MOHAWK LAKE BEDS. 
405 
main faulting must have occurred before the existence of the 
so-called Pliocene lake, which, on the grounds before given, 
may be supposed to have existed. 
Professor Le Conte studied the main fault scarp where it 
is at its maximum—that is, from Lake Mono south—but, so 
far as I know, has given no proof of so great a displacement 
as he indicates. The Sierra Nevada is thought to have been 
reduced to a base level of erosion during Tertiary time, and 
to have had an elevation not much, if any, greater than that 
of the great basin at the time of the displacement along 
Lake Mono and Owen’s Lake. But while there is evidence of 
the river channels having had a very moderate grade during 
Tertiary time in the more northern part of the Sierra, so far 
as I know no evidence has been adduced to show that the 
Sierra Nevada did not constitute a mountain range during 
all of Tertiary time in the region where it is now highest, 
viz., to the west of Owen’s Lake. No extensive gravel de¬ 
posits, showing ancient rivers flowing at a moderate grade, 
have, to my knowledge, been found there, and it remains for 
the future geological explorer in that region to get evidence 
that may decide the question- 
The general topography of the country indicates that the 
amount of displacement along the main fault scarp is much 
less in the region to the north of Lake Tahoe than from 
there south. Bearing on this point are some facts which I 
will now present. Referring again to Mr. Diller’s orographic 
blocks as set forth in Bull. No. 33, U. S. G. S., there is evi¬ 
dence of an old river channel that originated as far south, 
at least, as Haskell Peak, which is south of Mohawk Valley, 
and flowed in a course a little west of north across all three 
of these blocks. If future investigations substantiate the 
course of this river as above it can be certainly shown that a 
differential elevation or subsidence of the land on opposite 
sides of the fault line of the Mohawk Valley of perhaps a 
thousand feet has taken place, but it will be equally certain 
that this displacement took place previous to the deposit of 
the Mohawk lake beds, even the oldest, and after the deposit 
