Beneath the calm waters of Grand Traverse Bay lies a secret older than any known shipwreck. While the bay has long been associated with smooth sailing and maritime history, a recent discovery is shifting focus to a much earlier era. Divers have uncovered plenty of sunken ships over the years—but none as ancient or mysterious as this.

During a routine sonar sweep, Dr. Mark Holley, an underwater archaeology professor at Northwestern Michigan College, detected something unexpected: a series of massive stones arranged in a deliberate pattern on the lakebed. Nicknamed “Michigan’s Stonehenge,” the formation is capturing new interest in the region’s prehistoric past.

Roughly 40 feet underwater, the stones stretch in a winding formation for more than a mile. Though not as large as its English namesake, the layout appears intentionally constructed. The stones vary in size—from basketball-like to compact car–sized—and form a twisting path that experts say nature couldn’t have made on its own.

One stone stands out in particular: a 3.5-foot-tall slab bearing what appears to be a carved mastodon, an Ice Age giant. This carving suggests the site dates back to a time when humans and mastodons coexisted—a rare glimpse into ancient life and early cultural expression in North America.

Archaeologists estimate the structure was built around 9,000 years ago, just after the last Ice Age, when the bay’s waters hadn’t yet submerged the area. That would make it some 4,000 years older than Stonehenge, placing it in the early Holocene and offering a tantalizing clue to the lives of North America’s earliest inhabitants.