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October 15, 1862: Pentz

October 15, 2012

Oroville 03

Table Mountain, Oroville; by Tom Hilton, on Flickr

Camp 108

Here we spent two days, days most important in results.

There is a peculiar feature about the landscape that I must attempt to describe, although I fear that I cannot well make you understand it. Several of these volcanic ridges terminate here, and before they sink to the plain curious table-lands are left. The whole surface of the country has been washed away in places, except where protected by patches of lava. A hill is thus formed, a perfect “table”….

These hills are sometimes long ridges, at others, near camp, mere round hills, the lava washed away on all sides, leaving those isolated tables. The tops are bare rock, or nearly so. They are nearly level, with a slight descent toward the valley, the same slope down which the lava once flowed. You cannot imagine what a peculiar feature these hills, or “table mountains,” impart to the scenery of the landscape.

And while I am at it, I may as well enlarge on this and tell you more about that great feature, the table mountains of this state. The kind I have just been describing are caused by great sheets of lava having flowed over great districts, thousands of square miles together, and then being partially worn away in later times by the denuding actions of our terrible winter rains.

There is another kind, however, still more remarkable, more noted, and of immense pecuniary importance. The Sierra Nevada, as I told you, is a broad chain, from 60 to 150 miles wide, and from 6,000 to 13,000 feet high. Its width is the great feature. It appears to have been upheaved, and then furrowed by water into great canyons, valleys, and “gulches.” The gold is disseminated thinly through the slate rock. This slate (or quartz veins in it, with gold) has been worn down, powdered by rains and streams, the lighter materials washed into the great valleys below, the gold left in the gulches because of its greater weight; and here it is found, concentrated as it were, the gulch being a natural sluice that has been worked by nature for ages—man has only to “clean up” the gold. These are the “placer mines” of the state.

Now, the lava flowed over this country after much of this denudation had taken place. Immense districts, which would otherwise be gold bearing, are barren because covered up by these lava deposits.

All through the Sierra there have been immense craters, or “vents,” from which enormous quantities of lava have flowed, the steams streaking the slopes, and forming table mountains….1

Now these are old lava streams, long and narrow. There is a table mountain in Tuolumne County that is ninety miles long, and never over a mile wide, generally less than half a mile! How could it have been formed? you ask, and the answer is the extraordinary part of the story. This lava, now the top of a mountain, ran in a stream in the bottom of a valley! Those hills of softer slate have been worn down until they are the valleys, while the harder lava has withstood the elements and forms now the top of the mountain. Most extraordinary fact!

….Now, upon this fact is founded an important element in one kind of mining—“tunneling”—which proves that these streams of lava flowed down the valleys of old rivers. The mountain is tunneled, often at an enormous expense, to find the old river bed, and from that get the gold….

Between the table and the rim rock is a bed of gravel, once the soil of the surface before the molten streams of lava flowed on. This gravel is thickest in the old river bed, where they find the gold mixed with sand, gravel, and cobblestones, the whole generally cemented together into a hard, firm mass, like rock.

To get it, they pierce the rim rock by a tunnel…and herein is the great labor and risk. If the tunnel is begun too high, they strike above the old river bed, and hence must work at an immense disadvantage. If too low, they may pass through the mountain and not find the bed at all. This bed sometimes is beneath the middle of the lava table, at others near one side, so that should the tunnel be begun on the wrong side it must be carried to great length.

Under these mountains, you find all the evidences of the former river—not only sand, pebbles, and gold, but sometimes pools which have been filled with clay, most beautifully stratified, and containing leaves, bits of wood, etc. Some of these leaves are as plain and beautifully distinct as if their impressions were taken but yesterday in wax or putty. The bones of animals—mastodons, elephants, etc.—are also found; these, however, are rare. California, like eastern America, was once the home of these huge animals, and their remains are often found in the placer and hydraulic diggings. We have the perfect skull of a horse (extinct species) with teeth all in, found thirty-five feet underground—the teeth of elephants, mastodons, tapirs, camels, etc., and a few days ago the underjaw of a rhinoceros nearly perfect!

1Brewer’s letter included diagrams illustrating his description; these may be seen here.

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