412 SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 
man’s Creek, or both. The high spur of gravel on the east of the creek indicates that there 
was once a large body of gravel at this point. The ground is worked by a company, whose 
claim also covers the deep mass of tailings in the creek, which have come from the Alpha and 
Omega mines. Hydraulic mining can never be carried on here on a large scale, on account of 
lack of space for a dump. 
The Washington ridge, from Diamond Creek downwards as far, at least, as Nevada City, needs 
a re-examination. It will have to be carefully surveyed and mapped before anything decisive can 
be published in explanation of the geological problems which there present themselves in connection 
with the gravel and the capping of volcanic tufa. The tufa when first exposed to view in the 
digging of the ditches is usually hard and firm, but it changes rapidly under the action of the 
atmosphere. Slides of lava down the steep sides of the ridge are of frequent occurrence. At 
the head of Washington and Jefferson Creeks there are some unusually steep and precipitous walls 
of voleanic rock, -—the result of the rapid erosion. Efforts have been made to find high gravel 
under the lava of this ridge similar to those which have been referred to already in connection 
with the lava capping above Columbia Hill and Snow Point. I heard frequent mention made of j 
the Centennial claim, and of the tunnel which had there been driven in under the lava until gravel 
was struck. The claim is said to be near the head of Jefferson Creek, a quarter of a mile northerly 
from the ridge-road. I could not learn that the gravel found was in paying quantities, and I did 
not have the time to attempt any personal examination. 
The only other points on this ridge that I was able to visit in person were at and near Blue Tent 
and Sailor Flat. At the former place I was entertained by Mr. D. T. Hughes, at that time super- 
intendent of the Blue Tent mines, and at the latter by Mr. B. D. Chadwick and Mr. O. B. Camp- 
bell, two of the owners of the Sailor Flat mines. 
The map and sections on Plate O were prepared from documents at Mr. Hughes’s office. The 
Blue Tent property is owned by an English company, known as the Blue Tent Consolidated 
Hydraulic Gravel Mining Company. The Sailor Flat property lies to the east of the Blue Tent 
ground, near the forks of Sailor Flat and Last Chance ravines. A small claim intervening be- 
tween these two is owned by other persons. The gravel owned by the Blue Tent Company covers 
nearly five hundred acres, as will be seen by an inspection of the map, where the heavy lines are 
the boundary of the property. The broken line shows the boundary of the gravel, which extends 
both to the east and the west of the company’s ground. The Sailor Flat Company owns about 
360 acres of mining ground. JI did not see any map of the property, but Mr. Chadwick gave me 
the approximate bounding lines, as follows: an east and west line of 7,000 feet in length along the 
centre of the ridge ; a front line, also running east and west, of about 4,500 feet in length; and 
two side lines of about 3,000 feet each. 
The surface gravel is continuous over the Blue Tent and Sailor Flat grounds, and, for the greater 
portion of the area, it is of unknown depth. About twelve acres of bed-rock, according to my 
estimate, are exposed to view at Gopher Hill, at the northeasterly end of the property, overlooking 
the South Yuba River. A larger area than that is represented on the map as “ exposed bed-rock,” 
but some of the lower gravel and some of the gravel on the edges is still unwashed. The bed-rock 
at this point is slate, and it has a gradual pitch to the south under the gravel. I took an observation 
for altitude on the bed-rock, near the point marked “B” on the map, about a thousand feet back 
from the river bluff, and made it to be 2,483 feet, practically the same as at Grizzly Hill, on the 
opposite bank of the river, —a result which agrees very well with the hand-level observations. 
The two deposits were doubtless connected with each other before the erosion of the present cafion 
of the South Yuba. The only other observation for altitude that I took in this vicinity was near 
an exposure of rim-rock at the Sailor Flat mine, on the spur between Sailor Flat and Last Chance 
ravines, about three quarters of a mile to the southeast of Gopher Hill. Here the altitude was 
2,759 feet, — 276 feet higher than at the former point. There was no other exposure of bed-rock 
at which it seemed worth while to determine the altitude. At Sailor Flat the gravel has been 
removed for several hundred feet back towards the south from the point of which I took the 
