In 1926, at the region's peak of production, Ottawa County was the largest source of lead and zinc in the world. By the 1960s most of the mines had closed, leaving mine shafts, sinkholes, chat piles, and other dangers for future cleanup. Such areas have been designated as part of the Tar Creek Superfund Site by the US Environmental Protection Agency. Tripoli, primarily used as an abrasive, was found near Peoria in 1912, and was mined into the twenty-first century.
In 1926, at the region's peak of production, Ottawa County was the largest source of lead and zinc in the world. By the 1960s most of the mines had closed, leaving mine shafts, sinkholes, chat piles, and other dangers for future cleanup. Such areas have been designated as part of the Tar Creek Superfund Site by the US Environmental Protection Agency. Tripoli, primarily used as an abrasive, was found near Peoria in 1912, and was mined into the twenty-first century.