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  • The Cordilleran ice sheet was a major ice sheet that periodically covered large parts of North America during glacial periods over the last ~2.6 million years. This included the following areas: Western Montana The Idaho Panhandle Northern Washington state down to about Olympia and Spokane, Washington All of British Columbia The southwestern third or so of Yukon Territory All of the Alaska Panhandle South Central Alaska The Alaska Peninsula Almost all of the continental shelf north of the Strait of Juan de Fuca The ice sheet covered up to two and a half million square kilometres at the Last Glacial Maximum and probably more than that in some previous periods, when it may have extended into the northeast extremity of Oregon and the Salmon River Mountains in Idaho. It is probable, though, that its northern margin also migrated south due to the influence of starvation caused by very low levels of precipitation. At its eastern end the Cordilleran ice sheet merged with the Laurentide ice sheet at the Continental Divide, forming an area of ice that contained one and a half times as much water as the Antarctic ice sheet does today. At its western end it is believed nowadays that several small glacial refugia existed during the last glacial maximum below present sea level in the now-submerged Hecate Strait and on the Brooks Peninsula in northern Vancouver Island. However, evidence of ice-free refugia above present sea level north of the Olympic Peninsula has been refuted by genetic and geological studies since the middle 1990s. The ice sheet faded north of the Alaska Range because the climate was too dry to form glaciers.

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