Big Rock (also known as either Okotoks Erratic or, by the Blackfoot Indians, as Okotok) is a 16,500-tonne (18,200-ton) boulder that is about the size of a two-story house and lies on the otherwise flat, relatively featureless, surface of the Canadian Prairies in Alberta. It is part of the  Foothills Erratics Train of typically angular boulders of distinctive quartzite and pebbly quartzite.