18 BULLETIN 54, U. S. DEPARTMENT OF AGRICULTURE. 
higher. The former is alluvial and is believed to be recent. The latter is mapped by 
King as basalt. It is very probable that the early drainage of this group was northward 
into the Humboldt, and their interest to the present inquiry, accordingly, disappears. 
The total area of the group is 1,075 square miles. 
THE WALKER BASIN. 
There remains for discussion only this one division of the great Lahontan water body. 
It lies south of the Lahontan body proper, and consists essentially of two north and - 
south troughs lying on either side of the Walker Range. Rising in the Sierras, the 
Walker River flows northward through the western trough, around the north end of the 
Walker Range, and into the deeper eastern trough, the deepest depressions of which 
contain the present Walker Lake. Structurally, the affiliations of the Walker trough 
are much more with the isolated trough valleys to the east and south than with the 
valleys of the main Lahontan area. Only the accident of a low pass to the north enabled 
the early Walker Lake to overflow and establish a connection with Lake Lahontan. 
This connection was never a deep one, and the Walker body was the first of the main 
Lahontan water bodies to become separated when the lake began to fall. Itis probable 
that it continued for a time to overflow into Lahontan, but advancing desiccation must 
have put an early end to this, and the independent history of the Walker Basin is 
probably a fairly long one. 
Like the Truckee and the Carson, the Walker River has been able to keep its stream 
fairly vigorous and its main channel fairly clear, but numerous local playas and ‘‘alkali’”’ 
flats have been formed in the tributary valleys. Most of these are too local and 
recent to deserve especial notice. The most important is the chain of two basins north 
of the Gillis Range and now separated from the Walker Valley and from each other by 
low alluvial divides. Several similar basins border the Walker River in its northward 
course through the western trough. 
Along the west Walker River (a branch of the main river) are several basins which 
are interesting because of their less usual origin, though no more important to the present 
inquiry. It seems that the upper course of this river was once a series of lake basins 
apparently of structural origin. In the course of time the river cut narrow canyons 
through the walls of these basins and drained the lakes. But, this done, the river has 
sometimes deserted the axis of the basins for a channel along a traversing delta of its 
own building, leaving to one side or the other depressions still below the river or its 
outlet. With complete desiccation these depressions have become undrained basins 
with central playas of usual type. This appears to be the history of the playa in the 
north end of Smith Valley. The playasand alkali lakes of the Antelope Valley probably 
owe their origin in part to similar processes, though these processes have been much 
complicated by fan-building and alluvial deposition. 
The area of the Walker Basin at the present time is approximately 3,200 square miles. 
Including all the areas once tributary to it but now cut off by damming or stream decay, 
it covers 3,850 square miles. Walker Lake has a present area of 104 square miles, but 
this has varied greatly in the recent past, as is attested by the extensive and complete 
system of old-shore lines which surrounds it. 
THE BONNEVILLE BASIN AND ITS TRIBUTARIES. 
Though somewhat larger than the Lahontan Basin, the Bonneville 
Basin is much more nearly a unit. In Lahontan time it received the 
drainage of all the inclosed region east of the Bonneville-Lahontan 
divide, its deepest portion being occupied by the Great Lake Bonne- 
ville, with an area at its highest stage of nearly 20,000 square miles. 
