RCW 47.32.020

Whenever the department determines that the right-of-way of any state highway or any portion of the right-of-way of any state highway shall be made free from any and all obstructions, encroachments, and occupancy it shall forthwith cause to be posted, by a competent person eighteen years of age or over upon any and all structures, buildings, improvements, and other means of occupancy of the state highway or portion thereof, other than property of public or quasi-public utilities, by virtue of a valid franchise, a notice bearing a copy of the order and dated as of the date of posting, to all whom it may concern to vacate the right-of-way and to remove all property from the right-of-way within ten days after the posting of the notice, exclusive of the date of posting. The department shall also require the filing of duplicate affidavits in proof of the postings, showing upon what structures, buildings, improvements, or other means of occupancy of the state highway or portions thereof, respectively, copies of the notice were posted and the date of each such posting, sworn to by the person making the posting.