86 



GEOLOGIC GUIDEBOOK ALONG HIGHWAY 49 



[Bull. 141 



and resorts. Sardine Lake must be reached by foot from Sardine Creek 

 public camp. 



From the vicinity of Bassett to the summit of the pass, the basement 

 rocks are weathered granodiorites of the main pluton or batholith which 

 forms the core of the Sierras. Spheroidal decay boulders can be seen 

 weathering out of the main granitic mass in' many places. Preservation 

 of more or less unaltered spheroids in an almost completely weathered 

 matrix is typical of granitic masses in a great many other places as well 

 as the Sierras, and is a phenomenon which has never been adequately 

 explained. Local differences in grain size and mineral composition some- 

 times account for it. In other instances the effect has no apparent local 

 control. 



The summit of Yuba Pass, at an elevation of 6701 feet, lies in a broad, 

 upland valley which is slowly being dissected at either end by streams 

 of opposing watersheds. The winding grade from Yuba Pass to Sattley 

 affords fine views of Sierra Valley which opens out to the northeast from 

 the vicinity of Sierraville. Sierra Valley is a graben or depressed fault 

 block part of which has been masked by volcanic mountains extruded 

 since the depression of the block. Subsequent erosion and glaciation has 

 greatly dissected the disrupting lava. William Morris Davis believed 

 Sierra Valley to be a continuation of the graben which is partly occupied 

 by Lake Tahoe. The fault which roughly corresponds with the western 

 edge of the valley crosses Highway 49 immediately west of Sattley. 

 Andesitic gravels can be seen faulted against the granodiorite in places 

 where the contact is not masked by alluvium. 



Highway 49 joins Highway 89 at Sattley, Sierra County, thus termi- 

 nating 277 miles of mountain road which began at the Highway 49- 

 Highway 120 road junction at Mariposa in Mariposa County. Virtually 

 the entire streach lies in gold mining country within the Sierra Nevada. 

 Few routes through California are as replete with historical color as this 

 Golden Highway. 



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