282 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 



in the same region will be found described briefly in the Fourth Annual 

 Report of the U. S. Geological Survey.*^ 



From the studies of the recent displacements of the Lahontan basin 

 which we have been enabled to make, it seems safe to conclude that these 

 orographic movements are but the continuation of a series which had its 

 beginning long previous to the Quaternary. These movements were in 

 progress during the existence of Lake Lahontan, as indicated by sloping 

 terraces, and no less plainly by tufa deposits along lines of fracture. As 

 shown above, the evidence that these movements have been in progress in 

 very recent times is abundant. The character of the phenomena is such 

 that it is impossible to resist the conclusion that the forces which produced 

 the results described are still in action. 



Whether the faults have been formed gradually without any marked 

 disturbance, or whether they have been paroxysmal, is not definitely 

 known. That earthquakes are felt from time to time in various parts of 

 the Great Basin, and the results produced by the Owen's Valley earth- 

 quake of 1872, tend to the conclusion that the orographic movements have 

 been paroxysmal in their nature. 



The Owen's Valley earthquake, it will be remembered, resulted in the 

 formation of a false scarp of the same character as those we have been 

 describing, which may be traced for a number of miles As reported by 

 Mr. Gilbert, who recently visited Owen's Valley, the main scarp produced in 

 1872 varies from 10 to 20 feet in height, hades eastward at a high angle, 

 and agrees in all its features with the similar scarps observed throughout the 

 Great Basin. This is apparently the latest slip in the great Sierra Nevada 

 displacement. 



In the case of all the recent faults of the Great Basin thus far exam- 

 ined, the movement has been nearly vertical, and but slight crumpling or 

 contortion of the adjacent strata has taken place. 



A general view of the phenomena presented suggests that in the 

 majority of instances the blocks now forming the mountains have been 

 raised vertically, while those beneath the valleys remained nearly undis- 

 turbed. This hypothesis cannot be sustained by direct proof, however, 



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