402 University of California Publications in Geology [Vol. 13 



On the east side of a small ridge three miles west of Mission Creek 

 fanglomerate dips sharply down against a vertical contact with the 

 schists which have been raised on the north. 



Farther west this fault is in alignment with a branch of White- 

 water River and then with Mill Creek, which is remarkably straight 

 despite the heterogeneous character of the rocks on either side. The 

 ridge on the north has a long even crest regarded as a remnant of an 

 old surface. That on the south side is also rather even, but is 2000 

 feet lower. The crest lias gently rolling hills and inclosed basins 

 which are certainly abnormal in their present position. Headward 

 erosion could hardly reduce a ridge to such an extent still maintaining 

 an even crest. Of course there is the possibility that at an earlier 



Fig. 11. The Mission Creek fault northeast of Hog Ranch showing schist 

 overthrust on fanglomerate. 



date in the history of the topography of the mass this outer edge of 

 the block was reduced nearly to base level before the northern ridge 

 was attacked. Bearing in mind the other evidence of faulting, how- 

 ever, it seems probable that it was never raised to the same height as 

 the north side. If, then, the present relationship is due to faulting, 

 differences in elevation on the map show that the ridge between Potato 

 Canon and Mill Creek has been raised 3000 feet, and the ridge north 

 of Mill Creek 5000 feet above the floor of the San Bernardino Valley, 

 which lies to the west just off the map. This valley floor is not a 

 portion of the surface which was once continuous with the crests of 

 the ridges, but consists of sediments from the surrounding mountains. 

 The old surface itself is probably buried beneath them. It is there- 

 fore evident that the elevations of the ridges above the present valley 

 floor do not represent the total uplifts of the blocks nor can these be 

 exactly determined. 



The divide between Mill Creek and Whitewater was examined 

 for evidence of displacement of rocks by faulting, but as the whole 

 country rock is schist these observations were not entirely satisfactory. 

 Comparing the rocks on either side of Mill Creek at this point, it is 



