On Jan. 24, 1848, James W. Marshall discovered gold in Coloma, Calif. “Boys, by god, I believe I’ve found a gold mine,” he’s said to have exclaimed.
What happened next is a story that’s been told countless times.
People from around the world descended on the Sierra Nevada range of California seeking their fortune. Solitary prospectors crouched by streams, shaking around gravel in a pan to extract a few nuggets of gold. Within less than a decade, they went home, and the Gold Rush was over.
It’s a romantic story in a way. It’s also a myth.
One doesn’t have to visit bucolic Gold Rush towns like Coloma, where you can give panning for gold a try, to see the truth. Before 1975, there was no state or federal law mandating cleanup of mining operations. Today, California’s Department of Conservation estimates that there are at least 47,000 abandoned mines dotted across almost every county in the state. Every year, a few people still fall into old mine shafts or get lost in their maze-like tunnels. And about 5,000 of these mines, according to state estimates, are also likely contaminated — leaching out harmful heavy metals like arsenic, lead, and mercury that were dug up from deep underground or added to the environment in a desperate attempt to extract every nugget of gold.
“There’s little spots of contamination all over,” says Joanne Hild, a longtime resident of Nevada City, one of the state’s most important gold-mining towns. “People don’t even realize that the lump in their backyard could be mining-contaminated.”
When the prospectors known as the 49ers descended on California, the gold deposits they could excavate by hand, a form of what’s called placer mining, were actually played out in a year. But intensive mining continued for decades. Once the visible flecks were gone, miners developed more invasive means of getting at the gold. They dammed and diverted waterways to strain whole stream beds. Massive barges trolled lakes in the mountains, suctioning up bottom dirt. In some places, they used a technique called drift mining, where they would dig sideways into slopes of jumbled gravel, tracing the channel of ancient gold-bearing rivers.
In their maniacal search, California gold seekers also invented hydraulic mining, akin in some ways to the notorious practice of mountain-top removal in coal country.
In California, miners used powerful water cannons to wash away the hillsides above gold-bearing streams. Each cannon, with nozzles up to 8 inches wide, could shoot water out at over 100 miles per hour, ejecting 185,000 cubic feet of water — enough to fill well over 100 backyard swimming pools — every hour. What took nature millennia to build could be brought down in a matter of minutes. They then flushed the resulting slurry of mud, gravel, and rock down a long trough, or sluice box, and the gold would settle along corrugated riffles at the bottom.
By the mid-1880s, miners had washed away 100 million cubic yards of debris, enough to cover all of New York’s Central Park with 20 feet of mud, dirt, and gravel.
The Gold Rush is “presented as a sort of windfall adventure, where everybody goes and everybody gets rich and kooky things happen,” says Andrew Isenberg, a history professor at Kansas University. “It’s also presented as environmentally benign.”
In reality, the downstream impacts of hydraulic mining were devastating. At the state’s largest hydraulic mine, Malakoff Diggins, a mining company left behind a pit — almost 7,000 feet long and over 3,000 feet wide in some places — with steep, crumbling slopes that look like the Badlands of South Dakota. The debris flowing unfettered from the mine clogged rivers downstream. Commercial navigation for ships that once plied the Sacramento River from the Golden Gate to the foothills of the Sierra was soon impossible.
Residents and farmers built higher and higher levees to confine the polluted rivers flowing down from the mines, but they regularly broke through. With each flood, farmland would be coated in a layer of mud and fine silt, called slickens, full of toxic metals from the mines.
In an 1873 California guidebook, author Charles Nordhoff observed the moonscapes produced by hydraulic mining. He recounted stories from older residents who described how hydraulic mining transformed the Yuba from a “swift and clear mountain torrent” into a “turbid stream.”
“It once contained trout,” Nordhoff wrote of the Yuba. “Now I imagine a catfish would die in it.”
Despite the devastation wrought by hydraulic mining, there was little political will to adequately address it. Then, in 1884, a judge ruled in favor of a farmer whose land had been repeatedly flooded, declaring hydraulic mining a “public nuisance” and effectively ending the practice in California.
That didn’t mean, though, that the gold-mining industry collapsed. In fact, “lode” mining, the method used when gold is trapped in quartz veins deep underground, continued in California well into the 20th century.
Empire Mine, for example, is often considered one of the largest and most lucrative mines in the country. Though the deposit at Empire was discovered at the height of the Gold Rush, the mine didn’t even begin to prosper until the 1870s, and it was continuously operated until 1959. By the 1940s, the main shaft of Empire angled down almost 11,000 feet and branched off into over 350 miles of tunnels. Miners would travel down into the deep labyrinth to chip and drill away at the rock. It was then brought up to the surface in carts, where it was pounded by industrial crushing machines called stamp mills.
These days one can visit Empire Mine and go on a family-friendly tour where they’ll show you the blacksmith shop and let you peek down the old shaft. Isenberg says it gives one the impression of the operation as a “rudimentary undertaking.” What the tour doesn’t describe, though, is the deafening sound of the stamp mills or the blinding electric lights that allowed the mine to operate day and night. It also doesn’t mention (at least during my visit) the millions of dollars California has spent cleaning up lingering contamination since the state purchased the site in 1975.
Water flowing through old tunnels or waste dumps can produce acid mine drainage that’s highly toxic and corrosive. The same geological processes that produced veins of gold also left behind metals like arsenic, lead, and cadmium, which were brought to the surface during mining. Those metals can contaminate water, be absorbed by plants, or be breathed in as dust, with health impacts ranging from pain and vomiting to long-term problems like asthma and cancer.
Given the threat, the regional screening level set by the Environmental Protection Agency as an acceptable threshold for lead is 400 milligrams of lead per kilogram of dirt. It’s just 35 milligrams per kilogram for arsenic. But tests performed on the Red Dirt Pile, an aptly named dump for mining waste at Empire, found concentrations of lead as high as 6,000 milligrams per kilogram. The level of arsenic was more than 2,000 milligrams per kilogram.
And then there’s the mercury. Gold binds with mercury, creating a heavy blend that’s easier to capture. Miners added hundreds of pounds of it a day into the slurry of rock, mud, and gold coming off the hydraulic mines and coated the plates where they’d crush the rocks from deep underground with it. Millions of pounds of mercury escaped into the environment, where it remains today. Lakes, reservoirs, and rivers across California have advisories to discourage people from eating local fish because of mercury contamination.
Despite the obvious risk, significant challenges remain for the cleanup. Collaboration is difficult, money is tight, and it’s not always clear who is responsible when sites cross political boundaries or the original mining companies are long gone. There are also inadequate rules for disclosing the threat of abandoned mines during real estate sales. Often these sites end up in the hands of unsuspecting property owners and under-resourced municipal governments.
And the problem isn’t unique to California. The Government Accountability Office estimates that there are over 140,000 abandoned shafts, tunnels, dilapidated buildings, and other mine features, just on federal land across the West.
As a society, we’ve come to understand the importance of the Gold Rush for reshaping the politics and demographics of the West. To a much lesser extent, we’ve come to recognize its violent impact on Chinese and indigenous communities. But we’ve yet to appreciate the sheer industrial scale of historic mining and the ways in which it permanently altered the landscape. It’s one of many aspects of American history that are poorly understood, making it harder to come to terms with the dangerous legacies left behind.
Leah Campbell is a science writer who covers the environment, infrastructure, and disasters.