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
Lake Superior agate Minnesota industrial mineral found extensively throughout the Iron Range region. Finally, the Lake Superior agate can be found in many regions of Minnesota as it was distributed by glacial movement across Minnesota 10,000 to 15,000 years ago. More than a billion years ago, the North American continent began to split apart along plate boundaries. Magma upwelled into iron-rich lava flows throughout the Midcontinent Rift System, including what is now the Minnesota Iron Range region. These flows are now exposed along the north and south shores of Lake Superior. The tectonic forces that attempted to pull the continent apart, and which