South of Plumas is Sierra county, which is fifty miles long from east to west, and twenty miles wide from north to south. The North Fork of the Yuba River runs through its centre, and the Middle Fork is its southern boundary. Though small, it is one of the richest mining counties of the state, and in proportion to the extent of its mining ground, is much richer than any other county. All its territory is four thousand feet above the sea level, at the lowest. Most of the mining is done in hydraulic and tunnel claims in deep hills. Near the centre of the county is a mountain called the Downieville Butte, or the Yuba Butte, eight thousand eight hundred and forty-six feet high, on the sides of which are found some rich quartz leads. In 1859 there were eleven quartz-mills in Sierra county, of which seven are at the Butte, two at Downieville, one at the Mountain House, and one at Sierra City. The principal mining towns are Downieville, Monte Cristo, Pine Grove, St. Louis, La Porte, Poker Flat, Eureka City, Forest City, Alleghany Town, and Cox's Bar. One of the most remarkable features of the placers of the state, is the blue lead, which was first discovered in Sierra county, and has been more thoroughly examined there than elsewhere. The "blue lead" is a stratum of blue clay very rich in gold. It is found deep under other strata. The general opinion is, that the blue lead occupies the bed of a large antediluvian river, which ran parallel with the Sacramento and about sixty miles eastward of it. It has been traced twenty miles or more, passing near Monte Cristo, Alleghany Town, Forest City, Chip's Flat and Zion Hill. Mr. C. S. Capp wrote thus to the San Francisco Bulletin:
"This is not one of the many petty leads, an inch or two in breadth and thickness, which, after being traced a few hundred feet, end as suddenly and mysteriously as they commence; but it is evidently the bed of some ancient river. It is often hundreds of feet in width, and extends for miles and miles, a thousand feet below the summits of high mountains, and entirely through them. Now it crops out where the deep channels of some of the rivers and ravines of the present day have cut it asunder; and then, hidden beneath the rocks and strata above it, it only emerges again miles and miles away. Wherever its continuity has been destroyed, the river or gulch which has washed a portion of it away, was found to be immensely rich for some distance below, and the materials of which the lead is composed are found with the gold in the bed of the stream. It is evidently the bed of some ancient stream, because it is walled in by steep banks of hard bed-rock, precisely like the banks of rivers and ravines in which water now runs, and because it is composed of clay which is evidently a sedimentary deposit, and of pebbles of black and white quartz, which could only be rounded and polished as they are by the long continued action of swiftly running water. The bed-rock in the bottom of this lead is worn into long smooth channels, and also has its roughness and crevices like other river beds. The lighter and poorer qualities of gold are found nearest to its edges, while the heavier and finer portions have found their way to the deeper places near the centre. Trees and pieces of wood, more or less petrified and changed in their nature, which once floated in its waters, are also every where encountered throughout this stratum.
"The clay and fine gravel in which these pebbles and boulders are found to be tightly packed, is of a light-blue color, which gives the name to the lead. Much of this clay is remarkably fine and free from coarse particles, and is smooth and unctuous to the touch. It is said to be strongly impregnated with arsenic, as was shown by chemical analysis, and contains large quantities of iron and sulphur in solution, for pyrites and sulphurets of iron are deposited in shining metallic crystals in every vacant crevice. Fine gold is found among this clay, and the heavier particles beneath it, upon the bed-rock. This stratum varies in thickness from eighteen inches to eight or ten feet, while the whole lead varies in width from a hundred and fifty to five hundred feet.
