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 



on 



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 connecti 

 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 volcanic 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 

 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. 0. B. Camp- 

 bell, two of the owners of the Sailor Flat mines. 



The map and sections on Plate 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 arc 

 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 



I 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, overlookin 

 the South Yuba Biver. 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 



360 acres of mining ground. 



n- 



f 



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 canon 

 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 



