North of West Bush, the route rapidly ascends in elevation as it climbs up the side of a large mountain. Along this stretch, the route veers to the northwest and southeast as it heads through an area of wilderness. NY 309 crosses the Blue Line into Adirondack Park near the mountain's summit. Upon reaching the top of the mountain, the highway straightens out and heads northward for roughly across the hill's plateau. Upon reaching the other side, the road gradually descends in elevation as it passes by Mountain Lake and enters the town of Bleecker. The highway continues its northeastward descent into the small lakeside hamlet of Bleecker, where NY 309 ends at an intersection with Lily Lake Road. At this point, the roadway becomes CR 112.