Hershey.] 



Quaternary of Southern California. 



23 



extended from wall to wall. From the rate at which it was 

 hurrying the coarse granite sand along its bed, I gained the idea 

 that it has considerable eroding power. It seems rational to 

 compare this gorge with certain rock gorges in the drift area of 

 the Eastern States. Considering the hard rock and the nature 

 of the stream, the absence of falls or rapids indicates that the 

 gorge-cutting was begun at a date earlier than the Iowan 

 epoch, and probably as far back nearly as the Illinoian. This 

 corroborates an estimate which I derived from the broad valley 

 that the uplift and consequent dissection of the Quaternary 

 detrital and alluvial gravels which bound Mohave River Valley 

 in bluffs two hundred feet high for many miles, began at the 

 close of the Red Bluff epoch. 



I also gained the idea in the Mohave Desert country that the 

 great detrital slopes were virtually completed by the close of 

 the Red Bluff epoch. They do not seem to be appreciably 

 increasing to-day. If they were growing as vigorously now as 

 they once were, here and there they should be found creeping 

 into the canons which have been in process of erosion since the 

 Red Bluff epoch. In places these canons cut off the outer 

 portion of a detrital fan, stopping its growth at the end of the 

 Red Bluff epoch, yet it continues to correspond to the slope 

 above. A later series has formed in the larger canons, but its 

 members are insignificant in comparison with those which form 

 the floors of the broad basins. I believe that the greater part 

 of the detrital and old alluvial material of the Mohave Desert 

 region (Antelope Valley excepted) belongs to the Red Bluff 

 formation. The general depression of the Red Bluff epoch 

 brought about some climatic conditions which especially favored 

 the formation of detrital slopes, and the subsequent uplift 

 terminated those favorable conditions. 



Just south of Victorville the Mohave River traverses another 

 granite spur in a short gorge no wider than the stream at low 

 water and having very steep walls. Above it the river 

 crosses a broad basin occupied by the Quaternary deposits and 

 has excavated its usual broad, shallow valley. 



The floor of Antelope Valley rises steadily from Victorville 

 to Summit Station (altitude about 4,000 feet). The railway 



