390 SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 
by Mr. Bowie in the paper to which reference has already been made.* TI could find no data in 
reference to the cubic yards of gravel which have been removed from the different mines. 
An approximate estimate of the yield of the gravel per cubic yard is from twenty-five to thirty 
cents. In Raymond’s report for the year 1873, page 19, it is stated that the average yield of the 
American Hill gravel up to the close of the year 1871, at which time there had been six million 
cubie yards washed by the hydraulic process, had been thirty cents. From Mr. Miller I learned 
that in the years 1858 and 1859 the sum of $157,000 was taken from seven “claims” at the lower 
end of San Juan Hill, each claim being of rectangular shape, 180 feet by 80, and with an average 
depth of 120 feet. This would be a yield of thirty-five cents per cubic yard. The yield of the 
lower stratum of cemented blue gravel, wherever it has been worked by itself, has been many 
times the above amount. Some statisties are given in Raymond’s report for 1873, on the page 
referred to above. 
The principal bodies of gravel left untouched are those between French Corral and Birchville, 
and between Manzanita and American Hills, the former being about a mile and an eighth in length, 
the latter nearly a mile. The average thickness of the gravel over the deep channel between French 
Corral and Birchville is probably between 125 and 150 feet, and between Manzanita and American 
Hills as much as 200 feet, or something more. 
The sulphurets found in the gravels are a source of gold which has been hitherto neglected. 
They are found in considerable quantity both on the bed-rock and in the gravel itself, and are 
caught in part by the riffles in the sluices. At Manzanita Hill the experiment of collecting the 
sulphurets at the “clean ups,” stamping, roasting, and amalgamating them, has been attended 
with a good measure of success. At French Corral the sulphurets are more abundant than they 
are higher up on the ridge. 
In the neighborhood of French Corral there are quartz veins in the bed-rock, cutting across the 
old channel, but none that have been worked to my knowledge. One outcrop, known as the Red 
Ledge, seemed to be attracting considerable interest, and I took the time to visit it. It lies upon 
the South Yuba side of the ridge, about a half-hour’s walk from French Corral, and 150 feet lower 
than the bed-rock in the gravel mines. The outcrop has the appearance of a gossan. The ledge 
has not been worked enough to show precisely what it is. I took a few specimens of the ore for 
future examination. One peculiarity of this ledge is that the gold obtained from it is only from 
-640 to .650 fine, the remainder being silver.t 
B. Lone Ripce anp Montezuma HItt. 
The Lone Ridge deposit of gravel lies about a mile and a half to the southeast of the town of San 
Juan, and a half-mile westerly from the Oak Tree Ranch, the position of which has been marked 
for correction on the Gravel Map. The gravel lies in the eastern half of Section 9, as the section 
lines are drawn upon the General Gravel Map. It is an interesting deposit, principally on account 
of its altitude, the bed-rock being fully 500 feet above that at the eastern end of San Juan Hill, 
or nearly as high as the site of the hotel at Cherokee. The gravel lies on the summits of two or 
three hills or short ridges at the head of a ravine leading down to the Oak Tree Ranch. Several 
shafts have been sunk upon the ridge, and have proved the existence of a bed of gravel with a 
thickness of at least seventy feet. The vravel is fine, loose, and shingly, with no cement, and 
carries fine gold all the way down to the bed-rock, which is granite. The crest of the main ridge, 
which is not very wide, is nearly level for a quarter of a mile below the tunnel mentioned further 
on, and follows a general southwesterly direction (S. 20—33° W., magnetic). From the lower 
extremity of the ridge a good view is obtained of Montezuma Hill, and down the valley of Shady 
Creek, but San Juan and its vicinity are shut off by the high ridge of country rock which lies to 
* See ante, p. 196. 
+ For information relating to this region I am indebted to Mr. N. C. Miller of French Corral, to Captain Thomas 
of the Manzanita Hill mines, to Superintendent McBride, Captain Bank, and Mr. John McCoy of American Hill, as 
well as to several other gentlemen whose names I have not preserved in my notes. 
