When the current state highway numbering system was first posted in 1964, SR 30 started at Jct US 97 in Tonasket and headed east via Republic to Jct US 395 a few miles west of Kettle Falls.
In September 1972, the final section of SR 20, the North Cascades Highway, was completed. SR 20 originally ended at Jct US 97 near Okanogan. In 1973 SR 20 was extended east to Newport. The SR 30 designation was replaced by SR 20 as part of this extension.
Before 1964, SR 30 from Tonasket to Republic was part of PSH 4; from Republic to the present junction of SR 20 and SR 21 a few miles east of Republic, part of SSH 4A ; and the rest of the way to US 395, SSH 3P.
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