District IV shall include that portion of Whatcom County lying south of the southern boundary of District III, and that portion of Skagit County north of a boundary established by the western terminus of State Highway 536 (Memorial Highway) continuing east on that road to its intersection with Freeway Drive in the city of Mount Vernon; then north approximately one mile on Freeway Drive to the intersection of State Highway 538 (College Way) then east to that point where College Way intersects State Highway 9, then north along State Highway 9 to the intersection of State Highway 20, and then in an easterly and northeasterly direction along Highway 20 to the Whatcom County border.