262 The American Geologist. — May, 1902, 
playas or dry beds of lakes over which a thin sheet of water 
frequent!y spreads after a rain. 
In formér times, a large part of the Great basin was occu- 
pied by lakes of which the present lakes such as Great 
' Salt lake, Pyramid lake and Walker lake are merely fesiduals. 
It is, therefore, certain that in the past the climate of the reg- 
ion was much more humid than it is at present. This is well 
exemplified in Esmeralda county. In Miocene time, the area 
now covered by Clayton valley, the south end of Big Smoky 
valley, the north part of Silver Peak range and Columbus 
valley was the basin of a fresh-water lake, a description of 
which may be found in the 21st Annual Report of the United 
States Geological Survey.* 
In later time a Pleistocene lake covered much of north- 
ern and western Nevada. This is known as Lake Lahontan,+ 
and a south arm of this lake extended into Esmeralda county, 
covering the basin of Walker lake. The terraces of this an- 
cient lake may be plainly seen on the west side of Walker lake 
at the base of the Wassuck range. The latter is now about 25 
miles long and 4 and 5-10 miles wide. Formerly it extended 
south to the east of Hawthorne, at one point being only about 
half a mile from the present town site. 
Geology. 
In no part of the world can geological field work be done to 
better advantage than in the Great Basin. Except in those areas 
which are to be sure very extensive, that are covered with 
Pleistocene and Recent deposits, the rocks are almost every- 
where finely exposed, there being no soil or a very thin soil. 
In the western part of the Great Basin there are representa- 
tives of a large portion of the sedimentary series from the 
oldest Cambrian to the Recent. It is even possible that Ar- 
chean rocks exist here. Perhaps the greatest break in the ser- 
ies is in Cretaceous time, sediments of this period being thus 
far not reported. Beds of marine origin later than the Juras- 
sic are unknown in western Nevada, so that it is probable that 
this part of the Great Basin has been a land mass since the 
* The Esmeralda formation, a tresh-water lake deposit by H. W. Turner 
with a description of the fossil plants by F. H. Knowlton, and of a fossil fish, 
by F. A. Lucas, Twenty-first Ann, Report, U. S. Geol. Survey, pt. ii. pp. 191- 
226, pis. 24-31. 
+ For a more extended account of this lake see I. C. Russell, 3rd Annual 
Report, U.S. Geological Survey, 1883, aud Monograph xi, 1885. 
