There are quite a few theories for the
development of the coulees we see today. In any case, it is known that
the coulees were originally formed by the final glaciation of the
Pleistocene, known as the Wisconsin glaciation. When the glaciers of
the Wisconsin retreated, large amounts of water flooded the
Saskatchewan landscape. These meltwaters forged the dry valleys that
lead into the Qu'Appelle River. These dry valleys are called coulees.
Geomorphologists have began to think the coulees we see today aren't
entirely the product of the Wisconsin glaciation.