TOPOGRAPHIC FEATURES OF THE DESERT BASINS. 39 
main uplift, that of thie, om Bormaading Mountains, but the trend is 
here northwest and southeast, instead of north and south. 
These trends of the basm boundary are paralleled by the troughs 
within it. In the northern part of this division are tour 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 Valley, and 
the fourth and last is that of the Amargosa Valley, 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 
River, though the Kane, Willard, 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 dramage of the Colorado 
River, being cut by alluvial divides in the same manner as the trough 
valleys 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 is southward and it is occupied for most of its length 
by the Owens River, which empties into Owens 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. This 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 
Owens Lake acquires unusual interest for the interpretation of the geochemical 
history of the Great Basin. 
1U.S. Geol. Sur., 8th Annual Report, Part I, pp. 261-394 (1889). 
