SSH 1R was added to the state highway system in 1937. This highway began at Jct PSH 1 (US 99, now I-5) in Castle Rock and headed easterly via Toutle to the boundary of the Columbia (now Gifford Pinchot) National Forest NW of Mount St. Helens. 1961 legislation extended this highway into the national forest to Spirit lake then south closer to the mountain. This route became SR 504.
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