I heard that, for a long time, the Skagit was actually below the Baker. Some sort of block there.

I would really like to see a good post-glacier changes in drainages. Here is what I have heard of, mostly from geologists.

S Fk Nooksack went down Friday Creek to the Samish.

Upper Skagit, Cascade, Sauk, Suiattle, Whitechuck all went to the Stilly.

White (and of course Cedar) were Duwamish Tribs.

White, previously, went down S Prairie.

Crescent Lake and Sutherland were one and flowed into the Elwha.

I know other small creek movements, but those were the biggies that I have heard of and am sure there were more.

I guess the biggest, from the perspective of genetics, evolution, and stock formation is that 15,000 ybp Puget Sound did not exist; it all flowed out the Chehalis. As the glaciers retreated , fish moved in but no PS stock is "older" than 15K years.