NEOCENE RIVERS OF THE SIERRA NEVADA. 
By Waldemar Lindgren. 
During the geological mapping of the gold belt of the Sierra Nevada 
much information was gathered relating to the gravel mines, and 
attempts were made to reconstruct the drainage systems of the Neo- 
cene rivers, now represented by detached masses of lava-covered 
detritus, generally at high elevations above the present drainage 
level. Many of these deposits were described in the texts of the 
folios of the gold belt by Mr. II. W. Turner or myself. A very brief 
review of the gravel mines and the channels of the central gold- 
bearing region was given in the bulletin of the Geological Society 
of America.^ None of these publications, however, does full justice to 
the important and interesting problem of the Neocene stream gravels 
of the Sierra Nevada, a subject fascinating alike from the economic 
and the scientific side. Whitney's monograph on this same subject, 
while containing an enormous amount of valuable observations, is 
out of date, because of the careful geological mapping by which the 
country has been covered since that volume was written. 
It seemed advisable, therefore, to collect in one publication the 
principal facts and conclusions regarding the Neocene gravels. Some 
supplementary work was found to be necessary, and four months of 
the season of 1901 — from the beginning of July to the end of October — 
were devoted to the study of the gravels in Butte, Placer, Calaveras, 
and Tuolumne counties. In this work I was assisted by Mr. J. M. 
Boutwell, who made a special reexamination of the Forest Hill divide 
in Placer County. About one month of the summer of 1902 was also 
given to a reexamination of certain deposits in the same county. 
The data which have been brought together are very voluminous, 
and their compilation has necessarily been delayed by the pressure 
of other work, but it is hoped will be finished during the present 
year. It is intended to review briefly the present state of this min 
ing industry, its probable future, its production, and the methods of 
mining peculiar to it. The structure of the Sierra Nevada will be 
described, and some attention will be devoted to the interesting 
a Lindgren, W., Bull. Geol. Soc. Am., Vol. IV, 1893, pp. 257- 
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