TOPOGEAPHIC FEATURES OF THE DESEET BASINS; 55 



tion. Valleys dammed by alluvium, local depressions dried below 

 their outlets, ponds like those of the Great Plains and coulees, as well 

 developed as those of Washmgton, all abound. Many of these inclosed 

 areas are of considerable salinity, but all are recent and most are tiny, 

 and it does not seem necessary to discuss them in detail. In area 

 they vary from ponds or playas that drain a few acres to the large but 

 shallow basin of the plains of San Augustine m western New Mexico, 

 compassing perhaps 1,500 square miles. This latter basin and the 

 smaller ones in its vicinity probably once drained into the Rio Grande 

 instead of the Colorado, but otherwise they do not differ from their 

 western analogues. In the absence of fuU and detailed knowledge of 

 the entire plateau region it is impossible to deny categorically the 

 existence of basins, the size or antiquity of which would give them 

 present interest. However, it seems very probable that, with one 

 exception, no such exist. This exception will now be described. 



THE HUALPAI BASIN. 



In its southwestem portion the Colorado plateau has been more modified than else- 

 where, both by movement and erosion, and here lies the Hualpai or Red Lake Valley, 

 occupying a depression in the making of which both movement and erosion have had 

 a hand . There is little doubt that this valley once drained northward to the Colorado, 

 but this drainage may have been a long time ago. The present divide, though allu- 

 vial, is high and may be pre-Lahontan. The writer, while inclining to the opinion 

 that it is, does not care to advance any conclusion. The area of the basin is 

 approximately 1,450 square miles and its deepest depression contains a playa which 

 is not known to be especially saline. 



THE PONDS AND COULEES i OF EASTERN WASHINGTON. 



The central and eastern part of Washington is largely a great lava 

 plateau, somewhat warped and cracked by the movement which was 

 more pronounced farther south and west, but preserving much of its 

 original character. Being of little relief and in general of poorly devel- 

 oped drainage, this plateau has suffered severely by desiccation and is 

 now dotted with literally hundreds of small inclosed basins, due prima- 

 rily to inequalities in the lava surface and resembling in every way the 

 small pans of the Christmas Lake, Abert and Alkali Valleys, as dis- 

 cussed on pages 22 to 26. Some of these depressions now carry per- 

 manent or intermittent lakes, most are slightly or moderately saline, 

 but all are recent and owe their inclosed condition to the decay of the 

 drainage system to which they once belonged. So far as known none 

 drain an area of over a few square miles and none. are important. 



Another and less usual type of inclosed basin is represented by the 

 ''coulees," or long, narrow valleys with steep walls and flat floors, the 

 floors being dotted with lakes. Essentially these are old stream chan- 

 nels, the history of which, stripped of all details, is as follows. When 

 the lava plain was uplifted and warped, numerous cracks formed 



I The word "coulee" is here used as locally understood. 



