4G 



GEOLOGICAL HISTORY OP LAKE LAHONIAN. 



end of Mason Valley the river bends abruptly southward, at the SExme 

 time increasing the depth of its channel, which soon becomes a canon 

 through lake-beds similar to the ones carved by the Humboldt and the 

 Truckee. Captain Simpson reports the Walker River near its mouth to 

 have been about 100 yards wide and from G to 10 feet deep on June 7, 

 1859.-' A measurement of the volume of the river about 3 miles from 

 its mouth, June 4, 1881, gave 400 cubic feet per second as the rate of flow. 

 In October of the following year its bed was dry, and little, if any, water 

 reached the lake from this source. This decrease during the dry season is 

 evidently due in a great measure to the extensive use of its waters for irri- 

 gation in Mason Valley. As a rough average, the data at hand being 

 inexact, I have assumed 200 cubic feet per second, or 700,000,000 cubic 

 jards annually, as the approximate discharge. An analysis of a sample of 

 water collected October, 1882, at a point just below where the main branches 

 of the river unite, is reported by Prof F. W. Clarke, as follows: 



CoDSlituents. 



Silica (SiOa) 



Calcium (Ca) 



Magnesium (Mg) 



rotassium (K) 



Sodinm (Na) 



Chlorino (Clt 



iSulphuiic acid (SO4) . 



Carlxinii- acid (COi) by difFerence . 

 Total 



Constituents. 



Silica (3iOz) . 



Calcium carbonate (CaCOi) 



Magnesium carbonate (ilgCOa) 



Sod iura chloride ( XaCl) 



Sodium auli)hate ( Na^SOj) 



Sodium carbonate (NazCOa) 



Total (99.39 per cent, accounted 

 for) 



Probable com- 

 bination (in 

 grammes per 

 liter). 



0. 0225 

 0. 0570 

 0.0133 

 0. 0216 

 0. 0421 

 0. 0224 



The measurements of the volumes of the rivers of the Lahontan basin 

 at different seasons indicate the great fluctuations to which the drainage in 

 a desert country is subject. The rivers are flooded during the winter and 

 spring — which includes the rainy season, and also the time when the mount- 

 ain snows are melting most rapidly — and diminish greatly in volume during 

 the parched and arid summer months. The Truckee River is an excep 

 tion to this rule, as it is the overflow of a great reservoir. Lake Tahoe, 



I Exploratious AcrosB tbe Great Basin of Utah, Wasbingtou, D. C, 187G, p. 87. 



