In an otherwise feature-less field, just south of Calgary’s sprawling metropolis, sits an object so out of place from the rest of its surroundings it’s almost as though it was dropped from the sky. The Okotoks Erratic, better known as the Okotoks Big Rock, is a massive quartzite block that weights roughly 16,500 tonnes. Surrounded by rolling prairie, it would be easily assumed that this boulder was an alien rock from outer space. But with the absence of any impact crater, this unusual stone appears to have been gently placed on the Earth’s surface as opposed to crashing into it. The Okotoks Big Rock did not arrive from beyond our galaxy, in fact it originated from somewhere within the Athabasca River Valley in what is modern-day Jasper National Park.
The Big Rock is a glacial erratic, a name given to all rocks that have travelled many kilometres from their original locations on the surface of a glacier. Somewhere between 10 and 18 thousand years ago there was a landslide that dumped an untold amount of debris on top of a glacier. The glacier then carried this accumulation of rock southward towards northern Montana. As the glacier slowly receded, it deposited the rocks across the landscape. The rocks were abandoned in a narrow strip along the foothills that extends for 930 kilometres between Jasper and Montana’s northern border. This slender band is known as the Foothills Erratics Train and contains thousands of rocks and boulders of varying sizes, with the largest being the Okotoks Big Rock.
The rock stood out from the surrounding flat prairie, which made it visible from great distances. Early First Nation groups used the boulder as a landmark to find the crossing over the Sheep River. The rock and surrounding area both have great cultural significance to the Blackfoot People. At one time there were dozens of pictographs painted across the rock’s surface, but time, weather, and vandalism have all but removed them. If you know where to look you can still see some of the faded rock art, but they are very difficult to decipher. Okotoks even takes its name from the Blackfoot Word for rock, ‘okatok’, which could be in reference to the town’s proximity to the erratic.
The Big Rock, like many of the rocks in the Foothills Erratic Train, is fractured down the middle. Geologists attribute this to natural processes, but there’s a Blackfoot story from the 1800’s that offers a different explanation. The story was recorded by George Bird Grinnell and goes like this,
“One hot summer day, Napi – the supernatural trickster of the Blackfoot – sat upon the Rock to rest. Because it was so hot, Napi threw his robe over the Rock saying, ‘Here, I give you my robe, because you are poor and have let me rest on you. Keep it always.’ Napi walked on, and it began to rain. Napi sent to the Rock and asked it to lend him the robe, but the Rock refused. Napi got angry, and took ‘his’ robe. As he walked away, he heard a loud noise – the Rock was chasing him! Napi was scared and ran. His friends – the buffalo, the deer, and the antelope – tried to stop the Rock, but were crushed. Nearly exhausted, Napi called upon some bats for help. The bats dove at the Rock and one hit it in the middle and split it in two. This Blackfoot legend reveals not only how the Rock was split, but also why bats have “squashed” faces. There is also a moral: Don’t take back what you’ve given!”
In 1978 the Government of Alberta declared the Okotoks Erratic as a Provincial Historic Resource in order to protect both its geological and cultural importance. The Big Rock is easily visited today with a short drive from Calgary. There is a parking lot, complete with bathrooms, and the trail to the rock is accessible to everyone via a paved ramp and then a well-graded packed gravel trail. The erratic is roped off, but that hasn’t stopped many people from crossing the barricade and climbing all over it. Please respect the site, and the ancient artwork, but avoiding the temptation to scale this natural feature.