"Stonehenge Beneath the Waters of Lake Michigan" -

In a surprisingly under-reported story from 2007, Mark Holley, a professor of underwater archaeology at Northwestern Michigan University College, discovered a series of stones – some of them arranged in a circle and one of which seemed to show carvings of a mastodon – 40-feet beneath the surface waters of Lake Michigan.
If verified, the carvings could be as much as 10,000 years old – coincident with the post-Ice Age presence of both humans and mastodons in the upper midwest.