San Benito County History

This section is excerpted from A Memorial and Biographical History of the Coast Counties of Central California by Henry D. Barrows and Luther A. Ingersoll, and published by The Lewis Publishing Company in 1893.

Return to Index

Quicksilver - New Idria.

As is well known, the New Idria quicksilver mines rank among the most famous in the world. They are situated in the western end of Vallecitos valley, on the southeastern borders of San Benito county, in the portion acquired from Fresno. These mines were discovered about the year 1852 or 1853. Work was first commenced upon a deposit of chromic iron at the top of the mountain near the boundary line between Monterey and this part of San Benito county, then a portion of Fresno, under the impression that it was silver ore.

Through assays made by the old padres of Monterey cinnabar was discovered where New Idria now stands, and about 1854 or 1855 the New Idria mine was located.

The lode is a large body of ore, in some places having been worked to a width of two hundred feet. The vein has a general pitch toward the south of from forty-five to sixty degrees.

The foot-wall is a "silico-argillaceous" slate. In the lower workings there is a dark-colored clay, from a few inches to a foot or more in thickness between it and the vein matter. The hanging-wall is a similar slate, but rather more compact in structure, often presenting a slicken-side surface toward the vein, and being easily broken into glossy laminae.

The vein matter varies in different parts of the workings. The better grade of ore has been found in the highest and western portion of the mountain. Most of the gangue is hard and siliceous, but at some times it is slaty or of a clayey nature, often containing much oxide of iron. The ore richest in mineral is usually found toward the hanging-wall. Below the Day tunnel, as far as has yet been explored, the vein becomes poorer, and the gangue, which is at first siliceous or slaty, changes to a sandy character. The New Idria mines are all in the northeastern slope of the mountain, which rises to the height of about 1,500 feet above the reduction works, which are situated at its base; the summit of the mountain is between 4,000 and 5,000 feet above sea level. There are over one and one-half miles of tunneling in the New Idria mines, not including the huge chambers which have been dug out in the heart of the mountain. The highest workings are the oldest, and are at the ridge of the mountain. These consist of an incline running down upon the vein to the Sleeman tunnel. This tunnel, which is about 900 feet above the reduction works, runs south into the mountain for a distance of 700 feet, and was made in 1859. About 200 feet lower down is the Myers' tunnel, which was commenced in 1859 and finished in 1860. This penetrates the mountain to a distance of about 1,000 feet. It is from this tunnel and the Sleeman that the highest grade of ore and the largest quantities have been taken. The ore here also appears to be the most ferruginous, and at one point, where a small stream of water drips from the roof, there are to be seen stalactites of sulphate of iron. Upon the walls of all the upper workings, fibrous gypsum forms in beautiful tufts like glossy moss. Some 200 feet lower down, and about 600 feet above the reduction works, is the Day tunnel. This also was started in 1859, and penetrated the mountain to a depth of 1,500 feet. This tunnel has been prolonged outwardly by timber, in order to allow dumping facilities for the work above, that otherwise would have covered up the mouth of the Day tunnel. The dump of the Myers' tunnel above has accumulated and slidden down upon the prolongation until there are over 100 feet at the commencement of the Day tunnel running under this waste rock.

All these workings, from the top of the mountain to the Day tunnel, constitute the upper portion of the mine, and are connected with each other by various tunnels and up-raises. About one hundred feet above the reduction works, and 500 feet below the Day tunnel, is the Bell tunnel, or lower workings, about 4,000 feet in length. This tunnel is timbered almost throughout its entire length with closely set timbers, there being over 3,000 sets, with lagging both on the roof and sides. Each set requires a log twenty feet long and ten inches in diameter. The temperature in this tunnel is high, and the atmosphere damp and oppressive. Whether it is the effect of the heat and moisture, or some gaseous exhalation of the formation is not known; but the timbers decay in an unusually short time, and two men are kept constantly employed in replacing the old ones by new. This rapid decay is more marked during sultry weather, when the draft in the tunnel is almost nil and the atmosphere oppressive. Timbers immersed in water, or those which are kept constantly wet by seepage, do not seem to be so affected. Dry, seasoned wood lasts the longest. Timbers, after having stood in place for only thirty-six hours, have accumulated a mildew one inch in thickness.

The furnaces of the New Idria mines are of the same style as those in use at the Idria, Austria, being square, about thirty feet in height, ten feet in width, and twelve feet in length. The furnace is fed at the top by means of a drop hopper, at the rate of one ton per hour, and holding twenty-four tons when full. There are employed two men to each shift of twelve hours on the furnace, and fifty men in and about the mines. The fuel used is almost entirely manzanita and oak, which is delivered at the furnace at $6.50 per cord, one cord being consumed every twenty-four hours.

A condensed history of the Mexican grant, "La Panoche Grande," on which these "New Idria quicksilver mines" were discovered, may be found in another part of this work.

The enormous output of these mines, which are claimed only by a squatter's title (by a company composed largely of foreigners or of persons living in foreign countries) has enabled the claimants of the mines to contest the title to the ranche for thirty-five

years, notwithstanding the fact that said title has been pronounced genuine, and that a patent was ordered issued therefore nearly thirty years ago. The case is one of the most anomalous in the history of this country.

Return to Index

This section is excerpted from A Memorial and Biographical History of the Coast Counties of Central California by Henry D. Barrows and Luther A. Ingersoll, and published by The Lewis Publishing Company in 1893.