And under the main span of the Big Mac bridge is the original river channel. The largest ancient waterfall in the river system was just down stream from there in Lake Huron.
Back abt 10 to 15 thousand years ago, the Great Lakes did not exist as they are today.
There’s been a sudden uptick of interest because Gestapo Gretchen and her stooges want the pipeline work stopped.
https://www.mackinacproperties.com/cave-discovered-near-ancient-waterfall-at-straits