 SR 503 was established during the 1964 highway renumbering and codified in 1970 as the successor to SSH 1U and part of SSH 1S between Battle Ground and Woodland, while the remaining portion of SSH 1S between Mount Vista and Battle Ground became SR 502. The highway in the Lewis River valley, between Woodland and the Yale Bridge, was closed following the May 18, 1980 eruption of Mount St. Helens and re-opened after the Yale Bridge was placed on the National Register of Historic Places in July 1982. The spur route of SR 503 was added to the state highway system in 1991 as part of the original Lewis River Road between Yale and the Skamania county line in the Gifford Pinchot National Forest. Between Orchards and Amboy, SR 503 was designated as the "Lewisville Highway", serving historic Lewisville Park.
