Interesting map. The predominance of Clovis on the eastern side of North America suggests that it originated there and then spread to the rest of the continent.
I was shocked when I first learned about how many Clovis finds there were in the eastern half of the U.S. I just associated Clovis with the original New Mexico find and the western part of the country.
There is a theory that people could have crossed the Atlantic simply by hunting and living on the sea ice, much like Inuit have done in the past. They just gradually worked their way across the ocean, rather than a bunch of people jumping into boats and crossing over in one move.