Belt Supergroup

The Belt Supergroup, is an assemblage of Mesoproterozoic sedimentary rocks, primarily mudstones, which outcrop chiefly in western Montana, but also exposed in Idaho, Washington, Wyoming, and British Columbia. It is most famous as the formation that makes up Glacier National Park in northwest Montana. It has been geologically linked to the Purcell Supergroup in British Columbia, rocks of the Udzha Basin in Siberia, and the Rocky Cape Group in Tasmania. It was named after the Big Belt Mountains, Little Belt Mountains and town of Belt, all in western-central Montana.