Washington Constitution Art. 24, § 1. State Boundaries

The boundaries of the state of Washington shall be as follows: Beginning at a point in the Pacific ocean one marine league due west of and opposite the middle of the mouth of the north ship channel of the Columbia river thence running easterly to and up the middle channel of said river and where it is divided by islands up the middle of the widest channel thereof to where the forty-sixth parallel of north latitude crosses said river near the mouth of the Walla Walla river; thence east on said forty-sixth parallel of latitude to the middle of the main channel of Shoshone or Snake river, thence follow down the middle of the main channel of Snake river to a point opposite the mouth of the Kooskooskia or Clear Water river, thence due north to the forty-ninth parallel of north latitude, thence west along said forty-ninth parallel of north latitude to the middle of the channel which separates Vancouver's island from the continent, that is to say to a point in longitude 123 degrees, 19 minutes and 15 seconds west, thence following the boundary line between the United States and British possessions through the channel which separates Vancouver's island from the continent to the termination of the boundary line between the United States and British possessions at a point in the Pacific ocean equidistant between Bonnilla point on Vancouver's island and Tatoosh island light house, thence running in a southerly course and parallel with the coast line, keeping one marine league off shore to place of beginning; until such boundaries are modified by appropriate interstate compacts duly approved by the Congress of the United States.