44 



GEOLOGICAL HISTOEY OF LAKE LAHONTAN. 



as is shown by the fact that from Dayton to the Carson Desert it was occu- 

 pied by the waters of Lake Lahontan. During the existence of the lake 

 the valley became deeply filled with lake sediments and delta deposits, 

 which were re-excavated as the lake fell. The present gorge is the work 

 of the second period of excavation. The structure of the canon between 

 Churchill Valley and the Carson Desert is represented in the following ideal 

 section, which shows the older canon in volcanic rock partially filled with 

 lacustral sediment, and the second carved out of stratified lake-beds. 



Fig. 5. — Ideal croea-section of Carson River Caflon, Nevada. 



Measurements of the volume of the Carson River at Old Camp Church- 

 ill, July 1, 1881, gave between 450 and 500 cubic feet per second as the 

 volume of tlie stream ; in September, 1883, the discharge was less than half 

 this amount. 



The bifurcation of the Carson River after entering the Carson Desert 

 is represented on the accompanying map (Plate VII). For the history of 

 the changes that tlie river has undergone during the last few years I am 

 indebted to some of the early pioneers, who made this region their home. 

 Previous to 1862 it flowed into the Sovith Carson Lake, but there was an 

 abandoned channel branching from it and leading northward. During a 

 time of unusually high water in the spring of 1862 the river bifurcated, 

 the old channel was reoccupied, and a branch flowed to each lake. The 

 point at which the river divided is indicated on the map by the date 1862. 

 Previous to that time there was a "slough" connecting the North and South 

 Carson lakes through which the waters flowed northward. After the forking 

 of the stream tlie South lake was lowered so that it no longer overflowed, 

 and the water in the slough became stagnant. Another flood occurred in 

 the spring of 1867 or 1869, which caused the arm emptying into North 

 Carson Lake to brancli and send a stream eastward to the slough. The last- 



