Canadian Rockhound: The Foothills Erratics Train

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The Foothills Erratics Train
By Murray Nicholson

Scattered on the plains in front of the Rocky Mountain Foothills are tens of thousands of large boulders, the extraordinary remains of the ice age in Alberta. These pinkish or purplish quartzite boulders are part of the Foothills Erratics Train, a narrow area extending 600 kilometres southeast from Jasper National Park to the international border.

According to the current theory, the Foothills Erratics Train originated towards the end of the last ice age when a landslide similar to the Frank Slide dropped millions of tons of rock onto the surface of a glacier, near the town of Jasper. The glacier carried the rock out of the mountains into the foothills where it was deflected toward the southeast by the edge of the continental glacier. The boulders were deposited in their present pattern as movement ceased and the glacier eventually melted.

One erratic, called Split Rock, can be found on the northern edge of Calgary, where Centre Street crosses Beddington Creek. The largest of the foothills erratics, called Big Rock, is located in the middle of a field, a few kilometres west of Okotoks. Above the ground, this rock measures about 45 x 20 x 10 metres and is estimated to weigh over 18,000 tons. The ice sheet which carried it to this location would have been at least 60 metres thick and 180 metres wide.

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

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The preceding article was first published in the October 1991 issue of the Calgary Lapidary Journal, the official newsletter of the Calgary Rock & Lapidary Club. Updated April 23, 1997. Reprinted in the Canadian Rockhound with permission from the author and editor.