Wash. Rev. Code § 36.04.120
Garfield county shall consist of the territory bounded as follows, to wit: Commencing at a point in the midchannel of Snake river on range line between ranges thirty-nine and forty east, W.M.; thence on said line south to the southwest corner of township twelve north, range forty; thence east on township line six miles; thence south to the southwest corner of section seven, township eleven north, range forty-one east; thence east one mile; thence south three miles; thence east one mile; thence south one mile; thence east one mile; thence south three miles; thence east three miles; thence south on township line to the Oregon line; thence due east on said line six miles to the southwest corner of Asotin county; thence northerly following the westerly boundary of Asotin county to a point where the same intersects the midchannel of Snake river; thence down the said midchannel of Snake river to the point of beginning.
RCW 36.04.120