27 October 2014
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.