On the riverbed of the Glacial St. Croix River, which was fed the melting ice sheets that were a mile thick over 10,000 years ago, sand and gravel were caught in giant eddies. The action of the swirling rocks wore holes in the hard basalt riverbed and larger rocks that fell into the holes were tumbled and spun until nearly smooth.
This large pothole is called the Lily Pond, since in the early days of the state park, water lilies were planted in the pothole. I didn’t see any lilies in the pothole, although a frog was croaking up a storm, but I think it might need to be renamed Pea Soup Pond instead.
Lily Pond Pothole
