204 



GUIDEBOOK OP THE WESTERN tTNITED STATES. 



low relief. By the elevation and westward tilting of this surface the 

 Sierra Nevada was formed. 



The rocks near the summit are principally granite (or gi^anodiorite)/ 

 lavas (andesite, rh^^olite, and basalt) , tuffs, and breccias. The vol- 

 canic rocks generally cap the ridges, the canyons being cut through 

 them into granite or into sedimentary rocks which have been invaded 

 by the granite. In general, throughout the western slope of the Sierra 

 Nevada, the lavas, the associated gold-bearing gravels, and the other 

 Tertiary rocks he nearly horizontal on the worn surface or eroded 

 edges of a much older tilted set of rocks. These older rocks comprise 

 altered sediments, such as slates and schists, altered lavas and tuffs, 

 in part rendered slaty or schistose by pressure, and intruded igneous 



masses 



formations 



most 



tinguishable from one another from the train. The 



and characteristic are the Calaveras formation, of Carboniferous age. 



Mariposa slate, of Juras 



Both consist chiefly of slaty 



lins some limesto 

 intrusive masses 



o 



' rocks vai 

 to 70° E. 



Marip 



formations 



take the place of the granite and volcanic rocks 



Cisco- 

 Elevation 5,940 feet. 

 Omaha 1,602 miles. 



one point. 



North of the 

 railroad, on the summit of a high ridge Ivuo^vn as S 

 nal Peak, the railroad company maintains a lookout 

 station, from which a watch is kept for fii'es in the 

 snowsheds, many miles of wliich are in view from this 

 e ridge on which the signal station is situated is com- 



posed of metamorphosed slates (Sailor Canyon formation 

 age, hke those that occur at Cisco. The brown talus from 



is in decided contrast with 

 passed. 



granite 



•s 



previously 



constr 



for the railroad employees. Here also is a summer hotel and camp. 

 In the valley of the South Fork of the Yuba below the railroad, on the 



summer 



and forms a section of the recently named Lincoln Hi 



openings 



at places where one part of the shed 



6 



IS ma 



to telescope into 



another, being mounted on wheels for that purpose. These 



mass 



^ The granodiorite of the Sierra N' 

 is an enormous mass of intrusive rod 

 partly bared by erosion. Such a 

 that extends to unknown depth is called 

 by geologists a batholith. The bathoKth 

 of the Sierra Nevada is merely one mem- 



ber of a chain that comprises many such 



masses 



coast o 



3f North America. These immenFe 

 bodies of igneous rock were intruded in 

 late Jurassic or Cretaceous time and may 

 all be connected at gi-eat depth. 



