SR 26 begins at an interchange with I-90 on the east end of the Vantage Bridge on the Columbia River, opposite the town of Vantage and the Ginkgo/Wanapum State Park. The highway travels south for to the mouth of the Sand Hollow, where it intersects SR 243, which continues downriver to Mattawa and the Vernita Bridge. SR 26 turns southeast and travels up the barren Sand Hollow to the Royal Slope and its irrigated fields, situated between the Frenchman Hills to the north and the Saddle Mountains to the south. The highway continues east across the plateau's farms and turns southeast at Royal City, near which it intersects SR 262. SR 26 crosses into the Columbia National Wildlife Refuge in the foothills of the Saddle Mountains and enters Adams County near Tauhton.