256 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



creek, and gorge with gorge, so that then when the water leaves the margin 

 of the rocky mass it is always united into a comparatively small number 

 of streams, and it is by these that the entire volume of detritus is discharged. 

 About the mouth of each gorge a symmetric heap of alluvium is produced, 

 a conical mass, of low slope, descending equally in all directions from the 

 point of issue, and the base of each mountain exhibits a series of such allu- 

 vial cones, each with its apex at the mouth of a gorge, and with its broad 

 base resting upon the adjacent plain or valley. Rarely these cones stand 

 so far apart as to be completely individual and distinct, but usually the 

 parent gorges are so thickly set along the mountain front that the cones are 

 more or less united, and give to the contours of the mountain base a scal- 

 loped outline." 



In the Lahontan basin alluvial cones are to be seen everywhere about 

 the bases of the mountains, and were evidently a conspicuous feature in 

 the pre-Lahontan topography, as is abundantly illustrated by the fact that 

 the shore lines of the former lake are traceable for hundreds of miles on 

 alluvial slopes of great magnitude. This is particularly noticeable in the 

 northern portion of the basin where the lake was generally shallow, and 

 may be observed especially in the Humboldt and Quinn River valleys and 

 about the bases of the Slumbering Hills. The same phenomenon is also 

 conspicuous about the borders of the Carson Desert and in Buffalo Spring, 

 Alkali and Mason valleys, as well as at many places on the borders of 

 Walker Lake Valley. These alluvial slopes streaming down from the 

 mountains to a horizon far below the old beach lines, bear evidence that 

 the valleys were deeply filled with alluvium before they were occupied by 

 the Quaternary lake. Since many of these basins never overflowed, it is 

 evident that the alluvial slopes were formed during a time of desiccation 

 when evaporation equaled or exceeded precipitation. If this had not been 

 the case, it is manifest that lakes would have been formed and the debris 

 filling their basins arranged in stratified beds or built into bars and em- 

 bankments. A large number of valleys in the northern part of the Great 

 Basin which held inclosed Quaternary lakes have been explored, and in 

 each instance the same relation of shore terraces to previously formed 

 alluvial slopes has been observed It is therefore considered as proven 



