Issues

Cover: Michigan's tallest waterfall, Houghton-Douglass Falls, cascades 110 feet (34 m) over Mesoproterozoic basaltic lavas of North America's Midcontinent Rift System. Older Portage Lake Volcanics at the falls have been thrust over softer younger Jacobsville Sandstone along the Keweenaw fault, which extends along the entire Keweenaw Peninsula where such waterfalls are common. Flows and interflow sedimentary layers in the hanging wall host native copper deposits, once the main source of copper for the United States. Attractive building stone from durable parts of sandstone in the footwall was used in construction throughout the Eastern United States, including the famed original Waldorf-Astoria Hotel in New York City. See “Detached structural model of the Keweenaw fault system, Lake Superior region, North America: Implications for its origin and relationship to the Midcontinent Rift System” by DeGraff and Carter, p. 449–466.

Photo by: Alexis Dahl.