18 BULLETIN 54, V. S. DEPAKTMENT OF AGKICULTURE. 



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. It is 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 playas and 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. 



i 



