Forbidden Peak Circumnavigation

A challenging, technical, multiday glacier ski tour in the North Cacsades. It's roughly 21 miles and 12,000 feet of elevation gain that can be linked with a ski descent of Eldorado Peak or other peaks on the Ice Cap Slam.

Getting There

Drive I-5 to just north of Mount Vernon, then east on SR-20 (North Cascades Highway) to Marblemount. In Marblemount, turn right onto Cascade River Road. Drive ~20 miles to a large parking area on the right (2,100 ft). If the road is driveable, continue ~2 miles to the Boston Basin Trailhead (3,200 ft). Sometimes the road is gated at Mile 18, the national park boundary.

Ski Route

Suggested Itinerary

Day 1: The road is often snowed in at or before the Eldorado Peak Trailhead. If it is, walk and ski the road to the Boston Basin Trailhead. Ascend through the trees to Boston Basin. Camp 1 is traditionally located near the base of Shark Fin Ridge.
Day 2: Boot up Sharkfin Couloir  which may involve scrambling on chossy rock. Descend the back side onto the Boston Glacier, rappelling if needed. Skin up to Forbidden Couloir to access the Forbidden Glacier, descend to Moraine Lake, and climb towards the Inspiration Glacier. Camp 2 is typically located below Eldorado Peak.
Day 3: Ski out following the standard Eldorado Peak approach, first climbing Eldorado Peak if desired.


  • Exact locations of camps and ski route vary based on snowpack and conditions.
  • Be prepared to ski around seracs and rappel portions of the route, as parts of the route can melt out even in April.
  • A 30 meter rope should be sufficient for rappels and glacier travel, but this will vary depending on conditions.
  • Consider extending your trip and climbing some peaks along the Ice Cap Slam.
  • As of Nov 2022, following the Inspiration Traverse out towards Thunder Creek is not recommended, because of the bridge washout and required car shuttle.
  • Difficulty: Intermediate Mountaineering Climb, M3G Expert Glacier Ski
  • Length: 21.0 mi
  • Elevation Gain: 21,000 ft
  • Land Manager: North Cascades National Park
  • Parking Permit Required: None
  • Recommended Party Size: 6
  • Maximum Party Size: 12
  • Maximum Route/Place Capacity: 12
  • Green Trails North Cascades Ross Lake No. 16SX
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