Cypress Hills (Canada) - Geology

Geology

The hills are not true mountains but are rather the remnants of erosion of a Tertiary plateau of sediment formed during the initial uplift of the Rocky Mountains. This uplift caused the plain above which the hills now rise to be elevated, with the result that rivers flowing to the north and south eroded most of the softer sediments onto the lower part of the Great Plains. Today, the Cypress Hills form a major drainage divide separating rivers draining to the Gulf of Mexico (via the Missouri River) from those draining to Hudson Bay and James Bay via the Nelson River; thus the Cypress Hills form a water divide. There is a ranch northwest of Eastend, Saskatchewan, called Dividing Springs Ranch; the water from this spring goes both south to Gulf of Mexico and north to Hudson Bay.

Because they formed a suture zone between the Laurentide and Cordilleran ice sheets, the Cypress Hills are the northernmost point in North America that remained south of the continental ice sheets during the Wisconsin glaciation. In fact, along with northern Yukon, Banks Island, some nunataks (e.g. on the Gaspé Peninsula and western Newfoundland) and possibly the Brooks Peninsula, the hills and their southern slopes are the only unglaciated land in present-day Canada. This gives them an appearance very different from the typical "alpine" mountains of most of Canada, with a flat top and steep sides. This suggests that during a very severe glaciation of the Pre-Illinoian Stage the hills would have become a true nunatak, like the serpentinite hills of Gros Morne National Park, Newfoundland.

The undulating terrain comes from a series of morainal ridges composed of glacial till deposited when a glacier paused during its retreat 15,000 years ago.