The Harriman Trail is an 18-mile non-motorized gravel path that follows the Big Wood River up the valley from the Sawtooth National Recreation Area headquarters, about 8 miles north of Ketchum, to Galena Lodge near the top of the valley. The Blaine County Recreation District (BCRD) manages it year-round in partnership with the U.S. Forest Service, and the whole route sits inside the SNRA. The trail is named for W. Averell Harriman, the Union Pacific chairman who founded Sun Valley. Construction started in 1991 with a pledge from the Mary W. Harriman Foundation, and the full length was finished in July 2001.

The south end starts at the SNRA headquarters on North Fork Canyon Road, just off Highway 75. The headquarters has a large parking area and is staffed on weekdays in season, which makes it the easiest place to start. From there the path runs north along the river and the highway, and several spots along the way let you get on or off: the North Fork area by the headquarters, Baker Creek, the Easley area, Billy's Bridge, Prairie Creek a few miles below Galena, and Cathedral Pines. Galena Lodge marks the north end, with its own parking, food in season and a connection to the Galena trail system. With that many access points, most people ride or walk one section rather than the full length. A car shuttle between the two ends is the usual way to do the whole thing one way.

The grade is gentle. Heading north from the headquarters, the trail climbs roughly 1,200 feet over its length. That averages under one percent, with short pitches up to about 6 percent. Dirty Freehub rates it Easier and lists a full out-and-back at about 39 miles with around 2,300 feet of climbing. The surface is compacted gravel and dirt the whole way, so a mountain bike, gravel bike or hybrid all work. It makes a good first long ride for kids or anyone new to riding at altitude. The stretch closer to Galena has more rolling hills and rock formations than the flatter southern miles, and interpretive kiosks along the way cover the history and ecology of the upper valley.

In summer the trail is open to walkers, bikers and horseback riders, and BCRD asks bikers to yield to hikers and horses. There is no fee for summer use. BCRD does not post a separate summer dog rule for the Harriman, so keep dogs under control and clear of horses and bikes, and pack out waste. Sheep bands graze parts of the upper valley in late summer and fall, including around Baker Creek, and guard dogs may be with them. Give them room.

In winter BCRD grooms the Harriman as the spine of its North Valley Nordic system. That system also includes the North Fork and Durrance loops at the SNRA headquarters, Lake Creek, Billy's Bridge, Prairie Creek and the Galena trails. BCRD lists the groomed Harriman at about 32 km, point to point between the headquarters and Galena Lodge. You need a BCRD day or season Nordic pass to ski or snowshoe the Harriman and the rest of the North Valley trails, and kids 17 and under ski free. Dogs are allowed in winter only on the southern section from the SNRA headquarters to Cathedral Pines, and BCRD sells a dog pass for its dog-friendly trails. Keep dogs under voice and sight control or on a leash, and pack out their waste. BCRD posts daily grooming reports on its TraiLink page, and conditions change fast at this elevation, so check before you drive up.