The Cordilleran ice sheet, which covered British Columbia during the Late Wisconsinan Glaciation (25,000 to 10,000 years BP), was long thought to have extended all the way to the outer coastline, blanketing even the offshore islands and preventing any early human migration along the Pacific Northwest coast.
However, ancient plant and animal remains found on several offshore islands provide evidence that some areas of land on the outer coast remained unglaciated and habitable during the Ice Age. These ice-free areas are called refugia, and evidence for their existence has been found off the Pacific coast from Alaska to southern British Columbia.
Animal remains dating to about 17,500 years BP have been found in On Your Knees Cave on Prince of Wales Island, Alaska. Bears were living at K-1 Cave on Haida Gwaii by about 14,500 years BP, and salmon were present there by 12,000 years BP. At Port Eliza Cave on Vancouver Island, a diverse range of animal, fish and bird remains were found, dating to about 18,000 – 16,000 years BP.
Although there is no direct evidence for human occupation of these refugia during the mid-glacial period, it is clear that a chain of habitable environments existed along the Pacific Northwest Coast, and that these environments could have supported people as they made their way down the coast.