"The Big Rock" is the world's largest known glacial erratic--rock transported far from its place of origin by glacial ice. Big Rock, also known as the Okotoks Erratic, is the largest rock in the Foothills Erratics Train, a group of rocks that were carried by ice along the mountain front and dropped as the glacier melted some 10,000 years ago. The erratics lie in a narrow band extending from Jasper National Park to northern Montana. The Okotoks Erratic weighs 16,500 tons. It measures 9 metres high, 41 metres long and 18 metres wide. The rock has been eroded into pieces, but is still a large landmark on the flat prairie.