The sinkhole country

Some of the strangest land in Michigan sits just north and west of Alpena. This is karst country, where the bedrock is limestone with layers of soft gypsum beneath it. Over thousands of years, water has dissolved that gypsum into hidden caverns, and from time to time the ground above simply collapses into them, leaving deep, steep-sided pits called sinkholes. In a few places whole streams disappear underground here, only to bubble back up from the bottom of Lake Huron miles offshore.

The easiest place to see this for yourself is Rockport, a state park on the Lake Huron shore north of town. It was Michigan’s hundredth state park, and it’s a peculiar and wonderful spot: more than a dozen sinkholes scattered through the woods, one of them over a hundred feet deep, and a vast abandoned limestone quarry where you’re actually allowed to hunt for Devonian fossils and carry some home. Because it’s far from city lights, it’s also a designated dark-sky place, good for stargazing.

Other sinkholes dot the area too, some reachable by woodland trail and some only by kayak. They’re a reminder that in this corner of Michigan, the ground itself has a hidden life. You can plan a visit at visitalpena.com/adventures/sinkholes.