The highway continues north through the vineyards of the western Wahluke Slope and passes a roundabout at the west end of Mattawa. North of Mattawa, the bluffs of the Saddle Mountains cause the river and its valley to narrow, leaving SR 243 to run directly on the eastern bank as it traverses the Sentinel Gap. Near Beverly, the highway passes under the Beverly Railroad Bridge, which carries the Palouse to Cascades State Park Trail, and moves away from the river bank to serve Wanapum Village near the Wanapum Dam. SR 243 continues north across the hills overlooking the dam's reservoir, passing through several rock cuts near the Sand Hollow Recreation Area, and descends to an intersection with SR 26, where the highway terminates. The junction is located south of an interchange with Interstate 90 (I-90) at the east end of the Vantage Bridge, where SR 26 itself terminates.