GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



BY ISRAEL C. EUSSEIiL. 



ABSTRACT OF MONOGRAPH. 



The present volume records the history of a large lake which flooded 

 a number of the valleys of northwestern Nevada at a very recent geolog- 

 ical date, but has now passed away. This ancient water-body is known as 

 Lake Lahontan — named in honor of Baron La Hontan, one of the early 

 explorers of the headwaters of the Mississippi — and was the complement of 

 Lake Bonneville. The former, situated mostly within the area now form- 

 ing the State of Nevada, filled a depression along the western border of 

 the Great Basin at the base of the Sieri'a Nevada; the latter, embraced 

 almost entirely in the present Territory of Utah, occupied a corresponding 

 position on the east side of the Great Basin, at the foot of the Wasatch 

 Mountains. The hydrographic basins of these two water-bodies embraced 

 the entire width of the Great Basin in latitude 41°. Lake Bonneville was 

 10,750 square miles in area, and had a maximum depth of about 1, 000 feet. 

 Lake Lahontan covered H,422 square miles of surface, and in the deepest 

 part, the present site of Pyramid Lake, was 886 feet in depth. The ancient 

 lake of Utah overflowed northward and cut down its channel of discharge 

 370 feet. The ancient lake of Nevada did not overflow. Each of these 

 lakes had two high- water stages, separated by a time of desiccation. In 



the Lahontan Basin, as in the Bonneville, the first great rise was preceded 



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