RECENT FAULTS. 270 



the contour of the lake bottom is indicated to some extent by the soundings 

 given on the map forming Plate XV. The lake is deepest in the immediate 

 vicinity of the fault line. 



It is probable that the direction taken by Walker River on leaving 

 Mason Valley was determined by orographic movement, as it does not fol- 

 low what appears to have been its natural course, but the character of this 

 change is difficult to describe. The former outlet of Mason Valley was 

 through a narrow gorge leading to the Carson River which it entered at a 

 point opposite the site of Camp Churchill. This would probably have been 

 the course taken by the stream when the waters of Lake Lahontan were 

 withdrawn for the last time, had not orographic movement caused a slight 

 change in the slope of the valley and thus deflected the river to tlie right. 

 This phenomenon will be better understood on consulting the acconipanj^ 

 ing pocket map, where the ancient channel leading from Mason Valley to 

 the Carson River is indicated. 



That portion of the great Sierra Nevada fault which defines the western 

 border of Carson and Eagle valleys has undergone a recent displacement 

 of from ten to thirty feet, as is shown by fresh scarps in earth and gravel, 

 and also by the outflow of heated waters at several localities. The recent 

 scarp in this instance has been followed all the way from near Carson City 

 to beyond Genoa; the full extent of the movement, however, far surpasses 

 these limits. 



The basin of Lake Tahoe is an orographic valley of the Great Basin 

 type, but is situated at a high altitude in the Sierra Nevada on the border 

 of the interior drainage area. With the exception of the hot springs at the 

 northern end of the lake, no evidence is known to the writer tending to 

 show that there has been recent orographic movement in its immediate 

 vicinity. 



The faults along the eastern base of the Pine Forest Mountains ; on 

 the western margin of the Black Rock range, from Black Rock point north- 

 ward, and at the northern base of the Harlequin Hills are all marked in 

 the topography of the country by recent scarps that seldom exceed twenty 

 feet in height. At numerous points along these lines of displacement 

 thermal springs come to the surface. 



