Recreational Trails and Abandoned Mines Assessment

The Sierra Fund conducted a study in 2009-10 to learn whether a public health threat existed on trails that passed through abandoned mine sites.  We took soil samples from trails and learned that while some areas posed little problem, in other areas exposure potential to lead, arsenic and other toxins is high.  Click here to read the full text of the study which was released in 2010, or the 2-page executive summary is available here.


One hundred fifty years of mining in the Sierra Nevada left their mark. Today, the region is riddled with abandoned mine shafts and tunnels—and other dangers may not be apparent at first glance.

Of particular concern are heavy metals and minerals that arise with gold; particularly naturally occurring arsenic, lead, chromium and asbestos, which people may be exposed to by breathing dust. Historic mining activities made these toxins much more available for human exposure by crushing the rocks, and distributing them over the surface.

In addition, roads were constructed to access the mine sites, and many are still used for travel and recreation today. The main exposure route is through breathing dust.

Project-Buttons_trailssamplingStudy Efforts

In 2009, The Sierra Fund completed a study to determine if recreational hikers, mountain bikers, horseback riders, and off-highway vehicle (OHV) riders may be exposed to high levels of these toxins at abandoned mine sites. To learn this, popular trails in the Downieville, Nevada City, and Foresthill areas were mapped with GIS, and known abandoned mine sites were mapped over the trails.  Sites of concern were identified where an abandoned mine was within 30 feet of the popular trail. Soil samples were taken at sites of concern, and sent the samples to labs for analysis.

High levels of lead and arsenic were found in the Forresthill, Downieville, and Nevada City areas, while high levels of arsenic were found in Downieville and Nevada City. The most serious problem was found at the Foresthill OHV Area. In this designated recreation area on Forest Service land, families were riding OHVs on soil containing up to 40% asbestos fibers, as well as off-the-charts levels of lead.

Based on our 2009 study, The Sierra Fund recommended that clear, visible advisories be posted in areas of known to be contaminated by toxic substances.

See also:

Full text of the Gold Country Recreational Trails and Abandoned Mines Assessment including maps, methods, lab results, all findings, and recommendations

Executive Summary of the study, which includes key findings and recommendations

Gold Country Angler Survey – A study The Sierra Fund has been conducting since 2010 to look at exposure potential to mercury through eating locally caught fish

Health Outreach Program – The Sierra Fund’s campaign to bring information about public health exposures to legacy mining toxins to rural Sierra communities, and the doctors and nurses who serve them