Washington Hwy. 129 - Oregon Hwy 3

I have taken our small trailer via that route. Fields Spring State Park at the top of the Rattlesnake Grade just on the WA side is a nice stop or layover. The Rattlesnake Grade bear the state line is scenic and historical, but its steepness and sharp curves are true to the name. Here is a blog (not mine) that describes the route well:
http://destinations-northwest.blogspot.com/2012/04/rattlesnake-grade-road-to-remember.html?m=1