SUBDIVISIONS OF THE AMERICAN ARID REGION 545 



the Colorado plateau does the Great Basin, properly so called, extend. 

 West and south of the high plateau is a centrally depressed plain studded 

 thickly with typical desert ranges. It may be termed the Californian 

 Gulf basin, and may be regarded as reaching down into the sea in the 

 Gulf of California. East and south of the Colorado Plateau province is 

 the northern extension of the Mexican tableland. 



The proper discussion of Basin-range structures requires that the feat- 

 ures of the four subregions should be considered separately. Each pre- 

 sents phases of the different structures so very distinctive that it effect- 

 ually prevents advantageous generalizing for the entire desert country, 



Explanations of the Origin of the Great Basin Eanges 



The several views regarding the origin of the Basin ranges may be, 

 according to the central feature emphasized, tabulated as follows : 



1. Folding: 



.Simple and direct King, 1870. 



2. Faulting: 



Simple and direct Gilbert, 1874. 



Powell, 1876. 

 Simple, previous folding King, 1878. 



Russell, 1884. 



Diller, 1886, 



Le Conte, 1889. 



Simple, previous folding and planing off Button, 1880. 



Com pound, and direct Lauterback. 1904. 



3. Erosion: 



Corrasive, folded and faulted ridges, complex Spurr, 1901. 



Corrasive, faulted blocks Davis, 1903. 



Deflative, flexed, faulted, and planed region, differen- 

 tially eroded by wind action mainly Keyes, 1908. 



In general the diversity of opinion here shown is, as a matter of fact, 

 more apparent than real. The conclusions reached by different writers 

 are, in the main, true for the localities in which the particular investiga- 

 tions were first carried on; they are not necessarily antagonistic to one 

 another, but mutually supplementary. Any seeming shortcomings ap- 

 pear to be due rather to generalization too broad than to incomplete 

 observation. King's first opinion admits of no other interpretation in 

 northern Nevada, nor does it preclude later-date faulting, as suggested 

 by Gilbert. The latter's grand conception seems plain in the Grand 

 Canyon district, where displacement has been manifestly so vast and so 



