The Okotoks Erratic is the largest rock in what?s known as the Foothills Erratic Train. The Foothills Erratic Train is essentially a group of rocks that were fallen here as the glacier melted after being transported by ice along the mountain front some 10,000 years ago. Also known as "The Big Rock", the Okotoks Erratic is the world?s largest glacial erratic. By definition, a glacial erratic is rock that is transported far from its origin by glacial ice. The Okotoks Erratic is one of plenty that lie in a narrow band from northern Montana up to Jasper National Park. "The Big Rock" is a large landmark that looks misplaced in the flat prairies and with time, has been eroded into pieces.

The Okotoks Erratic is said to most likely be from Mount Edith Cavell in Jasper National Park. In present day Athabasca River valley some 18,000 years ago, a rockslide brought rock material and other sediments to the surface of a glacier and the erratic was slowly carried on the back of the glacier as the glacier moved eastwards. Of course this was a slow process that took thousands of years for the glacier to move to the plains where it then collided with the great Laurentide ice sheet, another continental glacier. The Athabasca River valley glacier was then diverted becoming parallel to the mountain front, towards the southeast and is the reason why the erratics were deposited as a narrow band from Jasper National Park to Montana as the ice melted.

As you walk toward the large erratic, you can clearly see the large split in the middle of the rock. On one of the interpretive signs, there is a story stemming from the Natives, specifically the Blackfoots, of how the Okotoks Erratic came to split. The story provides a curious explanation to why bats have faces that look as though they have been squashed as well. It is a good tale with a moral lesson and even caution of taking back what you have given away. The name of the erratic was originated from the Blackfoot word for rock, "okatok".

?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 neighbours, 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.?

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The Okotoks Erratic measures 41m long, 18m wide and 9m high and weighs in at 16,500 tons. Looking closely at the rock, you can see that the rock originates from the Gog formation because of the hardened layers of small pebbles, sand and silt. The Gog formation was found to be in a shallow sea and consisted of the layering of sediment that was deposited roughly 570 to 540 million years ago before the uplift of the Rocky Mountains. It is due to this that the composite of the rock is predominantly quartzite. With time passing on, layer upon layer of sediment was built up thousands of feet thick. The weight of the overlying sediments created heat and pressure and compacted the sand grains. They were then cemented into the durable and extremely hard rock aka quartzite. As the Rocky Mountains were being formed 150 to 50 million years ago, beds of sediment were thrust up and eastwards. In the main ranges of the Rocky Mountains, quartzite is commonly found.

Quartzite is a slippery rock, probably one of the reasons why it is enclosed so that people do not go touch it. There are also pictographs that are slowly fading on the rock and the oils on our hands cause the pictographs to fade away along with natural processes and erosion. Please enjoy the natural formation and refrain from touching the pictographs so others may enjoy the history of this "Big Rock".

Driving along Highway #7, it is hard to miss the rather large, greyish rock lying in the middle of the flat prairies. The Okotoks Erratic is located 10 km southwest of Okotoks

Okotoks Erratic - "The Big Rock" Photos


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