Natural Hydraulic Mining

For a number of decades after California's Gold Rush started in 1849, some firms used hydraulic mining (huge high pressure hoses aimed at the sides of hills) to knock gold deposits into rivers to be recovered by sluice boxes.   This had substantial consequences downstream, including changing shoreline of San Francisco Bay.  2/27/17 CBS San Francisco reports on the natural form of hydraulic mining:

JAMESTOWN, Tuolumne County (KPIX 5) — Weeks of rainy weather across Northern California and the storm runoff through the hills of gold country have triggered a new gold rush.

“Miner Gary” Thomas said he always finds at least a little gold here on his property near Jamestown in Tuolumne County, but this year, there’s so much more runoff than normal and it’s shaking the gold from these hills.

Thomas said it could provide a “Eureka” moment for those inclined to come up here and look for it. “(The runoff) kind of ‘etch-a-sketches’ everything,” said Thomas. “Eveything I had dug up and now my dig spots are all gone.”

The known gold digs were washed out, trees uprooted, and landscape eroded. The runoffs have also removed gold out of the old abandoned mines and sent it down the river.