Big Rock is located 7 km west of Okotoks. It measures 40 metres by 18 metres by 9 metres, and weighs 18000 tons. Big Rock is North America's largest glacial erratic. Big Rock is the biggest among thousands in a 644 km chain called the Foothills Erratic Train.

First Nations Pictographs can be seen near the top of Big Rock. The depression around the rock was created by Plains Bison, which used the rock as a rubbing stone. The Stitt family, who once farmed on the Big Rock property, had to fence a crevice of the Big Rock after finding the bones of their lost cows there.

On May 16, 1978, the Big Rock was the first natural feature to become an official Provincial Historic Site under the Alberta Historical Resources Act.

According to Blackfoot legend, one of the first people to live in this area was Napi (The Great Spirit), a warrior of great courage. Napi was strolling through what is now Waterton National Park in southwest Alberta. Along the way, he loaned his coat to a large rock, but later sent a coyote to retrieve it. When the rock refused to hand over the garment, Napi went back and seized it.

Enraged, the Rock chased Napi across the prairie. Fearing for his life, Napi sought the aid of his animal friends. Flocks of birds descended, chipping away at the rock, until finally a nighthawk struck it and it fell dead where it is today. For generations, native tribesman approached Big Rock respectfully and deposited gifts for the Great Spirit at its base.

Today, these boulders are one of the interesting landscape features of Alberta.