THE NATURE OF THE LATER DEFORMATIONS IN 
CERTAIN RANGES OF THE GREAT BASIN 
CHARLES LAURENCE BAKER 
The department of paleontology of the University of Cali- 
fornia has lately made three expeditions into different regions of 
the southwestern part of the Great Basin with the main purpose 
of collecting Tertiary mammalian fossils. Incidentally a con- 
siderable body of new facts relative to the deformational and 
physiographic history of the later Cenozoic have been gathered, 
and a brief summary of some of the more important of these is 
here presented. No greater degree of accuracy than that implied 
by a rapid reconnaissance can be claimed for these statements. 
They apply to the following sections: the southern Sierra Nevada 
from the vicinity of Mono Lake southward to a point beyond 
Tehachapi Pass; the Black Mountain Range; the Calico Moun- 
tains of the central Mohave Desert; the El Paso Mountains, a 
short low range running en echelon with the southern Sierra Nevada 
southwest of Walker Pass; the northern White Mountain or 
Inyo Range on the boundary line between Nevada and California; 
the northern Silver Peak Range; the northern Pilot Range; the 
southern Gabbs Valley Range; the Cedar Mountain Range west 
and northwest of Tonopah, in central western Nevada; and the 
intervening basins. 
The main tentative conclusion reached is that the conception of 
the extensive development of normal or gravity block faults of great 
displacement originally advanced by Russell and LeConte, and sub- 
sequently adopted by King, is fundamentally erroneous so far as 
this portion of the Basin Range province is concerned. In the 
opinion of the writer the Basin Ranges are really mountains of 
tangential compression. The evidence for this view is both 
structural and physiographic. The block faults, first described 
by Gilbert, can apparently be explained in considerable propor- 
tion quite as well as ‘‘upthrusts’—in the sense in which this 
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