80 AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
they extend high up towards the crest of the Sierra. He also explored the 
region about the South Fork of the American, and examined all the im- 
portant points in El Dorado County, especially the neighborhood of Placer- 
ville, as well as a considerable portion of El Dorado and Amador counties, as 
far south as the Mokelumne River. Nearly or quite all the hydraulic mining 
districts where any work was doing between that river and the North Fork 
of the American were examined by Mr. Goodyear during the course of the 
summer. The region north of the North Fork of the American, as far as the 
Middle Yuba, was assigned to Mr. A. Bowman, who took the field early in 
the spring of 1870. Professor W. H. Pettee joined him in July, and they 
together spent nearly all the remainder of the year in working out the 
geology, and mapping the detailed topography over the area indicated. 
From their surveys, aided by such information as could be obtained from the 
various gravel mining and ditch companies in the region, the map, which is 
appended to this volume, was compiled by Messrs. Hoffmann and Craven. 
This map, which is on a scale of one mile to the inch, extends over the area 
between the Middle Fork of the American and the Middle Yuba, embracing 
the most important hydraulic mining region of the State. The work of 
Messrs. Bowman and Pettee was supplemented on the north by surveys made 
for private companies by Mr. Hoffmann, so long chief topographer of the 
Geological Survey; the work thus introduced was especially important as 
including perhaps the most important of all the gravel deposits in the State, 
those between the South and Middle Yuba. A considerable number of ditch 
lines in the region surveyed are also laid down from information furnished 
by the various companies; also all the quartz and gravel mining claims 
which had, up to 1873, been patented or officially surveyed for the purpose 
of securing a patent under the United States laws are indicated upon this 
map.* 
In regard to the extension of the gravel ranges north of the Middle Yuba, 
our data are far from complete. The region was traversed at different times 
by various members of the Survey, but never systematically explored. This 
is especially true for the interesting district between the Middle Yuba and 
Slate Creek. Plumas County was explored by the writer in 1866; but here 
the gravels have by no means the importance which they possess farther south. 
* As the location of these claims is not a matter of scientific interest, it has not been considered neces- 
sary to have the map brought up to date in respect to the additional patents which have been issued 
since 1873. 
