of 

 streams and the weathering agencies to ridges and hills of only 

 moderate height. The time required for the wearing down 

 of these mountains it is estimated must have been between 

 50,000,000 and 100,000,000 years. 



The Story Is Somewhat Complicated 



The geologic history of the Sierra region is somewhat com- 

 plicated, and the story goes far back in geologic time. The 

 record is long. The history and character of two of the ances- 

 tral mountain systems that have come and gone where the great 

 Sierra range is now are quite definitely known. The facts as 

 to the character of these mountains have been determined from 

 study of the rock formations which form what may be called 

 the roots of the ancient mountains, and are now a part of the 

 present range. The approximate time when these earlier 

 mountains came into existence is indicated by fossil remains 

 preserved in the rocks. Each geologic epoch is known by its 

 characteristic life forms. 



Present Range the Latest of a Series 



The first of two ancestral mountain systems that existed 

 before the Sierra range was formed came into being near the 



