When the current state highway numbering system was first posted in January 1964, US 10 functioned as SR 10. US 10 started in Seattle at Jct US 99 and headed east via Snoqualmie Pass and Spokane, crossing into Idaho about 300 miles east of Seattle. I-90 has replaced US 10 as the most important east-west route across the state. US 10 was decertified as a US highway from Seattle to Spokane in 19690 and from Spokane to Coeur d'Alene Idaho in 1975.
State Route 10, part of former US 10, starts at Jct SR 970 at Teanaway near Cle Elum and heads ESE along the north side of the Yakima River to Jct US 97 near Ellensburg. The mileposts on SR 10 are based on those from old US 10 originating in Seattle. SR 10 is 16.16 miles long.
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