History

The Keweenaw region in Upper Michigan has some of the highest quality copper in the world, being 95-98% pure. There is evidence of hundreds of ancient mines that date between 4,000 - 10,000 BC and that hundreds of tons of copper was removed. But, we have no clear idea what… https://t.co/ngqhfPhdXr

— Josh | Map Effects (@MapEffects) March 9, 2026