278 GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 



has increased its displacement fully fifty feet since the evaporation of the 

 Quaternary lake. 



The hot springs at Hot Springs Station, on the Central Pacific Rail- 

 road, occur on a line of recent displacement, which may be followed for a 

 few miles, both north and south, from the present site of the springs. De- 

 posits of extinct springs may be seen for a mile or moi'e north of the present 

 point of outflow, indicating that former openings, through which the springs 

 rose, have been filled by calcareous deposits, thus compelling the waters to 

 find other points of egress along the line of fracture. 



The recent fault on the east side of the Carson Desert is marked by a 

 low scarp in alluvium, and a change in the drainage where the displace- 

 ment crosses Alkali Valley. East of Borax Springs, situated in Alkali 

 Valley on the line of fracture, the slope of the desert surface is eastward, 

 and conducts the drainage to the end of the valley where a lake of brine is 

 formed, which on evaporating leaves a deposit of salt of economic import- 

 ance. Alkali Valley is bordered on all sides by precipitous mountains, 

 excepting where it opens into the Carson Desert, and formed a deep bay 

 during the existence of Lake Lahontan. In passing from the Carson Desert 

 into Alkali Valley no change in the nearly level desert surface is noticeable 

 until the line of faulting is reached; the plain then inclines gently eastward 

 as we have described. It is evident that this inclination of the desert surface 

 has taken place in post-Lahontau times, and is due to a slight tilting of the 

 orographic block on which Alkali Valley is located. 



The course of the fault indicated on Plate XLIV, as crossing the north- 

 ern border of Mason Valley, is rendered conspicuous in the topography of 

 the valley bottom by a scarp from ten to twenty feet high in lacustral marls 

 and clays, and by numerous thermal springs. This is probably a continu- 

 ation or a branch of a displacement in Walker River Valley which presents 

 a section of Lahontan sediments fully 150 feet high. In common with the 

 majority of the recent displacement of northern Nevada, both ends of this 

 fault are obscure and indeterminable. 



What is probably a continuation of the series of disturbances observed 

 in Mason Valley is indicated by a recent scarp along the east base of the 

 Wassuck or Walker Lake range. The influence of this displacement on 



