Is it a peninsula or an island? It seems to me its an island because its separated by a natural waterway, though it was small until it was dredged in the 1860s. So sometimes the northern part of the peninsula is called "Copper Island." But mostly the whole thing is called Keweenaw Peninsula.
While the upper Michigan peninsula has lots of iron mines, copper was found in quantity and mined only on the Keweenaw Peninsula. How did it get there? About 1.1 billion years ago, the Midcontinent Rift developed in the North American Plate. The rift failed, and the plate did not split. Keweenaw Peninsular was probably the location of a hot spot at a three-way junction in the 2000-mile-long rift. The hot spot made a dome that covered the area that now holds Lake Superior. Magna filled in as the rift developed. Most of the rift's igneous rocks are deeply buried (about 6 miles down), but they are relatively near the surface at the Keweenaw Peninsula. The copper formed was 97 percent pure native copper--the biggest formation of native copper that has been found in the world. (Most copper ore is only 1-2% copper). Here is picture I took of a sheet of copper mined from the Keweenaw Peninsula. It is on display in the National Museum of Natural History in Washington, DC:
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| Native Copper Sheet Approximate Size 10 ft by 4 ft Mined from Keweenaw Peninsula, Upper Peninsula Michigan |
Mileage: 425. Cumulative mileage: 7,850.
