28 



GEOLOGIC GUIDEBOOK ALONG HIGHWAY 49 



[Bull. 141 



to cut deeply into a rising surface and to become entrenched even to the 

 rrauite core of the mountain ranjre. Thoujrh born on 'the volcanic cover, 

 the present streams have thus cut much deeper into the bedrock than 

 did the ancient channels. The new streams often cut and robbed fragments 

 of the older Eocene channels and washed their prravels and their <rold into 

 the recent river beds. 



This the forty-niners soon found out and followed the <rold to its 

 source, often by drift miningr under the volcanic cover where it had not 

 yet been removed by erosion. They found that the richest placers were 

 those of white quartz <rravels not intermixed with the softer volcanic ash. 

 They found that the richer ancient channels generally followed the trend 

 of the geologic structure of the bedrock, which once guided their course, 



} 



\ 



. . p<l !>y h\'(lr;ui- 



lickini; ill tlif Omi'Kii mine. I*>cl(i\v the Knivi 1 ! is tin- hcdrock schist mill ;it the contact 



is the concentration of plucer solil. Aliove the snivels lire tiner-^niined deposits of 

 snnd anil Hiiy which have lieen partly washed away. 



while the later streams in the volcanic ash lay athwart the direction of the 

 buried hills and valleys. They found that the rhyolite ash or "pipe-day." 

 frenerally lay directly upon the earliest quartz "ravels and in places these 

 gravels and their <rold had been robbed by intervolcanic water courses 

 which were also buried alou; with the p]ocene {Travels. 



The complexity of the structure of all these inter-related <rravd chan- 

 nels is extreme, and for that reason the distribution of the jrold within 

 them is variable. The whole story is closely interwoven with the earlier 

 history of the bedrock, the position of ^old-bearing veins in the bedrock, 

 and their removal and redeposition by erosion. We are still far from hav- 

 ing solved the complete history of these intricate events which resulted in 

 the unique and interestiii<r features of the Sierran Gold Belt. 



Kid. .'!. Clay pit in the lone fornintioii I Koccnc I south of tin 1 town of 

 lone. Aniiidor Comity. 



