Si University of California Publications in Geology [Vol. 9 



it is evolved, or the conception of it as a quasi limiting stage of the 

 degradation cycle of the desert. Appreciation of the process enables 

 us to understand certain features of the desert relief which are other- 

 wise unintelligible ; and without the concept of the desert cycle, as 

 here defined, it is impossible to read the geomorphic history of such 

 regions. 



From the foregoing discussion it is apparent that bold relief in 

 the desert is subdued partly by degradation and partly by aggradation 

 in reciprocal relation, and that the degradational process produces two 

 rock surfaces, one of which vanishes at the close of the cycle while the 

 other then attains its maximum extent. The former may be referred 

 to as the subaerial front and the latter as the suballuvial bench. 

 Neither of these rock surfaces is in evidence at the panfan stage of 

 the cycle. The subaerial front has been reduced to nothing and the 

 suballuvial bench is, as at all stages, buried. If, however, there be 

 introduced at some part-way stage a diastrophic movement which not 

 only interrupts the normal course of the cycle, but also promotes the 

 destruction of the alluvial embankment, then we may by resurrection 

 have the suballuvial bench revealed as an element in the visible 

 profile. Such stripping of the fans might be effected by faulting or 

 doming which would increase the angle of the surface slope. A 

 general elevation of the region without local faulting or doming might 

 produce the same result, if precipitation upon the summit region were 

 thereby increased to the extent of supplying streams competent to 

 dissect the fans. 



Such diastrophic or climatic interruption of the normal course of 

 the desert cycle, resulting in the stripping of the upper parts of the 

 embankments, affords the probable explanation of certain broad rock 

 terraces which are found on the flanks of some of the desert mountains 

 of California, Nevada, Arizona, New Mexico and Mexico. 



Such rock terraces have been described by McGee, 6 who ascribed 

 their origin to sheet flood erosion, and by Paige, 7 who dissents from 

 McGee 's hypothesis of sheet flood erosion and correctly interprets 

 them as resurrected surfaces due to the stripping ot the alluvium 

 which once rested upon them. 



The Suballuvial Bench. — The general genetic relations of the sub- 

 alluvial bench having been stated, some details of its configuration and 

 of the law governing its development may briefly be discussed. Neither 



e Bull. Geol. Soe. Am., vol. 8, pp. 87-112, 1897. 

 i Loc. ext. 



