Local residents may remember a mid-June morning in 1990 when, after a severe rainstorm and resulting floods, 32 acres of farmland plunged into the Saddle River about 12 km northeast of Rycroft. The toe of the mass of earth powered into the riverbed and pushed 20 metres up the opposite bank. This quite effectively dammed the river.
It was the largest historic landslide in Alberta, and the first historic landslide dam on the Interior Plains.
There is much more information about this event in a paper from the University of Alberta. You’ll find maps and diagrams showing what exactly happened to trigger the slide.
Thanks Nonny Moose for the link!