46 BULLETIN 54, U. S. DEPARTMENT OF AGRICULTURE. 
this elevation determining a water parting, which 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 oncea 
tributary of the Mojave, and now contains a series of playas due to this 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 
divides are unknown, but all are believed to be recent and the basins 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 Wilburs 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 
divide, 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 surveys 
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 three 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 California. This 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 surface 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 Pacific Railway Reports, Vol. 5 (1856). 
