Washington Revised Code Title 36. Counties § 36.04.400. Survey of county boundaries

All common boundaries and common corners of counties not adequately marked by natural objects or lines, or by surveys lawfully made, must be definitely established by surveys jointly made by all the counties affected thereby, and approved by the board of county commissioners of such counties. The cost of making such surveys shall be apportioned equally among the counties interested, and the board of county commissioners shall audit the same, and the amounts shall be paid out of the county current expense fund.