RCW 58.28.440: Platted lands declared dedicated to public use.

All streets, roads, lanes and alleys, public squares, cemeteries, parks, levees, school lots, and commons, surveyed, marked and platted, on the map of any townsite, as prescribed and directed by the provisions of this chapter, are hereby declared to be dedicated to public use, by the filing of such town plat in the office of the county auditor, and are inalienable, unless by special order of the board of commissioners of the county, so long as such town shall remain unincorporated; and if such town at any time thereafter becomes incorporated, the same becomes the property of such town or city, and must be under the care and subject to the control of the council or other municipal authority of such town or city.