Although SR 173 is implicitly a secondary state highway (remember, Washington State no longer has an explicit division between primary and secondary state highways), SR 173 used to be part of the main route between Brewster and the Coulee City area. The original SR 173 bridge across the Columbia River at Brewster was built in the 1920s. The SR 17 Columbia River bridge at Bridgeport was not built until around 1950, about the time that nearby Chief Joseph Dam was under construction. The original bridge at Brewster, a continuous thru truss, caught fire while undergoing maintenance in the late 1960s. The present SR 173 bridge utilizes some of the piers from the original bridge. SR 173, beginning at Jct SR 17 and ending at Jct US 97, is 11.86 miles long.
Before 1964, SR 173 had been the Brewster-Bridgeport branch of PSH 10.
Primary State Hwys Secondary State Hwys