This enormous quartzite block, weighing about 16,500 tonnes and measuring about 41 x 18 x 9 metres, was carried here on the surface of a glacier. It came from the Rocky Mountains in the Jasper area, probably between 18 and 10 thousand years ago. Rocks moved many kilometers from their original location by the ice are called 'glacial erratics'.
Big Rock began its journey when rockslides in the mountains deposited quartzite debris onto the top of a glacier in the Athabasca River valley. The glacier carried the rocks with it as it flowed slowed eastward to the plains, until it collided with the Laurentide ice sheet. This massive ice sheet deflected the glacier to the southeast, parallel to the mountain front. When the ice melted, a string of erratics was left in a narrow belt extending from Jasper National Park along the foothills to northern Montana. This group is known as the Foothills Erratics Train, and the Okotoks Erratic is the largest member.
The name of the rock was derived from the Blackfoot word for rock: okatok.