The boulder with the markings is 3.5 to 4 feet high and about 5 feet long. Photos show a surface with numerous fissures. Some may be natural while others appear of human origin, but those forming what could be the petroglyph stood out, Holley said.
Viewed together, they suggest the outlines of a mastodon-like back, hump, head, trunk, tusk, triangular shaped ear and parts of legs, he said.
"We couldn't believe what we were looking at," said Greg MacMaster, president of the underwater preserve council.
Specialists shown pictures of the boulder holding the mastodon markings have asked for more evidence before confirming the markings are an ancient petroglyph, said Holley.
"They want to actually see it," he said. Unfortunately, he added, "Experts in petroglyphs generally don't dive, so we're running into a little bit of a stumbling block there."
If found to be true, the wannabe petroglyph 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. The formation, if authenticated, wouldn't be completely out of place. Stone circles and other petroglyph sites are located in the area.
The discovery was made back a few years ago, and surprisingly enough the find hasn't been popularized at all, with little to no information available online, but I'll be sure to update this post as soon as I can get a hold of more info. So, who's from Michigan?