Fog rolls off of Lake Superior and up the Grand Sable Dunes on the Pictured Rocks Lakeshore as seen from the Log Slide Overlook west of Grand Marais in the Upper Peninsula of Michigan. The Grand Sable Dunes are located on a five mile stretch between the Sable River and Au Sable Point in Alger County. The banks rise up to 275 feet high, created during the last ice age when sand and gravel filled in a deep rift in the glacier. Atop the gravelly banks, sand dunes rise another 80 feet. These are "perched dunes" because they are perched on top of another landform. They were probably formed when wind and waves piled up sand at the edge of Lake Nipissing, the forerunner of Lake Superior.