RCW 36.04.060

Clark county shall consist of the territory bounded as follows, to wit: Commencing at the Columbia river opposite the mouth of Lewis river; thence up Lewis river to the forks of said river; thence up the north fork of Lewis river to where said north fork of Lewis river intersects the range line between ranges four and five east; thence due south to the Columbia river; thence with the main channel of said river to the place of beginning.