BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 15, PP. 289-346, PLS. 14~21 JULY 15, 1904 



BASIN RANGE STRUCTURE OF THE HUMBOLDT REGION* 



BY GEORGE DAVIS LOUDERBACK 



{Presented before the Society January i, 1901f) 

 CONTENTS 



Page 



Introduction , 291 



The Humboldt Lake mountains 294 



Location and extent 294 



The bedrock complex 295 



General composition and character 295 



Lithological character 295 



Folding 296 



Faulting 297 



Thrusting 297 



Alteration : 298 



Geomorphic relationships .. 298 



Eelation to range outline .... 299 



Igneous rocks 300 



Summary. . , 300 



The superjacent series 301 



General composition and character 301 



Sedimentary rocks 301 



Truckee beds 301 



Lahontan beds 301 



Alluvial and % recent deposits • 302 



The volcanic rocks 302 



General character and relations 302 



Rhyolite tuffs 303 



Rhyolite lava 304 



Basalt 304 



Structure and distribution of the volcanics 305 



Mountain movements indicated by the volcanics 306 



Petrographical descriptions and comparisons of Summit and West Base 



basalts 309 



> 



* Published by permission of the Carnegie Institution of Washington. The main points of the 

 paper, as far as the Humboldt Lake range is concerned, were presented before the Cordilleran 

 section of the Society December, 1902. Another field trip was made in June, 1903, for the purpose 

 of getting a more accurate topographic section and of extending the work to Table mountain. 

 The latter trip and preparation of results was made by the writer as research assistant of the Car- 

 negie Institution. The writer is indebted to Professor G. J. Young for surveying, by transit and 

 stadia method, the profile for the detailed section. 



XXXVIII— Bull. Geol. Soc. Am., Vol. 15, 1903 (289) 



