Cowlitzfisherman-
Further taxing my limited knowledge.

Without doing any research as I recall the first of the salmonid type fish show up in the fossil records maybe 50 million years ago. The first of the salmon/trout type was around maybe 10 million years ago. Likely evolving in the Arctic which at that time would of had a climate somewhat like todays pacific Northwest conditions. Folks believe that the first of the "modern" trout to colonize the NW was cutthroat, followed by the redbands and then todays rainbow/steelhead. As this region expereinced glaciation various populations came and went as their basins were alternately were buried and exposed by ice that at times may have miles thick. As recently as 12,000 years ago the area north of Southern Puget Sound was ice covered. As that ice age ended and the ice receded our streams were colonized from populations found to the South, interior of the upper Columbia and/or the Queen Charolate Islands north of Vancouver Island.

I may have some of the details incorrect as my memory is what it was once. However believe the above will give you a sense of how long these animals have been our streams.

Tight line
Smalma