Olmsted said the ice rocks were scattered along a 100-foot stretch of beach. Some weighed as much as 75 pounds, she estimated. "I have a small English bulldog and they were as tall as her. They were pretty massive."
Park Rangers at Sleeping Bear Dunes said the boulders likely broke away from the ice floes that form over Lake Michigan. Waves and wind smooth the chunks of ice into round balls, which can eventually wash ashore, park officials said.
Olmsted told The Weather Channel, "Most of the people who've lived here their whole live said they've never seen anything like it either. So it's really cool."
Florida bear attack: Black bear mauls woman's face
Texas principal bans speaking Spanish, stirs controversy