Wash. Rev. Code § 36.04.190
Kittitas county shall consist of the territory bounded as follows, to wit: Commencing at a point where the main channel of the Columbia river crosses the township line between township fourteen and fifteen north, range twenty-three east of the Willamette Meridian, and running thence west on said township line to the range line between ranges eighteen and nineteen east; thence north on said range line six miles, or to the township line between the townships fifteen and sixteen north; thence west on said township line to the range line between ranges seventeen and eighteen east; thence north to the township line between townships sixteen and seventeen north; thence west along said township line and a line prolonged due west to the Naches river; and thence northerly along the main channel of the Naches river to the summit of the Cascade mountains, or to the eastern boundary of King county; thence north along the eastern boundary of King county to the point where such boundary intersects the summit of the main divide between the waters flowing northerly and easterly into the Wenatchee and Columbia rivers and the water flowing southerly and westerly into the Yakima river; thence in a general southeasterly direction along the summit of such main divide between the waters flowing northerly and easterly into the Wenatchee and Columbia rivers and the waters flowing southerly and westerly into the Yakima river, following the course of the center of the summit of the watershed dividing such respective waters, to the fifth standard parallel north; thence east along the fifth standard parallel north to the middle of the main channel of the Columbia river; thence down the main channel of the Columbia to the place of beginning.
RCW 36.04.190