SSH 9A was added to the state highway system in 1937. This route began at Jct PSH 9 (US 101) in Port Angeles and headed westerly via Joyce and Pysht, then southerly, ending at Jct PSH 9 (US 101) at Sappho. In 1955, the north-south portion of SSH 9A was dropped from the state highway system and a northwestern extension via Clallam Bay to Neah Bay was added.
When the current state highway numbering system was first posted in January 1964, SSH 9A became signed as SR 112. In 1967, the legal description of the eastern terminus of SSH 9A/SR 112 was changed to read "in or near" Port Angeles. A new Elwah River Bridge was built as part of SSH 9A/SR 112 in the late 1960s and the junction with US 101 was moved to the western outskirts of Port Angeles.
The north-south section of SSH 9A that was dropped from the state highway system in 1955 was added back to the state highway system effective April 1, 1992 as SR 113
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