27 October 2014


Posted by Callan Bentley

Driving west from Calgary, your first evidence of entering the Canadian Rockies’ Front Ranges is the startling sheer cliff of Yamnuska, north of the Trans-Canada Highway:


Yamnuska’s shape is a function of differential weathering of the two rock units that make up the mountain: Cambrian Eldon Formation limestone, and Cretaceous shales of the Brazeau Formation. The Cambrian is the uppermost of the two, which is a violation of superposition, considering these are both sedimentary rocks that form on Earth’s surface. Hence, we invoke a major thrust fault here: the McConnell Thrust, named for a pioneering geologist in these mountains.



From this perspective, Yamnuska appears to be a klippe, like Chief Mountain in northern Montana, but it is not actually physically disconnected from the main mass of limestone to the west of it, so it’s not quite a klippe… yet. Give it another couple million years of erosion, and maybe we can make it happen.