

L 



196 



THE AUKIFEROUS GRAVELS OE THE SIERRA NEVADA. 



intermingled with others of granite and metamorphic rocks. The thickness 

 of the mass is nearly 200 feet. Tunnels run under it, and shafts sunk from 

 the upper surface - — to but little depth, however — seem to have developed 

 nothing of value. 



Subdivision IV. — The Begion North of the SouTn Yuba River. 



§ 1. The Divide between the South and Middle Yuba Rivers. 



The intention of the writer of this volume was to have the hydraulic 

 mining region north of the South Yuba River surveyed with great care ; but 

 circumstances, to which allusion has already been made in the Preface of 



i 



this work, rendered this impossible. Several of the most important localities 

 in the district in question were visited at various times during the continu- 

 ance of the Geological Survey, either by the writer himself or by some one 

 of his assistants ; but most of these examinations, which were not detailed 

 and systematic, were made before the hydraulic mines in this extremely in- 

 teresting and important region had attained anything like their present 

 development and importance. Mr. C. F. Hoffmann, as already mentioned, 

 made special surveys in this district, for private parties, which were utilized 

 in preparing the large map appended to this volume, and to which reference 

 may be made in studying any portion of the gravel region from the Middle 



■ 



Yuba, as far south as Michigan Bluffs. 



Parties not connected with the Geological Survey have published impor- 

 tant documents in regard to the gravel deposits between the South and Mid- 

 dle Yuba, and their work will be made use of to some extent in preparing 

 the following pages* 



* The most important of these is a Report of James D. Hague, entitled "The Water and Gravel Min- 

 ing Properties belonging to the Eureka Lake and Yuba Canal Company and to M. Zellcrback, Esq.," and 

 dated December 22, 1876. Mr. A. J. Bowie, Jr., also gives valuable information, statistical and otherwise, 

 in regard to the region in question, in his " Hydraulic Mining in California," published in Volume VI. 

 of the Transactions of the American Institute of Mining Engineers, dated 1878. In the Fifth, Sixth, and 

 Seventh Reports of the United States Commissioner of Mining Statistics, for the years 1873 - 1875, will 

 be found various statements of value in regard to the mines of Nevada County, collected and compiled 

 by Mr. W. A. Skidmore. It may be stated, however, that it is the intention of the author of this volume 

 to procure additional information in regard to the region, north of the South Yuba, which will be pub- 

 lished either in the form of an appendix or supplementary chapter, as a portion of the present work ; or 

 in some other form, so that the important results which have been attained in the development of the 

 hydraulic mining interests in Nevada and Sierra counties during the years since the stoppage of tin- Geo- 

 logical Survey shall be placed before the public, in connection with these observations of earlier date. 



