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The Parks / Northwest Territories / Nahanni National Park Reserve

Millions of years ago, the South Nahanni meandered its way along a flat sedimentary plain. When forces deep within the earth forced molten rock to the surface to form the Ragged Range, everything before it rippled, creating the Mackenzie Mountains, but the river held its course. So the river behaves like a mature meandering river, which has gradually worn its way through the rock while the mountains rose around it. For 80 kilometres, the South Nahanni travels through the largest canyon system in Canada, actually the largest in the world north of 60 degrees latitude.

The river began carving these canyons about 1.4 million years ago. Their existence today is an anomaly here. Glaciers covered so much of the North that most landforms tend to have been altered significantly as recently as the last glaciation 10,000 years ago. But this area escaped glaciation because the mountains to the west intercept most of the precipitation and there simply wasn't enough snow to build up a glacier. Hence the mountains and river canyons have not been widened or rounded by the crush of ice.