1922] Vaughan: Geology of San Bernardino Mountains 321 



TOPOGRAPHY 



General Statement 



Near the eastern margin of the San Gorgonio Quadrangle there is 

 a break in the San Bernardino Range, the most noteworthy features 

 of which are Morongo Valley and a valley in the region east and north 

 of The Pipes. To the east the mountains are much lower than to the 

 west, where they rise gradually to their maximum height at San Gor- 

 gonio Mountain. About eight miles north of this is another important 

 summit, Sugarloaf Mountain. From these two peaks the range is 

 unbroken westward to Cajon Pass. 



San Gorgonio Mountain is near the eastern end of a high ridge 

 between two of the largest streams in the area, Santa Ana River on 

 the north and Mill Creek on the south, both of which flow westward 

 in deep canons. South of Mill Creek there is another ridge parallel 

 to that on the north. 



The country north and northwest of Sugarloaf presents an old 

 geomorphie surface. Here are found broad valleys with meadows at 

 a general elevation of 7000 feet above sea level ; and the hills have 

 rounded profiles. The most important valley is Bear Valley, the east- 

 ern extremity of which is four miles northeast of Sugarloaf. It ex- 

 tends westward for twelve miles and is drained to the west by Bear 

 Creek through a precipitous gorge. A dam has been constructed at 

 the lower end of the valley, which retains a lake six miles in length 

 and a mile wide. At the eastern end, separated by a low ridge, are 

 two lakes, Baldwin Lake to the north and Erwin Lake to the south. 



North of Bear Valley, parallel to it and separated from it by a 

 low ridge, is Holcomb Valley, which is of the same general character. 

 There are no lakes here, but at the lower or western end there is a 

 large meadow. On the north side of this valley there is a low ridge 

 and beyond this a precipitous declivity to the desert in evident geo- 

 morphie discordance with the broad valleys and smooth ridges of the 

 uplands to the south. 



East and southeast of the Bear Valley region the mountains are 

 rugged, being traversed by many steep, crooked canons. However, the 

 tops of some of the ridges are smooth, and these are of great signifi- 

 cance geomorphically, for they serve as links between old surfaces to 

 the east and west. 



