2 



University of California Publications. 



[Geology 



INTRODUCTION. 



This region, which the writer has termed the Upper Region 

 of the Main Walker, is situated between latitudes 39° 10' and 

 38° 58' 48". and longitudes 119 : and 119° 22' W., in the western 

 part of the Great Basin. It is thirty miles due east of Lake 

 Tahoe, and twenty miles southeast in a direct line from the 

 Comstoek Lode of the famous Washoe District. It is seventy 

 miles northwest of the Esmeralda Formation. To reach it one 

 may go by railroad from Eeno, Nevada, to Wabuska, a dinner 

 station on the C. C. railroad, the distance from Reno being 

 seventy-eight miles. 



The earliest notice that this region received was by Fremont 

 while on one of his explorations in search of a route to the 

 Pacific Coast, and in later times it has been sought by the stock- 

 man, ruralist and miner. The river received its name from the 

 great explorer who gave it in honor of Joseph Walker, a noted 

 scout and guide ; and while on the ridge through which the West 

 Walker flows for the purpose of joining its confluent, the East 

 Walker, he ventured an opinion concerning the character of 

 the rocks composing the ridge. 



The region has not, however, received special attention at 

 the hands of any geologist. The mention it has received has been 

 mainly cursory or in a subsidiary connection ; and recently 1 as 

 incidental to a reconnaissance of Nevada and part of California 

 south of the fortieth parallel of latitude. 



The region being somewhat removed from other fields that 

 have been studied, its investigation has been undertaken in the 

 hope of contributing some independent observations to the geo- 

 logical history of the Great Basin, of which it forms a small part. 



The rock series of the Upper Main Walker fall naturally into 

 two major divisions corresponding to the Bedrock Complex and 

 Superjacent Series of the Sierra Nevada. 



The Bedrock Series comprises shales and limestones in a 

 closely folded condition invaded by large intrusive masses of 

 granite and granite porphyry and by dykes of quartz-porphyry 

 and porphyrite. The Superjacent Series, reposing in uncon- 

 1 Spurr, U.S.G.S. Bull. 208. 



