The Foothills Erratics Train is a 580 miles (930 km) long, narrow, linear scatter of thousands of typically angular boulders of distinctive quartzite and pebbly quartzite that lie on the surface of a generally north-south strip of the Canadian Prairies. These boulders, which are between 1 foot (0.30 m) and 135 feet (41 m) in length, are glacial erratics that lie upon a surficial blanket of Late Wisconsin glacial till. The largest glacial erratic within the Foothills Erratics Train is Big Rock.

A glacial erratic is a glacially deposited rock differing from the type of rock native to the area in which it rests. Erratics, which take their name from the Latin word errare, are carried by glacial ice, often over distances of hundreds of kilometres. Erratics can range in size from pebbles to large boulders such as Big Rock in Alberta.