142 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



displacements is usually indicated by fresh scarps in lacustral clays and 

 gravels. Since the desiccation of Lake Lahontan there has been consider- 

 able movement along- some of these ancient lines of fracture, and the La- 

 hontan beaches and terraces no longer retain their normal position, but in 

 places have been carried far above the horizon which they originally occupied. 

 If we consider the crest of the gravel embankment separating Walker Lake 

 Valley from the valley occupied by Walker River as approximately the 

 original level of the Lahontan beach, we find that the eastern end of the 

 structure, as determined by Mr. McGee, is now fully 200 feet above its 

 original position, as indicated at x', Plate XXVIII. The only explanation of 

 this phenomenon the writer can offer is that the fault following the eastern 

 border of the valley has increased its displacement in post-Lahontan times 

 and carried the shoreward portion of the bar above its normal position. 

 Similar disturbances may be seen in the northern part of the same valley, 

 where a post-Lahontan fault occurs on each side of the basin exposing char- 

 acteristic sections of Lahontan sediments. The altitude of the beach on 

 the eastern side of the valley is indicated at x, Plate XXVIII. In the bot- 

 tom of the valley and near the northern end, the strata are arched as indi- 

 cated in the generalized section. From the limited section open to exami- 

 nation, this seems to be a variable anticlinal, and, if so, it is the only post- 

 Lahontan arch of this nature that has been observed. The movements 

 that produced the disturbances in the northern part of the Walker River 

 Valley are connected with the recent displacements to be seen in the vicin- 

 ity of the hot springs in Mason Valley, and are so indicated on Plate XLIV. 



Local faults affecting the Lahontan sediments are of frequent occur- 

 rence, especially in the lower portion of the Walker River Valley; the throw of 

 these displacements is seldom over 40 or 50 feet, and they have caused but 

 little change in the topography of the valley. They are of different dates, 

 as is illustrated by figures A and B, Plate XXVIII ; in the former, the dis- 

 placement took place previous to the deposition of the medial gravels; and 

 in the latter, after the upper clays had been deposited. 



We have described the orographic movements in this region in some- 

 what general terms, for the reason that it is difficult to describe the facts on 



