Some of the North-South valleys in the Yukon were left unglaciated. That's why they weren't scrubbed clean of their placer gold (and Mammoth ivory, if you've ever been there).
http://www.researchgate.net/figure/...imited-exploration-due-to-poor_fig4_237824212
They were expressways for FN migrants. The Bering land bridge is under water, now and was it glavciated? How can you tell?
First Americans Lived on Bering Land Bridge for Thousands of Years
Genetic evidence supports a theory that ancestors of Native Americans lived for 15,000 years on the Bering Land Bridge between Asia and North America until the last ice age ended
https://www.scientificamerican.com/...on-bering-land-bridge-for-thousands-of-years/
The simpler sea going natives sailed down the coast from there.
Any more questions?
While the ojibway legends talk about how they came from the east when the water levels were down and there IS NO LAND BRIDGE ON THAT SIDE. They crossed on the water edge of the ice cap where the sea going food was.