70 



C. K. KEYES INTEEMONT PLAINS OF THE ARID REGION 



its own and that has no genetic relation with any other plain is a deduc- 

 tion that is in strict accord with the known effects of certain plain- 

 forming desert agencies. If we can ascribe to the wind the chief erosive 

 influence or gradation process, there is no baselevel to attain, as in the 

 case of normal erosion by water. At the same time there can be the 



Sierra Ndada 











■ — NJ2000' 





Argus Range , 



^-^9000' 



Panamint Range 



/~\^ 8000' 



Grapevine Ran&e 





Owen 

 \ Valley 

 \ Aooo' y 



\ Panamint 

 \ valley 



\ 1200' 



/ \ Death 



^.,,^6000' 



/ \ Amargosa 

 / \ Valley 





/ \ tsoo' 









\ / 







.SfA.LEVEL.... 







.... _ .\ -500' / 

















Figure 5. — Profile of Death Valley Region, California 



numerous local levelings in a much broken region like the Great basin, or 

 a general leveling of a vast undisturbed area, as in the case of the interior 

 tableland of South Africa. This, however, is a theme for special discus- 

 sion and more extended consideration than can be given it here. 



COURSE OF THE COLORADO RIVER 



After leaving its Grand canyon, the Colorado river still flows nearly to 

 its mouth in a deep valley which has been corraded through a line of 

 mountain-locked basins. This part of the river's course has been fre- 

 quently pointed to as an illustration of a region throughout which great 

 thicknesses of recent sediments have been deposited over the intermont 

 plains.'' 



Deep-well records are given as the chief evidence supporting the opin- 

 ion that the valleys are floored with recent debris to great depths. The 

 uncertainty of these records has been already pointed out. Lee states in 

 j\o uncertain terms that — 



"Over a large part of the Southwest, extending from New Mexico to the 

 Pacific ocean, detrital material fills the low places generally and transfoniis 

 into broad detrital plains districts which might otherwise have very uneven 

 surfaces. In Arizona, where the writer has observed the deposits most widely, 

 the detritus occupies the lowlands to the south and west of the Colorado 

 plateau." 



It may be that the long basin extending southward from the mouth of 

 the Virgin river, and which the author just quoted calls the Detrital- 



" Bulletin of the Geological Society of America, vol. 17, 1906, p. 275. 



