Mount Formidable/South Route

This climb covers a section of the Ptarmigan Traverse. For those wishing to do a more committing intermediate-level glacier climb but don't necessarily have the time for a full-traverse (usually requiring a week) this is a great option. The climb can be done in two days with a long summit day, or as a more leisurely three day.

getting  there

Drive to Marblemount on SR-20. Register at the Marblemount Ranger Station. Take the Cascade River Road (Forest Road 15) for 22.3 miles to the Cascade Pass Trailhead, the large parking lot at road's end (3,600 ft).


Follow the Cascade Pass trail for 3.7 miles.  At the pass (5,400 ft), look for a climber's trail to climber's right, bearing SSE.  The climber's trail makes a rising traverse along snow or heather on the flanks of Mixup Peak's east slopes. Continue traversing until you reach the base base of the Cache Glacier (~6,000 ft), crossing a spur ridge en route.  Ascend moderate snow slopes to Cache Col (6,900 ft).  Cross the col and make a descending traverse SSE to Kool-Aid Lake and good camping (6,120 ft).


The climbing route is complex and involved.  Beginning at Kook-Aid Lake, head S.  The first terrain feature to aim for is the broad Red Ledge near Arts Knoll.  Cross the ledge and attain a spur.  Gradually descend across varied terrain (meadows, snow, talus, and small rock ribs), heading for the icefall on the Middle Cascade Glacier (6,200 ft).  At the glacier, ascend snow or talus until you are able to access the glacier above the icefall (~6,500 ft).  Ascend the glacier SSE to the Spider-Formidable col (7,320 ft).

Cross the col and descend south to 7,000 ft, then continue west aiming for a prominent notch in a spur ridge trending southwest (7,000').  Cross the notch and scramble down a narrow gully into the basin beneath Mount Formidable's south slopes.  From here make a rising traverse NW, scrambling across two gullies.  Scramble over a spur ridge to reach a third gully, and scramble up this gully, then onto rock and a small snowfield, and finally, onto rock (Class 3) and continue N to the summit (8,325 ft).


Descend climbing route. 


Seattle to Trailhead 3.5
Trailhead to Camp 5-6 3,300, -800
Camp to Summit 4-5 2,800, -600
Summit to Trailhead 9-10 1400, -6400


Standard glacier travel gear, ice axe and crampons.


  • In late season Cache Col can become moated out and difficult to cross.
  • In early season, the traverse along the side of Mixup can be snow covered with bad runout.
  • This climb can be combined with a climb of Mixup Peak or Magic as a three-day climb.
  • This climb is the start of the Ptarmigan Traverse.
  • Suitable Activities: Climbing
  • Climbing Category: Intermediate Alpine
  • Seasons: June, July, August, September
  • Weather: View weather forecast
  • Difficulty: Intermediate Mountaineering Climb
  • Length: 20.0 mi
  • Elevation Gain: 6,100 ft
  • 8,325 ft
  • Land Manager: North Cascades National Park
  • Parking Permit Required: None
  • Recommended Party Size: 4
  • Maximum Party Size: 6
  • Maximum Route/Place Capacity: 12
  • USGS Cascade Pass
  • Green Trails Cascade Pass No. 80
  • Trails Illustrated North Cascades National Park
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