TOPOGRAPHIC FEATURES OF THE DESERT BASINS. 538 
in a group of small and variable lakes. The inclosed condition of the valley is un- 
doubtedly very recent and due only to stream decay. The area of the present basin 
is about 2,800 square miles. 
THE RED DESERT BASIN. 
The Red Desert Basin, or group of basins, lies in south-central Wyoming, on the very 
crest of the Rocky Mountains, occupying a broad plain bordered on three sides by 
mountain ranges but essentially open toward the south. Atatimeby no means remote 
thissouthern divide was nonexistent and the basin drained, probably freely but at least 
by overflow, into the Little Snake River and thence to the Colorado. The present 
barrier is a series of low divides which are superficially alluvial and probably entirely 
so. The basin is by no means a unit but is cut by alluvial or structural divides into 
a complex series of smaller basins each with its playa and its greater or lesser drainage. 
The past and present relations of these basins are not known in detail, but it is im- 
probable that their discharge ever concentrated in a single basin or a single channel 
of escape. The region is more a decayed drainage system than a single basin. 
None of these basins is ancient, and none would have any importance were it not 
for the fact that part of the western slope of the area is formed by the Leucite Hills, 
a zone of volcanic activity in which are large masses of leucitic rocks containing con- 
siderable proportions of potash.1 How fully the drainage of these hills has been 
localized and retained can not be determined from present data. The writer inclines 
to the opinion that both retention and concentration have been comparatively slight, 
but the evidence is far from conclusive, and the region can not be disregarded. It 
should be noted that the presence of extensive deposits of sodium salts in the basins 
of the Red Desert and in other small basins both west and east of it is no proof of 
long-continued concentration. The shales and sandstones which make up the greater 
portion of the areas tributary to these basins contain large quantities of occluded 
sodium salts, which rapidly find their way into the drainage and to the places where 
it concentrates. ‘ 
West of the Red Desert and on the westward slope of the Leucite Hills are several 
small and local basins now without overflow and which share the topography and 
geochemical characteristics of the western part of the Red Desert proper. 
The total area of the Red Desert Basin is approximately 3,600 square miles, but it 
is apparent from the above discussion that importance lies not in the total area, but 
in the areas and topographies of the various subsidiary basins and in what propor 
tion of leucitic country chanced to be tributary to each. These facts can not be 
determined from the information now available. 
THE GREAT VALLEY OF CALIFORNIA. 
Through the heart of California, between the Sierra Nevada and 
the Coast Range, runs a great filled trough which differs from the 
“basin troughs” east of the Sierra only in its greater size and in the 
fact that its western wall is breached by the Golden Gate, giving free 
egress to the sea. Southward through the north end of this valley 
flows the Sacramento River, and northward from the south end comes 
the San Joaquin, both rivers uniting to form the Straits of Suisan 
and entering the sea through San Francisco Bay and the Golden 
Gate. In essence both the Sacramento and San Joaquin Valleys are 
regions of free seaward drainage, but rainfall is low, and is insufficient 
to keep the valleys entirely clear. Local playas and ‘‘alkali” spots. 
1 See Schultz and Cross, U. S. Geol. Sur., Bull. 512 (1912). 
