The surface of the Keweenaw Peninsula and Isle Royale was covered by continental glaciers for millions of years until about 10,000 years ago. During this time as much as two miles of ice buried Houghton. The ice came from the northeast and moved across the rock surface eroding deeply into the earth. As this happened, copper from veins within the lavas and conglomerates were occasionally freed from their surrounding rock, forming a “floating” piece of nearly pure copper. Often these float coppers were buried inside glacial outwash deposits like those right here on the MTU campus and all around Houghton and Hancock at Coles Creek and the Hancock Gravel Quarry.
The First Nation people found copper boulders like this one beginning as long as 9000 years ago, and traded the precious metal all over North America.
The most famous piece of float copper in the region is the Ontonagon Boulder, a legendary boulder found along the riverbank south of Ontonagon. The boulder had a repute that extended to many people from First Nation to immigrants and industrialists--it is a geoheritage icon. It was annexed by the US Army and taken to the Smithsonian Institution where it has been kept for more than a century.
