Interior view of the Treadwell foundry. According the Treadwell Historical Society, cauldrons for pouring molten iron-ore into a variety of castings were needed at the Treadwell Complex. The foundry was built in 1909 and was one of the most up-to-date institutions of its kind on the Pacific Coast. Iron ore used as feed was imported from Mesabi Range iron mines in Michigan.
Today, iron ore used in the foundry can still be found piled adjacent to the trail leading past the pyritic tailings at the Mexican Mine, on the Treadwell Trail at Sandy Beach. The foundry was operational after the final Treadwell closure in 1922, making parts for the Alaska Juneau Mine located across Gastineau Channel.