The John Wayne Pioneer Trail east of the Columbia is an adventure in itself. 4" tires and a Surly Long Haul Trucker seem to work on the ballast. The services are few and far between. Just finding water can be an issue.

This chap did it and produced a very informative account. I'd do it with a fully equipped sag wagon and bike shop.

Arlington, over Cascade Pass and on to Spokane, then onto the Centennial Trail there sounds better. Then you connect to the North Idaho Centennial Trail, work over to the Trail of the Coeur d'Alenes and on to Montana. There are a number of good trails in the Spokane - Silver Valley area. The TCdA is a tourist attraction.

<http://www.traillink.com/trailsearch.aspx?city=spokane&state=WA>

26InchSlicks: Crossing Washington State On The John Wayne Pioneer Trail