That's a heck of a lot of territory to be covering. Since I just moved up here and don't have a lot of experience I will try my best being an Oregon native.
My Dad said that the Deschutes is on fire right now, so if you head out towards Bend then hit the Deschutes, or even Fall River outside Sunriver. If you want to stay west of the mountains hit the Salmon or Sandy rivers outside of Welches and Sandy, respectively, on HWY 26.
I hope that this helps a little, but there is a ton of water to hit between Seattle and Bend.
I don't think my first post was very clear. I'm looking for some good trout rivers within 1 hour of Portland and Yakima. There's probably too much to mention, but we're both fairly experienced flyfishers and would like to catch some bigger fish.
Unfortunately there is only one good Trout river with bigger fish within an hour of Yakima, and you named it. There are a few smaller streams with some nice smaller fish. (just check a map) Can't help you with Portland for trout, although; the Kalama is a nice river for Silvers or steelhead.
I fish the Kalama River which is off of Kalama River Rd on I-5. Follow the road east and you will find many turnouts to which you will find great water. Right now is fly fishing only on some of the most productive salmon/steely water. You can fish downstream of the Fish hatchery pump house to the pipeline with flies only, until Oct 31st. Salmon and steelies run rampant thru hear this time of year. There is a great possibility of hooking both. I have had excellent luck with steelhead if your fly is presented to their level...they are not chasing flies...Best of luck! :YUM
It may be a little more than an hour but drive to Maupin and fish the Deschutes. I have a buddy who lives in Bend and drives up to Maupin just about every weekend and he said it is getting crazy. The 6-7 times that I have been out there this year have been successful. There is excellent water. Good Luck.