 SSH 1S was created in 1937 during the formation of the primary and secondary state highways, traveling on a route east from Primary State Highway 1 (PSH 1) and U.S. Route 99 (US 99) north of Mount Vista to intersect SSH 1U in Battle Ground and turned north towards Amboy and west to end at PSH 1 and US 99 in Woodland.After PSH 1 and US 99 was realigned onto a four-lane limited-access highway in the late 1940s, SSH 1S was extended south over the old highway to intersect PSH 1 and US 99.SR 502 was established during the 1964 highway renumbering and codified in 1970 as the successor to the Mount Vista–Battle Ground section of SSH 1S, while US 99 was replaced by I-5.