The North Fork of the Big Wood drainage is the hiking epicenter of the Boulder Mountains. The main canyon accesses two large tributaries, the West Fork of the North Fork (WFNF) and the East Fork of the North Fork (EFNF). The hikes ascend dramatic, steep-walled canyons, that access multiple alpine cirques ringed by the highest peaks in the range.
The underlying geology of the North Fork of the Big Wood River is a combination of sedimentary and volcanic rock. Neither is particularly durable, and both rock units tend to break apart. A wide variety of individual rock units provide a wash of reddish and brown hues that blend together in large, sweeping faces of talus and scree in the upper elevations. Below tree line much of the underlying rocks are covered with forests and soil, but the canyon walls are consistently steep down to the valley floor.
While not as dramatic as the West Fork, the trail up the North Fork of the Big Wood River offers a nice walk across open sage hillsides above the north side of the creek. A pretty waterfall cascades over a limestone ledge about halfway up the canyon. This trail accesses the West Pass Creek adventure.
Look for the trail leaving the east end of the parking lot. After climbing 200 feet through a shallow notch past an old mining prospect, the trail drops steeply to the creek to access an alternate route for horses. Hikers should continue along the east side of the canyon and climb across a steep, narrow side-hill above the creek. The trail then meanders across sage benches and through open Douglas fir forests for the first mile.
After a mossy creek crossing, the trail skirts the edge of a large alluvial fan accumulating beneath the west face of Ibex Peak. Observant hikers will notice a patch of wild raspberries that begins to bear fruit in mid-July. Continue through a short section of shady, aromatic forest before reaching a cairn/sign in an open meadow that marks the junction with the West Pass Trail
Enjoy another half mile of shade before emerging into a landscape of sagebrush slopes swept by frequent winter avalanches. A narrow limestone gorge comes into view at 2.5 miles, and hikers will enjoy the waterfall cascading out the bottom.
Beyond the waterfall, hikers are greeted with a sweeping panoramic view of the peaks at the head of the drainage. The trail continues its gradual climb beneath avalanche paths and across several springs between short fingers of forest before fading into the woods after 3.9 miles.
There are three main lobes at the head of the North Fork of the Big Wood that are ringed by a massive 10,000-foot to 11,000-foot ridge. Though much of the terrain above 9,500 feet is dominated by challenging talus and scree slopes, there are several routes worthy of exploration.
The northernmost lobe offers two great off-trail scrambles. The main access to Glassford Peak (11,602 feet) climbs to about 8,800 feet before trending northeast into a prominent 10,000-foot saddle above West Pass Creek. For a less committing peak scramble, continue up the left side of the northern lobe for before finding a way onto the south ridge of Ibex Peak (10,896 feet). This picturesque ridge is dominated by broken reddish rock with several prominent white dikes that cut horizontally across.
Ambitious hikers with good off-trail map skills might choose to navigate the western lobe through patchy forest to tree line. From here it is possible to climb to the divide with the West Fork of the North Fork and make a loop route through both canyons. Once at the divide, it is a relatively short scramble up the southeast ridge of Peak 11,298.
Reference: All content excerpted from Exploring Sun Valley - A Comprehensive Guide to the Boulder, Pioneer, and Smoky Mountains by Idaho River Publications.
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