330 University of California Publications in Geology [Vol. 13 



Bear Valley was developed near base level and uplifted by movement 

 on these faults. It is therefore evident that this mature surface along 

 the south front of the range must represent a far younger surface than 

 that of the Bear Valley region and is probably correlative with the 

 Santa Ana or third cycle. 



Around the headwaters of Whitewater River are extensive flats 

 which once formed the floors of mature valleys, but are now deeply 

 dissected. Ray wood Flat (pi. 21 A) is a remnant of one of these old 

 floors, but others are numerous and, as seen from one of the hills, they 

 all seem to form a continuous surface. As is the case in Santa Ana 

 Canon, they consist of fanglomerate and therefore represent extensive 

 filling after the earlier excavation of the canons. In discussing the 

 structure it will be seen that the Mission Creek fault probably crosses 

 this area. But there is no offset. This is, of course, in keeping with 

 the statement that the surface belongs to the third cycle. 



The topography of the Bear Valley area is more complex even 

 than as described in preceding pages, for in many places there may 

 be found evidence of subcycles; but the relationships between them 

 in different areas are hard to determine. The ridge on the south side 

 of Bear Valley broadens out toward the west and in the vicinity of 

 Bluff Lake there is a considerable area of flat country which lies 700 

 feet above Bear Lake. This locality is a region of broad meadows 

 separated by low but extremely rugged ridges (pi. 20B) . The rounded 

 forms taken by the granite are not due to exfoliation, but to a sort of 

 crumbling of the disintegrating granite. This surface lies at about 

 the same elevation as the bench between Rathbone Creek and Erwin 

 Lake and the tops of the ridges farther east. Broom Flat and Cienaga 

 Seca may also belong to this subcycle, although they lie at different 

 elevations. 



The streams down from the ridge west of Sugarloaf have very low 

 gradients in their upper courses, i.e., near the crest of the ridge, while 

 farther down they drop off precipitously. This condition is most pro- 

 nounced near Sugarloaf itself. Northeast of the long ridge a mile 

 east of Sugarloaf there is a small but well defined valley having a 

 southwest course. Other valleys are found near by at about the same 

 elevation. A similar topography is seen just below the crest of the 

 ridge between San Bernardino and San Gorgonio peaks. 



In lower Mill Creek Canon and at the mouth of Potato Canon the 

 conditions were similar to those in Santa Ana Canon, but only small 

 remnants of fanglomerate remain. In Mill Creek Canon these grade 



