Castle Rock, about three miles north of Saint Ignace near the Straits of Mackinac, is a limestone stack rising 195.8 feet above nearby Lake Huron and ranks among the Upper Peninsula’s best-known natural landmarks. Formed through long erosion after the Wisconsinan Glaciation, it survived as surrounding land was worn away when postglacial Lake Algonquin stood higher and then receded, leaving a steep isolated mass of resistant limestone breccia. Geologically akin to formations on Mackinac Island, it also became a notable roadside attraction. Since C. C. Eby opened it to the public in 1928, it has remained a seasonal tourist stop operated by the Eby family.