206 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
“ At the present day, where the top-gravel only is washed, it is thought to do very well if it 
yields from ten to fifteen cents per inch of water for ten hours. In the North Bloomfield Com- 
pany’s mine, in 1870-71, the yield of surface gravel was sixteen cents per 24-hour inch, or six 
and six tenths per 10-hour inch. From 1870 to 1874 the yield was only thirteen and six tenths 
cents per 24-hour inch, equal to five and sixty-six hundredths cents per 10-hour inch. In 1875 
the top-gravel, including a little blue gravel, but nothing within forty feet of the bed-rock, yielded 
nineteen and two tenths cents per 24-hour inch, or eight cents per 10-hour inch. It is quite prob- 
able, however, that the water in this mine, furnished as it is from the Company’s own ditch, is 
much more lavishly used than in mines where it is purchased, and the relation of water to product 
would, on that account, be an unfair criterion for other mines. At Columbia Hill, where only top- 
gravel has been washed, its yield in several instances, of which more details are given farther on, 
has varied from about twenty cents to fifty-eight cents per 24-hour inch, affording in the instance 
last referred to exceptionally good profits. 
“Some of the mines below San Juan afford the most satisfactory examples of the results of 
washing the entire bank, including together the top and bottom gravel. The record of their obser- 
vations during the past four years, where they can be obtained, furnish the best data for judging 
the value of the ground. Of this portion of the channel some two or three miles have been 
already washed out. The American Mine has been worked for a length of about 3,000 feet along 
the channel. The width of the cut from rim to rim is probably 1,000 feet, and the workings 
about 140 or 150 feet. From some data furnished from the Company’s books a few years since, 
it appears that the gross product of the mine from December 19, 1860, to August 6, 1872, was 
$ 1,241,240.30. The water used in this period was 1,454,174 inches of ten hours, and the yield 
per 10-hour inch would accordingly be eighty-six cents. The price paid for the water varied from 
sixteen and two thirds to twelve and a half cents per 10-hour inch, amounting in the aggregate to 
$ 218,749.58, or 30.6 per cent of the whole working expense. The last-named item was 
$ 714,771.04, and the net proceeds $526,469.27, or 42.41 per cent of the product.* 
“These examples might be supplemented by others, but enough has been said to warrant the 
conclusion that the top-gravel alone usually contains gold enough to pay the expenses of mining, 
and leave a profit for the owner of the water ; and, further, that where the blue or bottom gravel 
has been washed, it has, with very rare exceptions, made satisfactory profits for the owner ; finally, 
in order to reach the blue gravel, the top-gravel must be removed.” 
In regard to the quantity of gravel yet remaining on the divide between 
the South and Middle Yuba rivers, and not too deeply covered to be washed, 
it is impossible, at present, to make any statement which could have any 
claim to accuracy. It is safe to say, however, that with the present available 
supply of water this gravel will not be exhausted during the present century. 
Mr. Hague estimates the linear extent of the main channel and its branches, 
on this ridge, at not less than twenty-five miles, and considers that, deducting 
liberally for the portion already worked, and for that too deeply covered by lava 
to be available for hydraulic mining, there are probably not less than four- 
teen miles of channel still available for washing.t Roughly estimating the 
average width of the remaining gravel range at 400 yards, and the average 
* In 1871, Mr. Hamilton Smith estimated that the yield of this ground amounted to twenty-four cents 
per cubic yard, and that each linear foot of channel worked had paid at least $750. 
+ This estimate was made two years ago. 
