 SR 503 intersects its spur route and turns west to parallel the Lewis River downstream to Woodland, where the highway ends at an interchange with Interstate 5 (I-5).The highway was part of the Lewis River Road, signed as State Road 15, from 1909 until 1919.The current route of SR 503 was split between Secondary State Highway 1S (SSH 1) from Woodland to Battle Ground and SSH 1U from Battle Ground to Orchards in 1937, combined to form SR 503 during the 1964 highway renumbering.