About 7 km west of the town of Okotoks in Alberta, in Canada, on the flat prairie lies a massive piece of rock 41 meters long, 18 meters wide and 9 meters high, and weighs 16,500 tons. It’s a glacial erratic - a rock transported far from its place of origin by glacial ice thousands of years ago. The Okotoks Erratic, also known as “the Big Rock” is the world's largest known glacial erratic. In fact, the name of the town – Okotoks – is itself derived from the word “ohkotok” which means “rock” in the Blackfoot language.

The rock is one of several thousand erratics found in Alberta and Montana lying along a narrow band extending from Jasper National Park to northern Montana called the Foothills Erratics Train. The erratics train originated from a landslide in the Tonquin Valley of Jasper National Park, and was transported along the confluence of the Cordilleran Ice Sheet and the Laurentide Ice Sheet approximately 12 to 18 thousand years ago to its present location.

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During the last ice age, sometime after about 30,000 years ago, a large rockslide crashed debris onto the surface of a glacier that occupied the present day Athabasca River valley. This debris, including Big Rock, rode on the back of the glacier as the ice moved eastwards to the mountain front, where it collided with a huge continental ice mass, the great Laurentide ice sheet. The Athabasca River valley glacier was then deflected to the southeast becoming parallel to the mountain front. When the ice melted, the erratics were left behind.

The Big Rock has a large split down the middle. The natives of the Blackfoot First Nation has an amusing story that not only explains why the rock is in two pieces, but also why bats have squashed-looking faces. The legend goes,

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.

The Big Rock was considered sacred by the people of the First Nations and a large number of Aboriginal rock art is painted on its surface.

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Graffiti and vandalism on the Big Rock. Photo credit

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Sources: Wikipedia / Alberta Culture and Tourism