A GEOLOGIC RECONNAISSANCE IN SOUTHWESTERN 
NEVADA AND EASTERN CALIFORNIA. 
By Sydney H. Ball. 
HSTTRODTJCTIOlSr. 
FIELD WORK AND ACKNOWLEDGMENTS. 
The field work on which this bulletin is based covered a period 
lasting from June to December, inclusive, 1905. The geologic work 
was under the general supervision of Mr. F. L. Ransome, and was 
carried on simultaneously with the mapping of the topographic base 
by Messrs. R. H. Chapman and B. D. Stewart, 
The writer is fully conscious of the many inaccuracies of the 
geologic maj) herewith presented, but trusts that it may prove not 
only an aid to the prospector and miner, but a contribution to the 
geology of an intensely interesting region. Each day approximately 
45 square miles was mapped in an area of by no means simple geol- 
ogy, and in many localities the geologic mapping of necessity pre- 
ceded the topographic. No other region in the United States is so 
favorable to rapid mapping, since the exposures are unexcelled and 
the scant vegetation masks scarcely a geologic detail. The geology 
of the Paleozoic rocks is, hoAvever, difficult, partly on account of the 
lithologic similarity of many of the formations, but largely because 
these older rocks are in part hidden by mantles of Tertiary lavas and 
Recent gravels. In the text it has been the endeavor to distinguish 
clearly between observations made at close range and inferences 
.drawn with the aid of the field glass. The mapping of the outer 
poldfield hills and of the Pahute Mesa are particularly unsatisfactory. 
To Mr. F. L. Ransome the writer desires to express his apprecia- 
tion for general oversight and helpful criticism. Messrs. J. E. 
|Spurr, F. B. Weeks, W. H. Emmons, and G. H. Garrey have been 
freely consulted on various points of Nevada geology. Messrs. R. H. 
Chapman and B. D. Stewart and their assistants, Messrs. T. C. 
Spaulding, E. A. Childers, and S. G. Benedict, aided the work by 
[collecting in the field specimens of rocks from many points not vis- 
ited by the writer. Mr. Spaulding also furnished some photographs 
and determined the species of the desert flora. To Messrs. W. F. Ilil- 
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