This is a 7.4 mile loop with tremendous views of the Columbia River Gorge. A section of the trail is closed during Peregrine Falcon nesting season, so if you want to walk the full loop do not visit between February 1 and July 15. This trail can be rough and steep in places.
In addition to the loop trail, there are other connecting trails the can be explored. For example, a short distance west of Pioneer Point the trail follows the power line road. Turn north-east on the power line road, and you could follow it through to Canyon Creek Road.
Cape Horn Loop Trail 
Pioneer Point on Cape Horn Loop Trail 
Pioneer Point on Cape Horn Loop Trail 
Cape Horn Loop Trail 
Wahkeena Falls across the Columbia River 
Cape Horn Loop Trail 
Cape Horn Loop Trail map 
Cape Horn Loop Trail
Pioneer Point on Cape Horn Loop Trail 
Cape Horn Loop Trail
The easiest location to start on the trail is the Salmon Falls Park and Ride at Salmon Falls Rd and Highway 14. The Upper Trailhead would make for an easier walk to the high viewpoints. Parking on Cape Horn Road is less desirable, but could allow for more easily exploring the lower section of the trail when it is not Falcon nesting season.
