Wash. Rev. Code § 47.52.137
Following the conclusion of such hearing the authority shall adopt a plan with such modifications, if any, it deems proper and necessary. Its findings and order shall be in writing and copies thereof shall be served by United States mail upon all persons having entered a written appearance at such hearing, and in the case of a state limited access facility, the county commissioners of the county affected and the mayor of the city or town affected. The authority shall also cause a resume of such plan to be published once each week for two weeks in one or more newspapers of general circulation within such county, city or town beginning not less than ten days after the mailing of such findings and order. Such determination by the authority shall become final within thirty days after such mailing unless a review is taken as hereinafter provided. In case of an appeal, the order shall be final as to all parties not appealing.
RCW 47.52.137