[1][2] It is about 30 kilometers (19 mi) thick and it formed about 1.1 billion years ago.
[3] Members of the Keweenawan Supergroup are exposed at the surface only in the Lake Superior region, particularly at the perimeter of the Midcontinent Rift System.
To the southeast and southwest, they are covered by sedimentary rocks of Paleozoic age.
[1] The supergroup consists of the following members:[2] The Powder Mill Group is reversely polarized except for intervals at the base and top of the upper Kallander Creek Volcanics.
[4] The Portage Lake Volcanics and all younger formations have normal magnetic polarity.