They either arrived before the LGM or during it. I think that we will eventually find evidence that they arrived in North America during a period of climate transition just before the LGM was complete.

As glaciers were forming and growing, more land was exposed creating islands in what later became Beringia. A marine culture in Asia could have island hopped to the Pacific Coast of N. America before glaciers had reached that far. Once on the N. American Pacific coast, they would have followed streams and rivers inland.

No doggy prints.