Wash. Rev. Code § 86.09.433
At the time set for said hearing the county legislative authority shall be present at the place designated in the notice and if it appears that due notice of the hearing has been given, shall proceed to hear such objections to the base map as shall be presented and shall hear all pertinent evidence that may be offered. The county legislative authority shall have authority to adjourn said hearings from time to time to study the record and evidence presented, to make such independent investigation as it shall deem necessary and to correct, modify, or confirm the things set out on said base map or any part thereof and to determine all questions concerning the matter and shall finally make an order confirming said map with such substitutions, changes, or corrections, if any, as may have been made thereon, which order shall be signed by the chair of the county legislative authority and attached to said map.
RCW 86.09.433