Okotoks Erratic

A Long and Slow Voyage

Big Rock is the world’s largest known glacial erratic –pushed far from its place of origin by glacial movement. At 16,500 metric tons, this enormous erratic measures about 9 meters high (30 feet), 41 meters long (135 feet), and 18 meters wide (59 feet). Transported over 10,000 years ago, Big Rock now rests in the flat prairies of Alberta, Canada, along the Foothills Erratics Train which extends 644 kilometers, roughly 400 miles, from Jasper National Park in Alberta to northern Montana in the United States.

A Geological Formation

Big Rock, or Okotoks Erratic, is part of the Gog Formation, a geologic formation in Alberta containing fossils of a shallow sea dating back to the Cambrian period. Some areas within this formation can be as thick as four kilometers. Looking closely at the rock, hardened layers of sand, silt, and small pebbles are visible, characteristic of the deep layers of sediment deposited between 600 and 520 million years ago. Through heat and pressure generated by the weight of the overlying sediments, the sand grains were compacted into the hard and durable quartzite we see today.

A Blackfoot First Nation's Tale

Thousands of years ago, Big Rock may have been used as a landmark due to the numerous pictographs found on the Rock and continues to hold spiritual significance to the people of the Blackfoot First Nation today. The name for the erratic comes from the Blackfoot word for rock, “okatok.” One of Big Rock’s unique features is a large split down the middle, separating the erratic into a western and an eastern boulder. A popular Blackfoot story describes how this split may have occurred:

One hot summer day, Napi, the supernatural trickster of the Blackfoot peoples, rested on the rock because the day was warm and he was tired. He spread his robe on the rock, telling the rock to keep the robe in return for letting Napi rest there. Suddenly, the weather changed and Napi became cold as the wind whistled and the rain fell. Napi asked the rock to return his robe, but the rock refused. Napi got mad and just took the clothing. As he strolled away, he heard a loud noise and turning, he saw the rock was rolling after him. Napi ran for his life. The deer, the bison and the pronghorn were Napi's friends, and they tried to stop the rock by running in front of it. The rock rolled over them. Napi's last chance was to call on the bats for help. Fortunately, they did better than their hoofed neighbors, and by diving at the rock and colliding with it, one of them finally hit the rock just right and it broke into two pieces.

Credit: Alberta Culture and Tourism

Preserving the Big Rock

Located just off the highway, Okotoks Erratic is seen by many visitors, and suffers regular damage from vandalism and weather. In order to recognize the site’s geological and cultural importance, as well as to encourage its protection, the Government of Alberta declared Okotoks Erratic as a Provincial Historic Site in 1978 under the Alberta Historical Resources Act. The digital preservation of Okotoks Erratic took place in September of 2013, allowing for a high-detail view into its state of preservation, as well as providing conservation materials for ongoing preservation efforts.


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