480 SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 
Flat, also, the connection between the rest of the mountain and the Sugar Loaf has been broken, and 
it is possible that a detached mass of lava remains between the forks of Schermer’s Ravine. With 
these exceptions, the basaltic layer appears to be continuous and unbroken. At its highest point, 
the Sugar Loaf just mentioned, the mountain reaches an altitude of 1,500 feet above the level of 
the Feather River at Oroville. The top of the mountain has a gentle, uniform grade to the south- 
west of about one hundred feet to the mile. The thickness of the basalt is from one hundred to 
one hundred and fifty feet, or possibly a little more in some places. Had it been practicable for 
me to make precise measurements of the height of the bluff at a large number of points on all sides 
of the mountain, it is possible that a greater variation from uniformity of thickness than is indi- 
eated above might have been detected ; still it cannot be far from correct to say that the under 
surface of the basalt, or the surface of the material upon which the basalt now rests and over which 
one hundred feet to the mile —as the present upper 
it originally flowed, has nearly the same grade 
surface of the mountain. This naturally leads to the inquiry, What is the character of the under- 
lying material? The question cannot be answered completely, for no openings have been made, 
no shafts have been sunk down through the basalt to lay bare what is there concealed ; the only 
way of approaching a solution to the question is to examine with care the material at the base of 
the bluff, or within a short distance of the base, at as many points as possible. Such an examina- 
tion, however, as is here contemplated is not easy to make. At the base of the bluff the large 
accumulations of broken rock and débris pretty effectually conceal all underlying rock from view. 
At the best, it will be only here and there that really satisfactory information can be obtained. 
The number of my own observations which bear directly upon this question is small, —so small, 
indeed, that it will not be worth while to pursue this branch of the inquiry any further, except as 
it comes up incidentally in connection with the descriptions of the different places visited. 
At the north end of Table Mountain there is an extensive deposit of gravel near Cherokee Flat, 
which in many particulars is one of the most interesting deposits that I am acquainted with in 
the State. Owing to its comparatively elevated position with respect to the surrounding country, 
unusual outlays have had to be made, and unusual engineering devices resorted to, in order to 
secure a permanent and ample supply of water for hydraulic purposes. In the earlier days of 
mining in California this ground could only be worked on a very small scale, and during the rainy 
season. In the year 1870 a pipe, in the form of an inverted siphon; was laid to bring water across 
the cation of the west branch of Feather River; and in 1873 other pipes were laid, for a similar 
purpose, across the deep cafions of Feather River and Little Butte Creek. Since the latter date 
hydraulic mining has been carried on with great energy and success. According to measurements 
male in the summer of 1879, under the direction of the State Engineer, there have been 22,000,000 
cubic yards of gravel removed since the commencement of mining at this place. The hydraulic 
operations, up to the spring of 1880, were carried on principally by the Spring Valley Mining and 
Irrigating Company, which, by consolidations and purchases, had acquired a large extent of mining 
ground, variously estimated as comprising from 320 to 440 acres. The differences of these esti- 
mates are to be accounted for by the differences of opinion in regard to the proper classification of 
some of the ground owned by the company. Since the date of my visit this property, together 
with nearly 900 acres of ground adjoining it on the southwest, belonging to the Cherokee Flat 
Blue Gravel Company, has been purchased by a new organization, the Spring Valley Hydraulic 
Gold Company, for the reported sum of $2,000,000. As no mining of consequence has been 
done on the ground formerly owned by the Blue Gravel Company, my field observations were 
made principally at the mines of the Spring Valley Company; and, in what follows, reference will 
be made to the property of that company alone, unless the contrary is stated. 
The portion of this ground which has been worked lies near the base of the Sugar Loaf, partly 
to the north of it, in Campbell’s Ravine, and more extensively in Saw Mill Ravine, between the 
Sugar Loaf and the main body of Table Mountain. In the former, or upper mine, the direction 
of the long axis of the excavation is S. 35° W. (magnetic) ; in the lower mine, S. 30° E. (mag- 
netic). A portion of the northern and eastern boundary of the deposit, as indicated by the pres- 
