Each hoodoo near Drumheller is a column of dark shale with a harder cap of sandstone resting on top, and the whole arrangement is shrinking by about a centimetre a year. Canada’s Historic Places counts roughly 10 columns on 11 hectares between Drumheller and East Coulee, each between one and three metres tall, with mushroom-shaped tops and horizontal bands that show the layers of the rock. The cap looks like a hat. It is the only thing keeping the shale beneath it standing.
Key facts
- Canada’s Historic Places states that the Hoodoos near Drumheller were recognized as a Provincial Historic Resource on January 25, 2001, and listed on the Canadian Register of Historic Places on February 14, 2008.
- Canada’s Historic Places states that the Hoodoos cover about 11 hectares between Drumheller and East Coulee and hold about 10 stone columns between one and three metres tall.
- Canada’s Historic Places states that the Hoodoos erode at about one centimetre a year.
- Canada’s Historic Places dates the formation to the Cretaceous Period, between 70 million and 75 million years ago.
A soft column survives only while its hard cap holds
The base of each column is dark brown marine shale from the Bearpaw Formation. The cap is harder sandstone and clay from the Horseshoe Canyon Formation. Water, wind and frost strip the shale from everywhere except the ground directly under a cap, and over many seasons that leaves a tower standing while everything around it is carried down the coulee. When a cap slips or wears through, nothing shields the shale below it, and the column goes the way of the ground it once stood above.
The rock is 70 million years old and the towers are not
The register dates the formation to the Cretaceous Period, between 70 million and 75 million years ago. The hoodoos are only the shape that rock is passing through now. The register says they erode “quicker than virtually any other geological structure.” At one centimetre a year, a column three metres tall represents 300 years of erosion, by simple arithmetic. That is a rounding error against the age of the rock and a long time against a human lifetime.
A heritage designation cannot slow a centimetre a year
Alberta recognized the Hoodoos as a Provincial Historic Resource on January 25, 2001. Most designations protect something that was made and can be maintained. This one names a formation whose defining feature is loss, and no restoration can put back shale that has washed down the valley.
About 10 columns stand between Drumheller and East Coulee. By the register’s own rate, next summer will have taken another centimetre.
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