The highway crosses the Columbia River on the Brewster Bridge, which originally opened in 1928 and was destroyed in 1967 before being re-built a decade later.

The highway turns northwest, following the Columbia River towards Chief Joseph State Park.

SR 173 continues west, forming the southern boundary of the Bridgeport Bar State Wildlife Recreation Area before crossing the Columbia River into Okanogan County on the Brewster Bridge.

The highway enters Brewster and becomes Bridge Street, traveling north over Swamp Creek to end at an intersection with US 97.

[15][16] No major revisions to the route of the highway have occurred since 1970,[17] however the state tried unsuccessfully to transfer ownership of SR 173 and the Brewster Bridge in 1986.