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The Quaternary Period, encompassing the last two million years of geological time, is noteworthy for major climatic perturbations that resulted in episodic growth and decay of continental ice sheets in middle latitudes of the Northern Hemisphere. One such ice sheet and smaller independent satellite glaciers repeatedly enveloped most of the Canadian Cordillera with the exception of the northern Yukon and parts of the western District of Mackenzie.

Global cooling at the beginning of each glaciation led to the expansion of cirque and valley glaciers in the high mountains of western Canada. As climate deteriorated, glaciers advanced and coalesced to form piedmont complexes and mountain ice sheets. Eventually, glaciers from separate mountain ranges joined to cover most of British Columbia, southern Yukon, and parts of westernmost Alberta, Alaska, and the northwestern conterminous United States. During most Quaternary glaciations, the Cordilleran Ice Sheet was continuously nourished from source areas in high mountain ranges, and ice flow was controlled mainly by topography. However, at the climaxes of a few glaciations, ice in the interior of British Columbia became sufficently thick for one or more ice domes to develop with surface flow radially away from their centres.

Glaciations ended with rapid climatic amelioration. Deglaciation occurred by complex frontal retreat and by downwasting accompanied by widespread stagnation. In areas of moderate relief, uplands appeared through the ice sheet first, dividing it into a series of tongues that decayed in response to local conditions.

Glaciers existed in the Canadian Cordillera during late Tertiary and early

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