 Near that lake, rocks produced by the rift can be found on the surface of Isle Royale and the Keweenaw Peninsula of the Upper Peninsula of Michigan, northwest Wisconsin, and on the North Shore of Superior in Minnesota and Ontario.Similar rocks are exposed as far south as Interstate Park near Saint Paul, Minnesota, but elsewhere the rift is buried beneath more recent sedimentary rocks up to thick.Where buried, the rift has been mapped by gravity anomalies (its dense basaltic rock increases gravity locally),
aeromagnetic surveys, and seismic data.