Washington East on 20 or West on 20 -- US2

Much of 20 is Nat Park or Rec area, which prohibits camping outside of established campgrounds. The Forest Service allows dispersed camping, but in heavy forest suitable sites can be hard to find. At the peak of the summer knowledgeable locals will have claimed the best ones. Others are too rough, too far off the main highway, or trashed. It's easier to find dispersed sites on the east side of the mountains. West side FS campgrounds are nearly all concessionaire operated, and on the reserve system. The NP is putting more of their sites on reserve.

Good hiking close to the highway is more abundant along 20, ranging from short paved trails to the Pacific Crest. Most of the US2 trailheads are someways off on FS roads.