Iron Mountain Mine Iron Mountain Mine (IMM) has been a source of acid mine drainage resulting from over one hundred years of mining activity. Though mining operations were discontinued in 1963, underground mine workings, waste rock dumps, piles of mine tailings, and an open mine pit still remain at the site. Historic mining activity at IMM has fractured the mountain, exposing minerals in the mountain to surface water, rainwater, and oxygen. The exposed minerals form sulfuric acid, which leaches out copper, cadmium, zinc, and other heavy metals. The resulting acidity and the heavy metal contamination have caused the virtual elimination of aquatic life in sections of Slickrock Creek, Boulder Creek, and Spring Creek, tributaries of the Sacramento River. Since 1940, high levels of contamination in the Sacramento River have caused numerous fish kills. The continuous release of metals from IMM has contributed to a steady decline in the fisheries population in the Sacramento River.
Under a settlement of natural resource damage claims arising from the injuries, approximately $9 million will be used for natural resource restoration projects. The settlement also included an option for the United States to acquire without cost 14 tracts of land, to be administered by the U.S. Bureau of Land Management. A Draft Restoration Plan prepared by the IMM trustees, describes proposed restoration actions using the settlement funds and potentially 1,250 acres of land. Proposed restoration actions include enhancing salmonid spawning habitat, riparian functions, and in stream resources, in the Sacramento River and its tributaries between Keswick Reservoir and Red Bluff.