"The same lead has been found at Sebastopol, four miles above Monte Christo, and also higher up among the mountains. It appears at Monte Christo, which is four miles above the high-lying Downieville, and over three thousand feet above it, and at Chapparal Hill on the side of a deep ravine; then at the City of Six, which is also on very high land, about four miles from Downieville, across the North Yuba. It is next found at Forest City, on both sides of a creek, and is there traced directly through the mountain to Alleghany Town and Smith's Flat, on the opposite side. There it is again cut in twain by a deep ravine. It crops out on the other side at Chip's Flat, where it has been followed by tunnels passing completely through the mountain to Centreville and Minnesota on the other side. Here it is obliterated by the Middle Fork of the Yuba, but it is believed to be again found at Snow Point, on the opposite side of the river, and again at Zion Hill, several miles beyond. There is no reason for doubting that after thus reaching over twenty miles, it still extends further. Hundreds of tunnels have been run in search of it. Where the line it follows was adhered to, they have always found it, and have been well rewarded for their labor. Millions of dollars have been taken from this lead, and its richness, even in portions longest worked, is yet undiminished. These tunnels have cost from $20,000 to $100,000 each, and interest in the claims they enter sell readily at from $1,000 to $20,000, in proportion to the amount of ground within them remaining untouched, and the facilities which exist for working it. Many of these claims will yet afford from five to ten or more years' profitable labor to their owners, before the lead itself within them is exhausted. As in some of them quartz veins and poorer paying gravel have been found, many of them may be valuable to work from the top down as hydraulic claims."
This idea that the blue lead occupies the bed of an antediluvian river is however not universally accepted. Mr. B. P. Avery, who has written numerous newspaper articles upon the mineral deposits, asserts that the "blue lead," as it is called, is not a "lead" but an extensive stratum which is many miles wide, and is found all the way from the foot hills to the summit of the Sierra Nevada. In reply to this, it is said that while a bluish stratum of clay similar to that of the blue lead is found over a wide district, that it is evidently different in origin from the blue lead itself, which is confined to a narrow bed, and marked by the signs found in all the other ancient river beds of the state.
The Sierra Butte Quartz Mining Company has some of the best auriferous quartz lodes in the state. One lode called the Cliff Ledge, is twenty-five feet wide; and another called the Aërial Ledge, is about three feet wide. In the Cliff Ledge, the paying rock averages about six feet in thickness next the foot wall. The average yield is eighteen dollars per ton. The quartz is bluish white in color, and very hard when first taken from the lode, but on exposure to the air it slowly crumbles into sand.
Yuba and Butte.—West of Sierra county, and drained by the same streams, is Yuba, which reaches to the Sacramento River, lying half in the mountains and half in the plains, the mining district being in the former half. The principal mining towns are Camptonville, Timbuctoo, Foster's Bar, Texas Bar and Long's Bar. In 1859 there were nine quartz-mills in the county, three at Brown's valley, and one each at Camptonville, Dobbin's Ranch, Dry Creek, Honcut, Indiana Creek and Robbin's Creek. The assessor in 1860 reported only two quartz-mills in the county. There are twenty-two ditches in the county, with an aggregate length of nine hundred and fifty-two miles, an average of forty-three miles each. The most important ditch, called "Bovyer's," supplies Timbuctoo with five thousand inches of water in the winter, less in the summer. The diggings at Timbuctoo are in a deep hill, which is washed away by the hydraulic process.
West of Yuba and Plumas counties lies Butte, which is drained by the Feather River. The principal mining towns are Oroville, Bidwell's Bar, Forbestown, Natchez and Whiterock. In 1859 there were seventeen quartz-mills in the county, of which four were at Oregon Gulch, at Columbiaville and Hansonville, three each, two at Yankee Hill, and at Evansville, Gold Run, Long Bar, Nesbitt's Flat and Spring Valley, one each. The assessor reports for 1860, twenty-nine quartz-mills, worth fifty thousand dollars, and crushing in the aggregate one hundred and sixty-two and a half tons per day. There are sixty-four mining-ditches, with an aggregate length of five hundred and eighty-three miles. The bars and beds of Feather River were once very rich, and some of the most extensive enterprises of river mining in the state have been undertaken within the limits of Butte county. The greatest flume ever built in California was that of the Cape Claim Company, near Oroville, in 1857. It was three quarters of a mile long and twenty feet wide, and furnished employment for two hundred and fifty men from May till November. The expenditures during that period were $176,985, and the receipts $251,426, showing a clear profit of $74,441. The next year, after the water had fallen, the company commenced its labors again; spent $160,000 and received $115,000, and thus lost $45,000. North of Oroville is a "table-mountain" with a top of basalt, covering a rich deposit of auriferous clay.