Arch Rock is a geologic formation on Mackinac Island ( link ) in Michigan ( https://en.wikipedia.org/wiki/Michigan ). It is a natural limestone arch ( link ) formed during the Nipissing post-glacial period, a period of high Lake Huron ( https://en.wikipedia.org/wiki/Lake_Huron ) levels following the end of the Wisconsin glaciation ( link ). To this day Arch Rock stands on the Lake Huron shoreline 146 feet (45 m) above the water.