32 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



River. Tlie water in this t'liamiel during the highest stage of Lake Lahontan 

 was 350 to 380 feet deep. The equally narrow strait connecting the P^ast 

 and West bodies at the south is now occupied by the lower portion of the 

 Truckee Iviver in its course between Wadsworth and Pyramid Lake. 



On Plate V, the depth of the Avater during the highest stage of Lake 

 Lahontan is given in feet. These determinations are mostly from aneroid 

 measurements, and show the lake to have been about 500 feet deep over 

 the Carson Desert, becoming shallow in its extension up the Humboldt 

 Valley. On the Black Rock and Smoke Creek deserts the depth was from 

 500 to 524 feet. The deepest sounding in the old lake, however, as already 

 stated, was at the present site of Pyramid Lake, where the depth was 886 

 feet. 



- While the various valleys composing the basin of Lake Lahontan are 

 orographic in their character, the canons of inflowing streams are largely 

 due to erosion. All the rivers, as well as the smaller creeks that were 

 tributary to the lake, flowed in deeply cut canons, many of which were 

 occupied for a long distance by the waters of the lake when it reached its 

 maximum extent. These canons will be more fully noticed in connection 

 with the description of the Lahontan lake beds. 



Lahontan was intermediate in area between Lake Erie and Lake 

 Ontario, Init was far less systematic in outline than either; in fact its 

 boundaries were more irregular than any other lake, recent or fossil, that 

 has been ex})lored. As shown on the frontispiece, it was smaller than Lake 

 lionneville, and ranks as second in size of the Quaternary lakes of the Great 

 Basin. 



QUESTION OF OUTLET. 



hi stii(K'ing the records of an ancient lake, one of the first questions to 

 which it is desirable to iind an answer is whether it overflowed or not; and 

 if it did find an outlet, what are the characteristics of the channel of dis- 

 cliarge. The importance of determining the )iature of the channel of overflow 

 of a fossil lake is illustrated in the case of Lake Boinieville, which, as is well 

 known from Mr. Grilbert's investigations, rose until it overflowed at Ived-Rock 



