TOPOGRAPHY 187 



trail, Sturtevants Camp trail, Mount Wilson- West Fork-Pine Flats trail, 

 Chillao canyon, mount Waterman, Alder creek, upper Tujunga canyon, 

 and, in the region west of Pasadena, Devils gate and the southern por- 

 tion of the San Rafael hills. 



As no topographic maps of the region were available at the time of 

 the inauguration of the work, no effort was made to map the different 

 rock areas, and as a consequence not as much information concerning 

 the relations existing between the different types was obtained as would 

 have been the case had the work included detailed field differentiation 

 and areal mapping. 



Previous Literature 



For an interesting mountainous region of over 1,200 square miles in 

 extent, located in as important a section of country as that in the vicinity 

 of Los Angeles, the San Gabriel chain has certainly received very little 

 notice from geologists. 



Doctor Trask, first state geologist of California, in 1855, referring to 

 the geology of the San Bernardino mountains (in which he includes the 

 San Gabriel and all other ranges from the San Jacinto to the Santa 

 Inez), says : * 



"These mountains are made up for the most part of the primitive rocks, and 

 consist chiefly of the granitic series. They form by far the most of all the higher 

 ridges and more elevated peaks belonging to the chain." 



In 1857 Blake f in his Pacific Railroad Survey report mentions com- 

 pact and gneissose granite, talcose slates traversed by quartz veins, and 

 trappean rock as occurring in the Cajon pass. 



Slate, hornblende rock, and gneiss were found by Whitney, X state 

 geologist from 1860 to 1874, as float in the mouth of the San Gabriel 

 canyon. 



In 1900 Claypole § presented a paper on the " Sierra Madre near 

 Pasadena " before the Cordilleran Section of the Geological Society of 

 America, in which he described that range in a very general way, dwell- 

 ing mostly on its relation to the region south of it. 



Hershey || in 1902 mapped the western end of the San Gabriel moun- 

 tains as'"plutonic" and the eastern end as " granite." He also men- 



* J. B. Trask : Report on the geology of the Coast ranges. Cal. Sen. Doc., no. 14, 1855, p. 20. 

 t Wm. P. Blake : Pac. R. R. Report, vol. v, 1857, p. 88. 

 X J. D. Whitney : Geol. Survey of California. Geol., vol. i, 1865, p. 172. 

 I E. W. Claypole : Bull. Geol. Soc. Am., vol. 12, 1901, p. 494. 



(I O. H. Hershey : The Quaternary of southern California. Bull. Dept. Geol. Univ. of California, 

 vol. iii, 1902, no. 1. 



