The site includes many old silver and lead mines that were most active between 1879 and 1920.
Little mining is conducted at present.
The primary concern is toxic metals contained in mine wastes, mill tailings, and smelter by-products. A potential health hazard exists through direct contact and airborne, waterborne, or food-chain exposure to the high concentrations of toxic metals, especially lead. An EPA site investigation found elevated concentrations of cadmium, copper, and zinc in wells near the site. High concentrations of toxic metals, including more than 20,000 parts per million of lead, have been measured in the soils and tailings on the site. Previously, investigators at the Colorado State University Extension Service measured high concentrations of lead in leafy green vegetables grown in contaminated soils.