Wash. Rev. Code § 9.46.285
This chapter constitutes the exclusive legislative authority for the licensing and regulation of any gambling activity and the state preempts such licensing and regulatory functions, except as to the powers and duties of any city, town, city-county, or county which are specifically set forth in this chapter. Any ordinance, resolution, or other legislative act by any city, town, city-county, or county relating to gambling in existence on September 27, 1973 shall be as of that date null and void and of no effect. Any such city, town, city-county, or county may thereafter enact only such local law as is consistent with the powers and duties expressly granted to and imposed upon it by chapter 9.46 RCW and which is not in conflict with that chapter or with the rules of the commission.
RCW 9.46.285