328 University of California Publications in Geology [ VoL - 13 



edges of this area to show that the formation of the bench and sur- 

 rounding hills is the work of an earlier cycle. Between Wallace Creek 

 and Cherry Canon and extending up Hog Canon and Little San Gor- 

 gonio are flat areas which are at the same general elevation as Ban- 

 ning Heights and belong to the same old surface. Similar benches are 

 seen on the east side of San Gorgonio River. 



At the head of Hathaway Canon and extending over to Potrero 

 Canon there is an open valley with a smooth granite floor. It could 

 not have been developed in its present position by normal erosion, for 

 that would have left a high ridge between the two canons. The sim- 

 plest explanation is that it must be part of an old surface faulted down 

 and thus protected. (See structure.) Just when this surface was 

 developed is a question. It may be part of the second cycle or even 

 of the first. 



On both sides of Millard Canon the contrast between the upper 

 and lower slopes of the foothills is remarkable. On the flanks of these 

 hills the slopes are steep and free from soil ; the small gullies are V- 

 shaped and have high gradients. In the upper portions the slopes 

 are well rounded and the soil is thick and supports a dense growth of 

 brush. These facts indicate a mature topography before the cycle was 

 interrupted. A horizontal stratum of gravel resting on schist near 

 the top of the hill on the east side of Millard Canon at its mouth serves 

 to make the distinction between the old cycle and the present clearer. 



Farther east the old surface is even more prominent. It includes 

 the upper portions of the ridges between Millard and Cottonwood 

 canons since on these there are so many flat areas at an elevation of 

 about 3500 feet that there appears to be a plain at that level above 

 which rise low rolling hills. Some parts of this area are worthy of 

 special mention. At the upper end of Deep Canon on the west side 

 there is a long bench just below the crest of the ridge. Over the ridge 

 to the north is a small depression which, until recently, was undrained, 

 but it is now reached by a small side-canon from Millard Canon. West 

 of the first branch of Stubby Canon there is a similar basin which still 

 has no outlet. Such basins may be developed almost anywhere along 

 a fault and are, indeed, important rift features ; but here they form a 

 part of an old surface which, it has already been suggested, was de- 

 veloped during arid conditions. They are often found in the desert 

 and may be structural or formed by deflation. Certainly they must 

 be considered as indicative of aridity, for in a humid climate they 

 would soon be filled with sediments brought in by streams. 



