Natural
The ancient lava flows of the Keweenaw Peninsula were produced during the Mesoproterozoic Era as a part of the Midcontinent Rift. This volcanic activity produced the only strata on Earth where large-scale economically recoverable 97 percent pure native copper is found.
Much of the native copper found in the Keweenaw comes in either the form of cavity fillings on lava flow surfaces which has a lacy consistency, or as float" copper, which is found as a solid mass. Copper ore may occur within conglomerate or breccia as void or interclast fillings. The conglomerate layers occur as interbedded units within the volcanic pile.
The Keweenaw Peninsula and Isle Royale, formed by the Midcontinent Rift System, are the only sites in the country with evidence of prehistoric aboriginal mining of copper. Artifacts made from this copper by these ancient Indians were traded as far south as present day Alabama. These areas are also the unique location where Chlorastrolite, the state gem of Michigan, can be found.
The northern end of the peninsula is sometimes referred to as Copper Island (or "Kuparisaari" by the Finnish immigrants), although this term is becoming less common. It is separated from the rest of the peninsula by the Keweenaw Waterway, a natural waterway which was dredged and expanded in the 1860s across the peninsula between the cities of Houghton (named for Douglass Houghton) on the south side and Hancock on the north.
A Keweenaw Water Trail has been established around Copper Island. The Water Trail stretches approximately 125 miles (200 km) and can be paddled in five to ten days, depending on weather and water conditions.
The Keweenaw Fault runs fairly lengthwise through both Keweenaw and neighboring Houghton counties. This ancient geological slip has given rise to cliffs along US 41 and Brockway Mountain Drive north of Calumet.
Read more about this topic: Keweenaw Peninsula
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