The Geological Story Briefly Told 73 



erous (Palaeozoic) age occur, bent, folded, and wrinkled by 

 mountain upheaval, and farther west on the lower slope are 

 rocks of Jurassic (Mesozoic) age, also contorted by mountain 

 upheaval and compression of the rock strata. Both these groups 

 of sedimentary rocks have been metamorphosed by the great 

 heat and pressure of mountain building from the original muds, 

 sand and lime into slate, quartzite, and marble. Extending 

 through the belt of metamorphic rocks is a group of gold- 

 bearing quartz veins, the Mother Lode, made famous in the days 

 of '49. These upturned beds are the remnants of the worn and 

 eroded folds and wrinkles of sedimentary formations that were 

 upheaved and metamorphosed in the upheavals of mountain 

 building that preceded the great final upthrust of the Sierra 

 Range. 



Earliest Upheaval of Sierra Nevada 

 Near Close of Palaeozoic Era 



The earliest mountain upheaval of which we have definite 

 knowledge in the region of the present Sierra Nevada Range 

 occurred near the close of the Palaeozoic era, in the Permian 

 period. This is estimated to have been more than 200 million 

 years ago. This ancient mountain system was formed by the 

 uplifting and folding of a great series of layers of slate, shale, 

 and sandstone, rocks that were originally mud, silt, and sand 

 derived from a land mass lying mostly to the west of the present 

 border of the continent and laid down in an arm of the ocean. 

 After the uplifting of this ancestral mountain system there 

 ensued a long period of erosion. The mountains were gradually 

 worn down. During millions of years the persistent weathering 

 of the rocks and the erosion of streams reduced the mountains 

 to ridges and hills. What had been a great mountain system 

 became reduced to a rolling plain with moderate hills. Then 

 after the lapse of perhaps 40 to 50 million years the land again 

 sank and was covered again by the sea and became a place of 

 deposition. For millions of years new layers of mud, silt, and 



