Apparently there is a Stonehenge on the floor of Lake Michigan

And one of the stones has a mastodon carved on it, which died out in North America like 10000 years ago. “They believe that this building, similar to Stonehenge, is about 9000 years old, but interestingly, on one of the stones there is carving in the form of mastodon, which died out more than 10,000 years ago. The exact coordinates of the find are still kept secret – this condition was put by local Indian tribes who do not want the influx of tourists and curious on their land.“