662 CHARLES R. KEYES 
perfectly inexplicable on any postulation of normal stream-action. It 
is, moreover, nowhere more strikingly shown than in the Death 
Valley district; and it is clearly recognizable throughout the desert 
country. Nor is this genetic independence of development satis- 
factorily explained on the basis of tectonics. The profile below, 
through the Death Valley region, displays these relationships of 
several adjoining intermont plains. 
In neighboring valleys of the dry region the local level below 
which eolian erosion cannot go seems to be sharply determined by 
lines where the ground-water surface reaches sky. It is much the 
same as when in a humid land a barrier to surface drainage fixes 
for a time the local base-level.. Those local geologic structures which 
Arcus RANGE 
PARAMINT RANGE 
8000' GRAPEVINE RANGE 
6000" 
AmRAGOSA 
VALLEY 
2500! 
DEATH 
VALLEY 
Nes S00 af cyt peso eh eee 
IEA REVELL TS Beh ee eee 
Fic. 1.—Hypsometric Independence of Intermont Valleys of the Arid Region 
control ground-water level may be slightly or very different in neigh- 
boring intermont areas; but so long as in the one the level of phreatic 
waters comes to the surface of the ground and in another it does not, 
the effects of differential deflation will be very marked and plains of 
the first-mentioned class will remain high above the other, notwith- 
standing the fact that the two appear to be directly connected so far 
as their surface drainages are concerned. 
Death Valley and the Imperial Valley, before the Salton Sea grew 
so large through the incursion of the waters of the Colorado River, 
are good illustrations of this phenomenon. In the case of the first- 
mentioned of these valleys especially, now about 500 feet below sea- 
level, it is not at all likely that the salt lake which occupies a portion 
of its area is so much due to the desiccation of surface waters drained 
into the depression from all sides as it is to the fact that the valley is 
excavated by deflation down to a level where it could go no farther on 
