Lake Superior islands include Madeline Island in the state of Wisconsin, Michipicoten Island in the province of Ontario, and Grand Island (the location of the Grand Island National Recreation Area) in the state of Michigan. The larger cities on Lake Superior include the twin ports of Duluth, Minnesota and Superior, Wisconsin; Thunder Bay, Ontario; Marquette, Michigan; and the twin cities of Sault Ste. Marie, Michigan, and Sault Ste. Marie, Ontario. Duluth-Superior, at the western end of Lake Superior, is the most inland point on the St. Lawrence Seaway and the most inland port in the world. Among the scenic places on the
Duluth, Minnesota sandy core. As the last glacier retreated, meltwaters filled the lake to as high as 500 feet above the current level; the Skyline Parkway roughly follows one of the highest levels of the ancient Lake Superior, Glacial Lake Duluth. The sandstone that buried the igneous rocks of the rift is exposed near Fond du Lac. At one time a large number of quarries produced the stone, sold as Fond du Lac or Lake Superior brownstone. It was widely used in Duluth buildings and also shipped to Minneapolis, Chicago, and Milwaukee, where it was also used extensively. The weathered sandstone forms