That's SLO Weird

Old mercury mines sit abandoned across SLO County — and they’re hiding in plain sight

Editor’s note: “That’s SLO Weird” explores the things that make San Luis Obispo County so wonderful and so ... well ... weird. Wondering about something weird in SLO County? Send your tips to Gabby Ferreira at or @Its_GabbyF on Twitter.

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Mercury mines were once a critical player in San Luis Obispo County’s economy.

They helped keep America’s economy running — playing a part in everything from the California Gold Rush to World War II.

One SLO County mine even helped establish Cambria as a city, back in the 19th century.

Now that mine, as well as many others, are hiding in plain sight.

What happened?

How the mines came to be

When you think of mines, you probably think of the ’49ers panning for gold in Northern California, or the silver and copper mines of Arizona and Nevada.

San Luis Obispo County likely isn’t at the top of your list.

However, mining was a driving force in the county’s development. The prospectors in these parts dug mercury — or quicksilver, as it was first called — out of the earth.

There are perhaps four major mercury mines in San Luis Obispo County: Rinconada, near Santa Margarita, Klau and Buena Vista west of Paso Robles and the Oceanic mine near Cambria. The county is home to about 150 mercury mines, according to Tribune archives.

People knew that cinnabar — the ore from which mercury is extracted — existed in San Luis Obispo County long before it was mined. Cinnabar was used as paint by the indigenous inhabitants of SLO County, according to Myron Angel’s book, “History of San Luis Obispo County.”

The story of how mercury mining came to the area varies, but most accounts pinpoint the date to 1862.

Tribune articles from the 1980s and 1990s say cinnabar was discovered either by “a party of Mexicans near the origins of Santa Rosa Creek in Cambria” or by “a Mexican prospector on the summit of the Santa Lucias, between San Simeon and Paso Robles.”

That discovery led to the Little Bonanza, a small group of mines about halfway between Cambria and Paso Robles, that “were only worked sporadically,” according to the Cambria Historical Society.

The Buena Vista and Klau mines both opened in the 1860s. The Buena Vista Mine ceased operating in 1970, and mining at the Klau Mine stopped a few decades before that.

The Rinconada Mine opened in the 1870s. It operated intermittently until about 1968, according to a report on the mine from the U.S. Environmental Protection Agency.

The Oceanic Mine opened around 1865, and production ceased in 1882, following a drop in the price of mercury. That mine was operated intermittently until it was permanently shuttered in 1958, according to the Cambria Historical Society.

After the Gold Rush, mercury was used to extract gold and other precious metals from crushed ore.

And during the Civil War, mercury was used both to process the silver used to pay Union forces and to manufacture “detonating devices” used by Confederate and Union armies, according to a 2018 Times Past article in The Tribune.

»» LISTEN: Tribune reporter Gabby Ferreira discusses mercury mines on KCBX

‘Too much encouragement can not be given’

Following their establishment around the 1860s and 1870s, the mines went through many cycles of boom and bust, though the attitude in this newspaper stayed generally optimistic.

“Too much encouragement can not be given to this industry,” The Tribune said in a flowery article describing a tour of the Rinconada mine in 1875. (The reporter also described the meal they ate at the mine: “a splendid dinner of roast chicken, roast beef, fine vegetables, good bread and butter, with a dessert of pie, tea and coffee, and apples, grapes and melons.”)

The Oceanic mine, in contrast, had “a woebegone, deserted, neglected appearance,” just 15 years after it opened, according to a 1880 Tribune article. The mine apparently closed once the market value of mercury fell.

“Some day quicksilver is going to be more valuable than at present, and then this property will again become remunerative to its owners and a source of revenue to the county,” the article said.

Mercury mining was once “one of the important industries of San Luis Obispo County,” according to a 1938 Tribune article. At the time, the Oceanic mine had been shut down for five months and allowed to flood, and the Rinconada mine “has not had much production since 1929,” though six men were still working there, according to the article.

Social calls and visits were also paid at the mines.

Tribune articles from the mid- to late 1930s mention calls paid to the Woods family, who moved to the Klau Mine in 1935, according to Tribune archives. Mentions of visits to Klau and Rinconada mines are also noted in Tribune articles from the 1920s and 1930s.

But as time wore on, it didn’t seem like such a good idea to be near the mines.

Environmental hazards

Environmental hazards from San Luis Obispo County mines were noted by officials and reporters as early as the 1970s, according to Tribune archives.

