This is a strike-slip fault, where part of Siletzia has been split off; the missing piece may be the Yakutat terrane now at the head of the Gulf of Alaska.
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Measurements of such paleomagnetic fields in the Oregon Coast Range show rotations of 46 to 75°, all of it following the presumed accretion to the continent (alternately, formation) of the Siletz terrane at about 50 Ma.
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Similarly, certain schists on Baranof Island are believed to have been contiguous with the Leech River Schists on Vancouver Island around 50 Ma, and subsequently transported northward with other elements of the Chugach-Prince William terrane.
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This can be resolved by assuming that by about 56 Ma the eastern part of the Kula plate had broken away to form the Resurrection plate, with the new Kula-Resurrection (K-R) spreading ridge running up the Gulf of Alaska towards Kodiak Island, and the former K-F (now R-F) ridge reaching Washington.