What I saw. (Re-posted, 'cause it got messed up.)

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According to the geologist:

That is the largest gold-mining operation in the lower 49. It covers about 75 square miles. It is huge. The ridges you can see from space; they're contoured hills, about one hundred and thirty feet high, that didn't exist a hundred years ago. Those hills are cast up tailings from digging up gravels for gold. That whole claim has been mined several times at successive depths. The last pass mined gold from two hundred feet down.

You mine gold from two hundred feet down with a bucket line dredge. The bucket line dredge is essentially a floating factory, one that digs its own pond as it goes and fills the pond behind it. It scoops gravels up in buckets, processes them through successive sieves, and dumps the tailings behind and to the side. The earliest bucket line dredges only reached down fifty feet. The next passes reached a hundred feet, than one-twenty, and the last dredge used on those fields brought up gold-bearing gravel from two hundred feet. The geologist said the buckets had to be submerged to work, but I didn't think to ask whether that was for heat dissipation or whether the water helps lift the gravel.

Anyway, the dredges are BIG.






I recommend the More Pictures link.























Buckets on dredge in Idaho.

I asked the geologist how they knew where to direct the dredge. He said they've surveyed the fields pretty thoroughly. There are mile-long series of two-hundred feet drill cores, on the two hundred feet. Then they move a mile further from the river and do it again.

But they won't be gold-mining those claims on the Yuba soon. Four or five years ago, after several years of union-owner disputes, the dredge mysteriously sank in the middle of the night. Thirty million dollars of capital, sunk. The geologist said they tried to bring it up three times with giant cranes, but couldn't. He said that there are a few sunken dredges in the tailings. The next round of mining on this claim will not be for gold. After all these years of dumping gravel and cobble in lines of hills, the next most valuable thing in those mines is aggregate for concrete.

Except maybe. There may be something we need even more from those poor chewed-up, worked over lands.