Two different routes have been numbered SSH 8E at different times since 1937.
The earlier SSH 8E, added to the state highway system in 1937, began at Jct PSH 8 (US 97) between Maryhill and Goldendale and headed easterly to Paterson, then northerly, ending at Jct PSH 3 (US 410) in Prosser. In 1943, the US 97 to Paterson portion of SSH 8E was transferred to the Maryhill to Kennewick branch of PSH 8. In 1953, the Paterson to Prosser portion of SSH 8E was transferred to another branch of PSH 8. The SSH 8E designation went into disuse until 1961.
In 1961, a different highway became designated as SSH 8E with provisions. This newer route began at Jct PSH 8 (US 830) at Lyle and headed northeasterly, much of the way along the Klickitat River, ending at Jct PSH 8 (US 97) in Goldendale. The provisions were removed in 1965. When the state highway system was renumbered, this route became signed as SR 122.
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