In 1971, the Buena Vista Mine was putting up to 25 times the legal limits of waste mercury into Las Tablas Creek, according to a Central Coast Sun-Bulletin article published at the time.

However, the mine’s owner, Harold Biaggini, denied for years that the mine was a source of pollution — even when Las Tablas Creek turned bright orange in 1995.

At the time, neighbors told The Tribune that they suspected the Buena Vista Mine had something to do with it.

The water “looked like Campbell’s tomato soup,” neighbor Roger Gettman said.

“It makes you want to cry,” said Donna Harcourt, a neighbor whose reservoir was fed by the creek.

Biaggini didn’t comment for that article. But in 1994, he told The Tribune that there was no mercury in the creek.

“He said the strange color people see in the creek is the result of cinnabar eroded by runoff water,” according to the 1994 article.

In 1996, lettuce and spinach sold at Charan Springs Farm in Cambria was found to be contaminated with mercury.

The contamination came from “tailings from an abandoned mercury mine about five miles east of Cambria,” and caused a health scare, though urine tests of people who had a history of eating produce from the site turned out fine, The Tribune reported at the time.

Mine tailings are byproducts left over from mining.

A Tribune article from 2006 said the farm was located on the former site of a mill for the Oceanic mine.

In 2003, federal officials temporarily closed the Rinconada Mine area to the public in advance of a planned EPA cleanup of the site, according to a Tribune article published then. A 1965 article noted that “the Rinconada has been mined until the mountain looks from the inside like a Swiss cheese.”

The Klau and Buena Vista mines are listed as Superfund sites on the EPA’s National Priorities List, which contains “the most serious uncontrolled or abandoned hazardous waste sites throughout the United States,” according to the U.S. Department of Health & Human Services.

According to the EPA, officials have stabilized the Klau and Buena Vista site, which “reduced the discharge of acid mine drainage and discharge into Las Tablas Creek.” The Klau Mine is the only mine in San Luis Obispo County that produces acid runoff, according to a 2006 Tribune article.

EPA work on the Rinconada mine appears to have halted after the 2003 cleanup, but it’s ongoing at the Klau and Buena Vista mines.

The impacts of the Klau and Buena Vista mines reverberate to this day. There are still restrictions on consuming certain types of fish from Lake Nacimiento based on mercury levels, according to an advisory from the California Office of Environmental Health Hazard Assessment.

Mercury is a toxic and dangerous substance. High exposure to mercury may result in damage to the nervous system, kidneys and gastrointestinal tract, according to the EPA.

Where are the mines now?

The mines’ heyday is long past, and the wilderness has begun reclaiming them. But you can still find them, if you know where to look.

Rinconada Mine is located just off the Rinconada Trail, out by Pozo. At least part of the land is privately owned, according to Margot Perez-Sullivan, a spokeswoman for the EPA. It is accessible from the hiking trail, but beware: It’s an abandoned mine, after all.

Klau and Buena Vista mines are off Cypress Mountain Road in the Adelaida area. They are mostly privately owned, but “a small amount” of the land is owned by the Bureau of Land Management, Perez-Sullivan said.

The Oceanic mine was located 5 miles up Santa Rosa Creek from Cambria, according to the Cambria Historical Society. At least some of the old mine property is now part of Charan Springs Farm, according to Melody Coe at the Cambria Historical Society.

“Mine sites should not be visited by members of the public,” Perez-Sullivan said in an email.

Abandoned mines are generally unsafe places to be, according to, a website managed by the Bureau of Land Management.

People could fall down mine shafts concealed by debris, the website says.

Support frameworks in mines can decay over time, so tunnels could collapse. And some abandoned mines aren’t well-ventilated, meaning pockets of deadly gases could form with no warning. Toxic chemicals could also be present, and people may become lost or disoriented when entering a dark mine tunnel, according to

“Active and abandoned mine sites have proved to be an irresistible — and sometimes deadly — draw for children and adults,” the website says.

If you do decide to visit San Luis Obispo County’s mines, proceed with caution — but these one-time titans of a long-gone industry are probably best left alone.

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Gabby Ferreira is a breaking news and general assignment reporter at The Tribune in San Luis Obispo. A native of Houston, Texas, she was a reporter in Tucson, Arizona; Indianapolis, Indiana; and Palm Springs, California, before moving to San Luis Obispo County in 2016.