Wash. Rev. Code § 89.30.619
If the annual assessment roll or segregation thereof for any general improvement or divisional district authorized under this chapter, has not been delivered to the respective county treasurers concerned on or before the first day of January following the equalization thereof, any said county treasurer shall immediately notify the secretary of the district by registered mail that unless said roll is delivered to said county treasurer within ten days from the receipt of said notice, the board of county commissioners of the county in which the organization of the reclamation district was effected will cause an assessment roll for the district to be prepared and shall equalize the same if necessary and make the levy required by this chapter.
RCW 89.30.619