Toxic trails

A new report discovers not gold, but hazardous contaminants in popular recreation areas

Walking the Olmstead Loop trail in Cool: probably safe. Other toxic Gold Country recreation areas: not so much.

Walking the Olmstead Loop trail in Cool: probably safe. Other toxic Gold Country recreation areas: not so much.


Gold-rush-era ghosts lurk in the Sierra Nevada foothills—ghosts in the form of arsenic, asbestos, mercury, chromium, lead and other toxic minerals.

The minerals are the leftover legacy of intensive mining during the 1800s—activity that now poses health risks on recreational trails that run through abandoned mine sites.

“This is one of the most overlooked environmental problems in the state,” said Carrie Monohan, science director for The Sierra Fund and lead author of a June report on the toxic legacy of gold-rush-era mining.

The Sierra Fund report found that several recreational trails in the Sierra Nevada foothills had high levels of hazardous contaminants. Long ago, miners pounded rock into dust heavy with lead and asbestos. Water cannons were also used to blast soil off of mountains, and then used mercury to extract gold.

That residue is now stirred up by hikers, mountain bikers and off-road-vehicle riders on popular recreation trails that are routed through old mines, mine tailings and waste rock. The leftover mercury has also washed into rivers and reservoirs, posing a risk for anglers and others who eat sport fish.

“People involved in dusty activity are at the most risk for exposure, either by inhaling it or absorbing it [through the skin],” Monohan said.

Due to limited resources, Monohan’s report focused on recreation trails near Nevada City, Downieville and Foresthill. Although some trails had no problems, others had high levels of contaminants. The report found that Gracie Mine, Banner Mountain and Manzanita Diggings had high levels of arsenic, and Newtown Ditch had high levels of chromium. At Foresthill, the Marall Chrome Mine pit popular with ORV users had off-the-charts levels of arsenic and lead.

“This is a small slice of a much bigger picture,” said Bill Haigh, manager of the Folsom field office of the federal Bureau of Land Management. “There are a lot of old mines that have to be cleaned up.”

In California alone, there are more than half a million abandoned mines.

The BLM, the California Department of Toxic Substances Control, the U.S. Forest Service and local jurisdictions are involved in the cleanup efforts—a long list of agencies that illustrates the size and complexity of the issue.

The DTSC, for instance, partners with water boards to clean up mines with elevated levels of heavy metal and acid mine drainage. However, DTSC spokeswoman Charlotte Fadipe said in an e-mail that abandoned mine sites on federal lands would typically be overseen by the respective federal agency.

Haigh said his BLM field office is working with local jurisdictions and other agencies at sites north of Nevada City, through the Mother Lode Country and down to Mariposa.

“We are trying to find smaller sites and jump right on them,” he said.

John Heil, a spokesman with the U.S. Forest Service, said the federal agency is securing grant funds to help with cleanup. He added that the Forest Service posts warning signs at site headquarters and on bulletin boards, though he didn’t know if the signs were multilingual.

For Monohan, such efforts are small steps toward fixing a big problem.

“We don’t to want to exclude people from trails, but we would like to close certain sections and see more visible notices and warning signs,” she said. “These are well-trafficked trails and places people come and play, so there needs to be a bigger response and more resources devoted to it.”