hershey.i Quaternary of Southern California . 



1!) 



would cause a certain amount of dissection. However, in the 

 particular area investigated there is evidence aside from the 

 dissection of alluvial plains and detrital slopes that an uplift did 

 occur at the time the dissection began and I feel that we are 

 warranted in considering the relation between them to have been 

 that of cause and effect. The undoubted uplift of the marine 

 Pleistocene is positive proof of an orogenie disturbance of no 

 mean magnitude. Far inland, as at Cajon Pass, (as will be dis- 

 cussed later) , there was orogenie deformation in addition to 

 simple uplift. In several places the dissection of the detrital 

 slopes is clearly due to such deformation and neighboring slopes 

 which were not tilted are not dissected. I suppose that there 

 has been throughout the Quaternary era more or less of variation 

 in the rainfall of Southern California, but such slight evidence 

 as I have been able to gather rather negatives the hypothesis 

 that the time of inception of dissection of the detrital slopes cor- 

 responds to a marked increase in the rainfall. 



Above Acton, Soledad Canon is broad and is flooded by a 

 gravelly plain of waterworn and water-deposited material. It 

 is bounded by terraces from fifteen to seventy-five feet high. 

 These terraces are of horizontally stratified material as exposed 

 in the railway cuts but they rise at a considerable angle to the 

 bases of the surrounding mountains. They represent the detrital 

 slopes of a late Quaternary period. Some disturbance, probably 

 an uplift, caused them to be trenched by the main Soledad 

 Canon and by small tributary canons so that they remain some- 

 what as mesa-like patches. Considering the dry climate, the 

 erosion accomplished places them in the Red Bluff epoch. 



These detrital slopes extend to the summit which the railroad 

 crosses in a rather deep transverse valley (Soledad Pass) suggest- 

 ing that it was once the course of a river draining Antelope 

 Valley; but the material exposed on the floor of this valley, 

 while it is largely waterworn and somewhat stratified, is local in 

 origin, varying as greatly as the composition of the neighboring 

 mountain slopes. These are mostly of a light colored granite 

 until lava is approached just east of Vincent Station, when the 

 valley floor is occupied by a dark red deposit mostly of lava 

 debris, but disposed precisely as is the light colored granite 



