Peninsulas are found all around the world; in the United States, two prominent examples are the Upper Peninsula in Michigan and the Delmarva Peninsula in Maryland. Peninsulas are chunks of land that are surrounded on three sides by water and joined to larger bodies of land by a neck, called an isthmus. Peninsulas occur primarily along ocean coastlines, although they appear along large river borders too.
The Upper Peninsula in Michigan is bordered on the north by Lake Superior while the St. Marys River lies to the east. To the southeast of the Peninsula are Lake Michigan and Lake Huron; the state of Wisconsin lies to the southwest. The Upper Peninsula is unique in that, unlike many peninsulas, its inhabitants have not historically lived in physical, social and geological isolation from inhabitants of the mainland. Nevertheless, the sense of community among residents is quite strong. The physical composition of the Upper Peninsula is similar to that of southern Canada; here there are large tracts of forests and lowland plains, along with a myriad of rivers and waterways. Logging is the primary economic driver in the Upper Peninsula, and tourism follows closely behind. The Delmarva Peninsula forms the eastern portion of the Chesapeake Bay in Delaware, and it formed several million years ago when the nearby Susquehanna River eroded an adjacent river valley.