Drive State Route 20 east from Interstate 5 at Burlington. Turn left on the Baker Lake-Grandy Lake road and drive 23 miles to just opposite Shannon Creek Campground. Turn left on road No. 1152 and drive 4.5 miles. Turn right on road (1152)014 and drive another 1.4 miles to the end of the road, 2,500 ft (762 m). Hike the trail on an old logging road bed to the end in a brush-covered clearcut. Hike the trail steeply up onto Shannon Ridge above into the virgin forest. Follow this trail in forest to the open ridge with views of Mt. Baker. Then hike the ridge to its end below a pass that leads onto the southern flank of Mt. Shuksan.
From the pass "contour NNE on a talus [or snow] shelf between two cliff bands (keep close to base of upper cliff). Beyond the cliff the slope broadens and fans to the low-gradient terminus of Sulphide Glacier. Campsites before glacier; 3-4 hours (route has been cairned). Ascend the [glacier] which steepens at about 6400 ft. Above this rise, skirt crevasses on the left, as necessary, then aim toward the summit pyramid." From where the Hells Highway route achieves the Sulphide Glacier, just to the right of a rock pinnacle at about 7600 ft+, "travel NE across the firn to near its highest point at the center of the summit rock pyramid, which is 600 ft. high here...Here are a series of steep parallel rock gullies which lead to the summit (class 3)...the more central [gully] is standard. Note: Beware of party-inflicted rockfall; the summit slabs dip downward and are precarious when wet." Excerpted from "Cascade Alpine Guide : Climbing and High Routes : Rainy Pass to Fraser River" by Fred Beckey.
This route is ideal for spring ski climbs. Ice axe and climbing rope are a must. Bring a helmet and crampons for the summit couloir. Bring walking poles, which can be used with skis and are most helpful for the long walk.