When Jason Chellew died, after he and the middle of his home plunged into an apparent old mine shaft recently in nearby Alta, Nevada County residents may have wondered if they were in similar danger.
While the underground Grass Valley and Nevada City area is honeycombed with old hardrock gold mine excavations, they are generally deep and steeply pitched at the surface. What apparently brings real danger is what is truly close to home.
“When you get closer to the surface and the soil is when the problems occur,” said Tom Holdrege of Holdrege & Kull Consulting Engineers & Geologists of Nevada City. “Two to three times a year we get calls of suspicious sinkholes, like somebody’s driveway caves in.”
Holdrege could only remember one home that was threatened by a sinkhole. That was the home of Just Willis on Bet Road outside of Grass Valley off Brunswick Road in 1998. Like the Chellew sinkhole, and the recent landslide on Allison Ranch Road, heavy spring rains probably primed the disasters.
The Union could not locate Willis, but an archived story said he had to abandon the home after a 30-foot wide hole, about 15 to 20 feet deep, opened up right outside his front door and exposed the foundation. At that time, an old miner told The Union the home was built over the original shaft of the Old Brunswick Mine.
“He had unusual circumstances too,” Holdrege said. “His septic tank was leaking or leaching right outside his house,” and made the ground even more unstable.
It is that kind of situation that causes the Nevada County Building Department to ask for geotechnical reports when people build or put a septic tank in a suspected mining area.
“We don’t want to put a $500,000 home over a hole,” said Brian Washko, director of building. “A lot of places have mine shafts, but no one knows where they all are.”
Washko said information of old mining activity is supposed to be listed on property documents and divulged prior to transactions. But that does not mean that all old mine shafts, drifts and tunnels information always exists.
“The only guys who know that are gone,” said Tim Abraham, a longtime employee at the assessor’s office which has no thorough maps of old mining excavations. But he can show you abandoned mine holes like the one he found in the 1960s – just south of Grass Valley – during a family outing.
“It was vertical and I couldn’t see the bottom,” Washko said.
To find better information, “you’d have to find the original (mine) patents,” at the recorder’s office, upstairs from his office in the county Rood Center.
Indeed, bound volumes of mine patents, claims and general records are there, according to Sonja Hann, a recorder’s assistant. Once there, people can look up old mines by section, township and range, “which can be cross-referenced,” she said, to see if one or more are under their property.
What to look for
There are no full-scale maps of mining activity at the Empire Mine State Historic Park, according to Glen Boire who works the front desk. However, there is a model of five square miles of tunnel, shafts and drifts under the Grass Valley area. But again, most of those are very deep, down to almost a mile underground.
“The problem is that some guys would dig a hole 30 feet deep and give up on it without filling it back in,” Boire said of Gold Rush-era miners. “They called them coyote holes.”
“We call them prospector pits,” Holdrege said of the depressions or shafts that his firm closes or fills in for clients every year.
Other signs of mining activity include large piles of mine waste rock on the ground, Holdrege said. They are often referred to as tailing piles, but that infers they have been chemically treated and that is not always the case.
Washko said people can also look for concrete abutments or old building foundations that might have been used by miners.
“If you’re walking on a piece of property and you see tailings or holes in the ground, something’s going on,” Washko said.
Reporting old mines
When people do find abandoned mines, shafts or tunnels, the state of California wants to know about it.
According to Doug Craig, assistant director of the Office of Mine Reclamation in Sacramento, there are 47,000 abandoned mines in California. So far, the Abandoned Mines Unit of the office has located 2,300 of them, partially with the help of the public.
If you suspect you have found one, his office wants you to call 1-877-OLD MINE, or 1-877-653-6463, and tell them.
If it is an old mine and presents a danger to the public, it can be capped off.
If bats are living in it, a cage or special gate can be placed over the top so the species isn’t removed from the scene.
Craig said property owners can also find old information about mining at the California Geological Survey Library in Sacramento.
The recent separation of Allison Ranch Road just outside Grass Valley, due to a rain-induced landslide, could be over an old mine site. Although piles of mining waste rock sit around the site, county engineer Doug Farrell said the ground needs to harden more before an investigation is held to determine if an old mine is there.
To contact senior staff writer Dave Moller, e-mail email@example.com or call 477-4237.
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