342 University of California Publications in Geology [Vol. 13 



mouth of Blaisdell Canon and Snow Creek are as high as 6°. They 

 approach the ideal more closely than do those of the north in that the 

 material of which they are composed is more angular. It has not been 

 subjected very much to the action of running water, but has simply 

 been carried out on the fans and deposited. No streams flow down 

 over them except after the rains. On the other hand, the slope of the 

 Whitewater fan is very gentle and much of the material is so rounded 

 that it might well be called stream conglomerate. A considerable 

 stream flows down throughout the year and as late as July it amounts 

 to more than 2000 miner's inches. Comparison of other opposing 

 streams reveals the same relationship though not with such a marked 

 contrast. 



To sum up the situation it seems that the fans from the north are 

 the more extensive because of the greater amount of water contributing 

 its load to them. 



Summary 



The four cycles of erosion in the San Bernardino Mountains show 

 that the mountain mass has reached its present position of elevation 

 by stages. To be sure, changes in aridity have had some influence in 

 sculpturing the horsts, but in the main the record is of uplift. 



Previous to the first movement and during the first cycle the region 

 was reduced to a peneplain, and following it the broad graded valleys 

 of the second cycle were cut below this erosion surface. Therefore the 

 difference in elevation between the remnants of the surface of the first 

 cycle and the broad valley floors of the second indicates the amount 

 of the uplift. The summit ridge between San Bernardino and San 

 Gorgonio mountains rises 4000 to 4800 feet above Big Meadows and 

 the floor of Bear Valley. These figures approximate the maximum 

 movement between the development of the first and second cycles of 

 erosion. 



The amount of the second uplift is not so clearly recorded as that 

 of the first. After it was accomplished Santa Ana Canon was cut 

 below the floor of Bear Valley about 1000 feet, but this figure tells 

 little since the stream had not reached base level before a change in 

 humidity arrested its cutting action and caused the V-shaped canon 

 to be filled with debris. Along the south front of the range, however, 

 it appeal's that there has been no important vertical movement on 

 either the San Andreas fault or Mission Creek fault since the develop- 

 ment of the third cycle. It would seem, therefore, that elevation of 



