The glacial history of Yukon Territory is unique in Canada. The rest of Canada was almost entirely covered by glacial ice during the last ice age (Late Wisconsin - 25,000 to 10,000 years B.P.), but much of the Yukon was free of ice. The region extending from the central and northern Yukon across Alaska and westward to northern Asia was a vast ice-free wilderness across which herds of now extinct grazing mammals and their predators roamed. Horses, camels, lions, mammoths, to name a few, survived in this ice-free area more correctly called a refugium. The Bering Sea did not exist at that time because sea level was more than 100 m lower than that of today. This lower sea level was caused by the fact that great quantities of water were tied up on the land as continental ice sheets. This ecological ice free region is called Beringia after the now submerged Bering land bridge between Asia and North America. The first people to enter the Americas entered through Beringia.