1922] 



Vaughan : 



Geology of San Bernardino Mountains 



329 



This old surface may be traced over the upper parts of the hills 

 between Cottonwood and Whitewater canons. It continues up the 

 latter on both sides for several miles and is particularly prominent 

 near Red Dome, where it takes the form of a bench on the west side of 

 the canon and a flat-topped ridge on the east. From this point it con- 

 tinues northward to Mission Creek. A line along the face of the hills 

 east of Mission Creek continued westward is the locus of a series of 

 longitudinal gulches. It seems that here there was once a valley with 

 gently sloping sides and floored with a considerable depth of fan- 

 glomerate. The present streams are influenced by this old valley ; 

 they tend to follow it and are removing the old floor. 



Near the head of Mission Creek and in the upper courses of Big 

 and Little Morongo creeks extensive benches merge into the sides of 

 the canons. They are very similar to Raywood Flat, and, like it, are 

 composed of fanglomerate and have been cut by recent erosion. 



Morongo Valley consists of two parts, Upper Morongo, which is 

 included in the San Gorgonio Quadrangle, and Lower Morongo, which 

 lies to the east. They are separated by a divide shown on the edge of 

 the map. Along the southeast side of Upper Morongo there is a strip 

 of fanglomerate and on it there are remnants of a topography of low 

 relief. North of the divide this surface may be seen developed on the 

 granite. 



There are some interesting points to be considered in connection 

 with the topography along the south slope of the range. In a later 

 section it will be shown that a fault traverses Potato Canon to Pine 

 Bench, thence to the mouth of Stubby Canon, and thence nearly 

 straight east beyond Whitewater River. While there are frequent 

 depressions marking the position of this fault, there is no actual off- 

 setting of the topography, although the fault crosses several flat places 

 in the old surface that would surely record such a movement. On 

 the west side of Whitewater River fanglomerate on the south side is 

 faulted down against the schist on the north ; but the flat surface 

 passes over the contact with no sign of a break. The fault crosses the 

 flat remnant of the old surface on the west side of Deep Canon, but 

 again there is no offset. So it is quite clear that the old surface is 

 later than the most recent vertical movement on the fault at this 

 locality. One mile and a half northwest of Hog Ranch another rem- 

 nant is found on a ridge parallel to the Mission Creek fault ; but at 

 the southeastern end of this area it is hook-shaped and crosses the fault. 

 Here again the flat surface must be later than the faulting. Now 



