Argillite - Belt Supergroup

Belt Supergroup

The Belt Supergroup of rocks is composed mainly of argillite, as well as other metamorphosed or semi-metamorphosed mudstones. This supergroup is mainly exposed in Western Montana, including the Bitterroot Valley and Bitterroot Mountains, Missoula area, Flathead Lake, and Glacier National Park, and is also exposed in parts of Northern Idaho, and British Columbia. Belt Supergroup rocks are also thought to be present in what is now Korea, Northeast China, and Eastern Siberia as well as possibly Australia. Glacier National Park in northwestern Montana and Wolf Creek Canyon along the US Interstate 15 in west-central Montana are well known for their exposed deep purple, wine red, red, blue, turquoise, and green argillites.