TOPOGRAPHIC FEATURES OP THE DESERT BASINS. 39 



main uplift^ that of the San Bernardino Mountains, but the trend is 

 here northwest and southeast, instead of north and south. 



These trends of the basin boundary are paralleled by the troughs 

 within it. In the northern part of this division are four great troughs 

 running very nearly north and south and hence parallel to the Sierra. 

 In the southern portion are two similar troughs, but running north- 

 west and southeast in parallelism to the crest of the San Bernardinos. 

 Between the two sets of troughs is a considerable area of more com-^ 

 plex structure and less pronounced relief. Of the northern troughs 

 the westernmost, under the crest of the Sierra, contains the Owens 

 Valley, with the Mono and Searles Basins to the north and south, re- 

 spectively. The next trough to the east is the Panamint Valley, with 

 what are essentially its northern extensions in the Saline, Eureka, and 

 Deep Springs Valleys. The third trough is that of Death VaUey, and 

 the fourth and last is that of the Amargosa VaUey, with the Pahrump 

 and Ivanpah Valleys cut off from its southern end. The interme- 

 diate zone of less concentrated uplift is mainly drained by the Mojave 

 Kiver, though the Kane, Wihard, Granite Mountain, and Owl Basins 

 lie within it and seem to have been permanently undrained. The two 

 southern troughs parallel to the San Bernardinos belong partly by the 

 Mojave drainage and partly to the former drainage of the Colorado 

 River, being cut by alluvial divides in the same manner as the trough 

 vaUeys of Nevada south and east of the Lahontan Basin. 



THE MONO BASIN. 



The Mono Basin is here classed as belonging to the westernmost or Owens Valley 

 trough of this division, but its structural affiliations are quite as close with the basins 

 of the Nevada transition zone and the classification adopted is entirely arbitrary. It 

 occupies a structural depression of considerable depth, contains the saline Mono Lake, 

 and has always been without outlet. The Quaternary history of the basin has been 

 studied by Russell,^ to whose report the reader is referred for details. One part of 

 the structural basin, the Aurora Basin, is now cut off from the valley of Mono Lake 

 by a divide nearly 300 feet high, but this divide was below the waters of the greater 

 lake which occupied the valley during the Lahontan period, and the independent 

 history of the Aurora Basin is post-Lahontan only. The area of the present Mono 

 Basin is 675 square miles. With the Aurora Basin, the total is 770 square miles. 



THE OWENS BASIN. 



The Owens Valley occupies the central and largest portion of the trough just east 

 of the Sierra. Its general slope ia southward and it is occupied for most of its length 

 by the Owena River, which empties into Owena Lake at the southern extremity of 

 the valley. South of the lake is an alluvial divide only 166 feet above the present 

 surface of the lake. Tliis divide is apparently of some antiquity, but it is considered 

 practically certain that the lake overflowed it during the Lahontan period and dis- 

 charged southward into the Searles Basin described below. The independent history 

 of the Owens Basin is therefore comparatively short, and the considerable salinity of 

 Owena Lake acquirea unusual interest for the interpretation of the geochemical 

 history of the Great Basin. 



1 U. S. Geol. Sur., 8th Annual Report, Part I, pp. 261-394 (1889). 



