4 



University of California. 



[Vol. a. 



Station were probably largely buried under detrital slopes and 

 the Upper Pliocene sandstones until the opening' of the Quater- 

 nary era. To explain the presence in late Pliocene time of the 

 sea in that basin some mountain has to be eliminated, and the 

 evidence indicates the highest of the region, the Fraser-Pinos 

 Range. Even if we will not agree that the Upper Pliocene 

 sandstone was at one time more extensive and covered the site 

 of Fraser Mountain, a projection of the plane of the base of the 

 sandstone series up the slope of the mountain will convince the 

 student that in late Pliocene time the site of Fraser Mountain 

 was a surface not appreciably elevated above sea-level. There 

 is no faulting of any unusual type of deformation apparent. In 

 Quaternary time Fraser Mountain has been lifted to an altitude 

 exceeding 8,000 feet, and most of this elevation was accom- 

 plished during the disturbance immediately succeeding the 

 Pliocene period. 



The same argument applied to the Upper Pliocene basin 

 in the Santa Clara Valley will lead to the same result. The 

 high mountains almost enclosing the basin owe their present- 

 prominence chiefly to uplift in early Quaternary time. This is 

 especially true of the great mother range of Southern California, 

 the Sierra Madre-San Bernardino Range, which has an average 

 altitude exceeding 6,000 feet and several peaks reaching 10,000 

 and 11,000 feet. 



The only extensive portion of Southern California, so far as 

 seen by the writer, apparently remaining nearly in its late 

 Pliocene condition is the Mohave Desert. Professor N. S. Shaler 

 says* of it: "The most complete effacement of the original 

 valleys appears to have taken place in the region known as the 

 Mohave Desert. Here the detrital slopes have risen to near the 

 tops of the ranges." I entered the region with that idea in 

 mind and came out convinced that it requires a radical modifi- 

 cation. There are, indeed, thick accumulations of detrital 

 material that have been built up close to the foot of such 

 prominent ranges as the Tehaehapi and the Sierra Madre, and 

 may have buried the foot-hills, but iu the central and by far the 

 larger portion of the desert region I do not believe the detrital 



* Broad Valleys of the Cordilleras, Bull. Geol. Soc. Amer., Vol. 12, p. 290. 



