Ontonagon

River in Michigan's northwestern upper peninsula, USA; 35 km/22 mi in length. Formed by the confluence of East, Middle, South, and West branches, which flow through the Ottawa National Forest, it empties into Lake Superior at Ontonagon, the seat of Ontonagon County.

The Ontonagon Boulder, first seen by Europeans in the 1660s, was a huge block of very pure copper that led many to think the area was rich in ore. Mining, begun seriously in the 1840s, did not succeed, and the Ontonagon region became a lumber producer, particularly for matchwood. However, the story of the boulder served to bring prospectors into the Porcupine Mountains to the south, and these later became a productive copper source.