Wash. Rev. Code § 81.36.090
Any railroad corporation chartered by or organized under the laws of the United States, or of any state or territory, whose constructed railroad shall reach or intersect the boundary line of this state at any point, may extend its railroad into this state from any such point or points to any place or places within the state, and may build branches from any point on such extension. Before making such extension or building any such branch road, such corporation shall, by resolution of its directors or trustees, to be entered in the record of its proceedings, designate the route of such proposed extension or branch by indicating the place from and to which such extension or branch is to be constructed, and the estimated length of such extension or branch, and the name of each county in this state through or into which it is constructed or intended to be constructed, and file a copy of such record, certified by the president and secretary, in the office of the secretary of state, who shall endorse thereon the date of filing thereof, and record the same. Thereupon such corporation shall have all the rights and privileges to make such extension or build such branch and receive such aid thereto as it would have had had it been authorized so to do by articles of incorporation duly filed in accordance with the laws of this state.
RCW 81.36.090