184 ARNOLD AND STRONG — CRYSTALLINE ROCKS OF SAN GABRIEL 



at Leland Stanford Junior University, and which have been continued 

 intermittently ever since. The analyses were made by the junior author 

 in the laboratories of the university. The writers are indebted to Dr 

 James Perrin Smith, of Stanford University, and to Dr Waldemar Lind- 

 gren, of the United States Geological Survey, for helpful suggestions 

 relating to the preparation of the paper. 



Location of the San Gabriel Mountains 



The San Gabriel mountains are a group of more or less intimately 

 associated ridges and peaks occupying the territory between Cajon pass, 



j&rrre 



Figure 1.— Sketch Map of Southern California. 

 Showing relation of the San Gabriel to the other mountain chains. 



in San Bernardino county, and the Santa Clara river, in Los Angeles 

 county, their greater portion lying in the latter. They comprise an area 

 of about 50 by 25 miles, nearly all of which lies within the confines of 

 the San Gabriel timber reserve. The chain is exceptional in that its 

 axis lies oblique to (and in some instances nearly perpendicular to) those 

 of most of the other prominent ranges of California. What genetic rela- 

 tion exists between this group and the Sierra Nevada, Mount Diablo, and 

 other ranges north of it is yet to be determined, but much light will 



