A page about the Point Aux Barques – Turnip Rock geocache had the best information I found about this Lake Huron Landmark. The author explains:
This cache is accessible by a kayak, canoe, jet ski or boat on Lake Huron. Port Austin is the closest harbor which is approximately three miles west. The land around this feature is a gated community. I must stress that this cache is only accessible by a water craft via Lake Huron. If you are not comfortable navigating the waters of Lake Huron, do not attempt to do this cache. Lake Huron can be dangerous at times for small water craft such as kayaks or canoes.
…Everyone that received their grade school education in Michigan learned that glaciers pushed their way over Michigan several times. The result is glacial drift averaging 200 to 300 feet deep covering on top of the bedrock. The thickness of drift has measured over 1,000 feet in a few Michigan locations. Rarely can we see exposed bedrock that has been sculptured by non glacier forces. This is one of the locations in southern Michigan where the sandstone bedrock is exposed at the surface. The amount of shoreline that has exposed sandstone is about one mile, but a lot of beauty has been sculptured in the stone.
The locals call the main structure here “Turnip Rock”, because of it’s shape. Geologists call it a “Sea Stack”. A definition of a sea stack is an isolated pillar-like rocky island or mass near a cliff shore, detached from a headland by wave erosion assisted by weathering. Waves force air and small pieces of rock into small cracks, future opening them. The cracks then gradually get larger and turn into a small cave. When the cave wears through the headland, an arch forms. Further erosion causes the arch to collapse. This causes a pillar of hard rock standing away from the coast. Generally occurring in sedimentary rocks, sea stacks can occur in any rock type.
Read on for more and also see the Atlas Obscura entry for Turnip Rock has a map and photos. Michigan in Pictures favorite Lars Jensen has some great photos of Turnip Rock as well, and you should definitely check out Jason Glazer’s panoramic photos of Turnip Rock.
More Michigan landmarks on Michigan in Pictures.