Okotoks Erratic, situated 7 km west of Okotoks, Alberta, Canada, is a supreme example of a glacial erratic. Commonly known as Big Rock, this quartzite boulder is the world's largest known glacial erratic at 16,500 metric tons.
Glacial erratics are often pushed hundreds of kilometers away from their origin by way of glacial movement. As such, erratics provide researchers with the opportunity to study the path of prehistoric glaciers. Tracing an erratic back to its parent bedrock can confirm the route of an ice flow. Researchers believe that Big Rock was transported sometime around 12-18 thousand years ago along the confluence of the Cordilleran and the Laurentide Ice Sheets, two major ice sheets that covered most of North America. Alberta (Canada) and Montana (USA) contain several thousand erratics along what is known as the Foothills Erratics Train.
More recent in its history, Big Rock may have been used as a landmark for the Blackfoot First Nation as "O'kotok" translates to "rock" in the Blackfoot language. The site contains native pictographs, but the date and meaning of these symbols remain unknown.
Big Rock was Alberta’s first natural feature to become a Provincial Historic Site in 1978 under the Alberta Historical Resources Act.