Iron Mountain: An Extraordinary and Extreme Environment

Science Center Objects

At its peak production, Iron Mountain ranked as the tenth largest copper production site in the world, sixth in the U.S. and first in California. During its operation, from 1879 - 1963, ten different mines throughout the site's 4,400 acres were the source of not just copper, but also silver, iron, gold, zinc and pyrite (iron sulfide).

A century of active mining at Iron Mountain took an environmental toll. The first documented consequence of mining was fish kills in the Sacramento River in 1899, followed by severe air pollution from the open-air heap roasting and smelters that stripped the land of vegetation near the town of Keswick along lower Spring Creek. As mining operations increased, so did pollution. Acid mine water seeping into the Sacramento River, sizable fish kills, and sediment deposits in the Spring Creek Arm of Keswick Reservoir have all plagued the area. To compound the issue, the city of Redding receives its drinking water from the Sacramento River, downstream from the Iron Mountain site. An uncontrolled release of Iron Mountain acid mine drainage could potentially threaten the quality of the drinking-water supply.


red water flowing in a very rocky streambed

Acid mine draining flowing in a stream near the Iron Mountain mine in northern California near Redding. Acid mine drainage (AMD) is metal-rich, acidic water that is the result of water from mining activities flowing over or through rocks containing pyrite, a sulfur bearing mineral. This water reacts with pyrite and air to form sulfuric acid and dissolved iron. The chemical reactions that form AMD are sped up greatly by the activity of iron- and sulfur-oxidizing microbes, including bacteria and Archaea (formerly known as archaebacteria). AMD also further dissolves other heavy metals that are present at Iron Mountain (copper, zinc and cadmium) into ground or surface water. (Public domain.)


In 1983, the site was one of the first listed on the U.S. Environmental Protection Agency's National Priority List as part of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or "Superfund"). Its ranking was the third most hazardous site in the State of California. Several successive studies recommended remedial measures to clean up contamination sources at the Iron Mountain site. Starting in 1986, the EPA authorized four Records of Decision (RODs) that enforced specific clean up tasks, such as partial capping, surface-water diversions, tailings removal, and lime neutralization treatment of the most acidic, metal-rich flows, which have reduced copper and zinc loads by 95%.

For further information, see:

Geology and Mining History 

Environmental Effects

Timeline of Mining and Remediation History

Pipe Scale Study

As acidic water at Iron Mountain is transported away from inactive mining sites to a treatment plant, microbial oxidation causes iron in the acid mine drainage to accumulate on the inside of the pipeline, resulting in pipe scale. The encrusted pipes interfere with treatment efforts and cause costly management problems when pipe-scale buildup clogs pipelines and other treatment structures. USGS scientists are working with the EPA to research strategies to prevent or retard scale formation in the pipeline.

Pipe Scale Studies At Iron Mountain Mines >>


Significance of Sulfates

Sulfide oxidation at Iron Mountain has led to extremely acid mine drainage and the active formation of a wide variety of iron-sulfate minerals, including phases identified on Mars. The presence of these sulfates has provided a unique opportunity for scientists to sample associated waters, evaluate water-mineral equilibria, and understand microbes living in these extreme conditions.

Sulfate Minerals at Iron Mountain >>


Connections to Mars Research

The mineralogy at Iron Mountain can serve as a proxy for understanding the formation of iron oxides and sulfates on Mars. The extreme conditions at Iron Mountain provide a unique setting that has allowed significant scientific advances to be made in environmental geochemistry, mineralogy, microbiology, and Mars analog studies.

Iron Mountain and the Red Planet >>