The history of river routes in that area is fascinating. At one time, I think it was before the big mudflow, the White was flowing through the lower South Prairie Creek valley. May explain the rather wide valley and smallish creek now.

I have always wanted to work with a geologist to map what the post-glacial stream locations were. So many have moved/changed. For example, the whole Sauk, Suiattle, Cascade went down the Stilly until Glacier Peak fixed it. Plus, we have moved a lot of streams like the whole situation in this thread.

Might make some of the "the salmon have been here (in this stream) for a million years" arguments go away.