Late Tertiary changes in the general circulation of the atmosphere, regionally enhanced by uplift of the Wrangell - Saint Elias and Coast mountains, were sufficient to promote permafrost development in the western Arctic. Permafrost developed in Yukon Territory and adjacent Northwest Territories during early Pleistocene glacial periods, after continued tectonic activity led to further modification of regional climate, but degraded in the interglacials. Permafrost has been present in northern parts of the region since the Illinoian glaciation, but most ground ice in central Yukon formed in the Late Wisconsinan. The present interglacial is the only one with widespread evidence of permafrost, which is maintained in the valleys of central and southern Yukon by the Saint Elias Mountains blocking continental penetration of maritime air from the Gulf of Alaska. This reduces snow depth in winter, while cold-air drainage in the dissected terrain of the Yukon Plateaus enhances the near-surface inversion, leading to continental minimum temperatures. -from Author
Canadian Journal of Earth Sciences
Department of Geography and Environmental Studies

Burn, C. (1994). Permafrost, tectonics, and past and future regional climate change, Yukon and adjacent Northwest Territories. Canadian Journal of Earth Sciences, 31(1), 182–191. doi:10.1139/e94-015