46 BULLETIN 54, U. S. DEPARTMENT OF AGRICULTURE. 



tliis elevation determiuiBg a water parting, wMcli is superficially alluvial but never- 

 theless quite ancient. This divide crosses the trough in the neighborhood of Wilburs 

 Well, located by the surveys of the General Land Office in township 3 north, range 

 5 east, San Bernardino base and meridian. West of this point the trough was once a 

 tributary of the Mojave, and now contains a series of playas due to tliis tributary's 

 decay. East of the divide the trough once drained to the Colorado River, but alluvial 

 damming has now cut it into a half dozen basins each independent and inclosed and 

 each with its typical playa. It has not been considered necessary to attempt the 

 delineation and study of each of these local basins in detail. The most important 

 are those of Mesquite, Dale, and Palen Lakes. The exact heights of the various 

 di^ddes are unknown, but all are believed to be recent and the basms they form are 

 thought to have belonged quite recently to the Colorado drainage and to have, there- 

 fore, slight importance to the present inquiry. The total area of present inclosed 

 drainage in this trough and east of the W^ilburs Well divide is 3,520 square miles. 



THE BRISTOL TROUGH. 



The second trough north of the San Bernardino Mountains is occupied by the basins 

 of Bristol, Cadiz, and Danby Lakes, the first receiving also the drainage of a high 

 valley running toward the northeast between the Providence and Piute (or Pahute) 

 Ranges. The exact interrelations of these lakes and their basins are not fully known, 

 but they are believed to be analogous to those of the trough last discussed, and to have 

 drained quite recently into the Colorado River. The divide between the westernmost 

 or Bristol Basin and the Mojave is the local uplift of Ash Hill and is believed to have 

 originated in connection with .a center of recent vulcanism a little to the west. This 

 di\dde, though of no considerable antiquity, is believed to be pre-Lahontan. The 

 only chance of importance of these basins to the present inquiry lies in the possibility 

 that one or more of them may have been inclosed longer than is assumed and may 

 have been an area of salt accumulation during a considerable period. The siu-veys 

 of the region are so few and so inaccurate that this possibility can not be absolutely 

 denied; though it is believed to be remote. Danby Lake is known to contain a 

 considerable deposit of common salt, but this is believed to be of recent and secondary 

 origin. The total area of the basins of all thi'ee lakes is approximately 4,150 square 

 miles. 



THE SALTON BASIN. 



South of and parallel to the San Bernardino Range is another 

 structural trough similar to those north of it but deeper, and open 

 southward to the Gulf of Cahfornia. Tliis trough is now cut off 

 from the Gulf by a low divide of alluvial material and its deepest 

 depression is occupied by the Salton Sea, the sui'face of which is over 

 200 feet below sea level. W. P. Blake, who made the first scientific 

 examination of the basin ^ and discovered its negative elevation, 

 concluded that the trough had once contained an arm of the sea 

 and had been cut off by the gradual out-building of the delta of the 

 Colorado River from the eastern shore. The delta having been built 

 above the water level, the river might have flowed northward into 

 the basin or southward into the Gulf. As a matter of fact it has 

 done both. Being an alluvial river of very variable bed, it has flowed 

 alternately to the basin and to the Gulf, probably many times in 

 each direction. The present Salton Sea was created by an accidental 



1 PaciOc Railway Uex>orts, Vol. .5 (IS.jG). 



