The question comes from vague recollections of descriptions of the ice fields extending all the way down to the current New York city area in the North America region. Also, some about the ice fields being massive enough to gouge out the great lakes basins.
You are correct about the ice fields. But folks were already in Alaska some 30,000 or so years ago, before the heaviest ice. Some areas of Alaska or "Beringia" were not covered with ice, so people survived. Then, near the end of the last ice age there opened up a corridor between Alaska and the continental US. This is what allowed the land migration to take place while there was still a lot of ice around elsewhere.
Starting about the same time folks headed down the coast in watercraft. They were a lot quicker, but that migration didn't get too far inland.
Most of my concept and/or understanding comes from Discovery type “science” programming, so please, don’t hesitate to laugh out loud where appropriate...
But, in regards to the reasoning for not moving inland much distance during the boat migration, I had seen a program that said that was due, probably, to the mega-fauna such as what they called the “God Bear”, the saber tooth cat, and the dire wolf. Is there anything to that? Or was it the usual over simplified “for tv” stuff that often gets put out?
Also, is there any real solid evidence to a land bridge migration? I would assume that the mammoth and such type critters being distributed on both sides of the water would indicate such a thing, but has anything been discovered that pegs it as a certainty?
And, for general comm purposes:
Sciencer = Bureaucrat. Science is a job that requires no boat rocking and never indulges in consensus bucking.
Sciencian = Fundamental worshiper of the image of science. No questions asked. Devotion to whomever dominates in the academic cult of personality.
Scientist = the people that make it work and all too often get passed over in credit and reward for Sciencers and Sciencians.
Other than that, I was just being my usual snarky self. I like science, just don’t have the head for it.