Fifty miles off the shore of a northern Michigan town, John O’Shea and his crew lowered a sonar device 120 feet beneath Lake Huron in search of ancient landmarks.

The process has become somewhat routine for O’Shea, who has explored the Great Lakes for more than three decades.

“For us, archaeology is a long, grinding accumulation of information,” said O’Shea, Emerson F. Greenman Collegiate Professor of Anthropological Archaeology at the University of Michigan. “You very rarely get an ‘aha moment’ where something appears right beneath you.”

On this particular day, however, O’Shea and his crew experienced their ‘aha moment’ when sonar revealed a 9,000-year-old caribou hunting structure hidden along the lake bottom.

“We just sat there with our mouths wide open because this is what it looks like in the movies,” said O’Shea, also curator of Great Lakes Archaeology at the U-M Museum of Anthropological Archaeology, who monitored underwater footage aboard his boat. “It almost never works this way in practice. Holy cow. It was just mind blowing.”