A state highway to be known as state route number 5, and designated as a Washington green highway, is established as follows:
Beginning at the Washington-Oregon boundary line on the interstate bridge over the Columbia river at Vancouver, thence northerly by way of Kelso, Chehalis, Centralia, Olympia, Tacoma, Seattle, Everett and Mt. Vernon, thence northwesterly to the east of Lake Samish, thence northeasterly and northerly by way of Bellingham to the international boundary line in the vicinity of Blaine in Whatcom county.