Refer to the "getting there" section on the main mountain page to get to the Siyeh Bend Trailhead. Take the only trail (Siyeh Bend cut-off trail) uphill for about 1 mile. At the junction with the Piegan Pass Trail, turn left, toward Piegan Pass. After about 1/2 mile, the forest will clear and you'll be treated to your first views of Going-to-the-Sun Mountain (henceforth, GTTS).
Leave the trail when convenient, heading east-north-east toward the obvious saddle between GTTS and Matahpi Peak. On the way to the pass you will encounter two cliff bands. The lowest band, made of limestone, can be skirted to the south. Find a class 3 route (not unique) through the higher band, made of diorite. Mark your route to assist the descent.
After passing the second cliff band, scramble over class 2/3 terrain, to the right side of the Matahpi/GTTS saddle. Traverse south, along the base of a cliff band along the main ridge. A use trail exists, and makes the travel over these loose, steep slopes much easier. Follow the use trail south, around an obvious "corner" in the cliff band. The use trail leads immediately to a prominent gully (I call this "Nasty Gully", but the guidebook author, J. Gordon Edwards, calls it the "Diagonal Chute").
GMS Climb Classification System
The Glacier Mountaineering Society (GMS) climb classification system "expands on the system published in the Climber's Guide to Glacier National Park by J. Gordon Edwards. It contains information on the overall rating of a climb, the degree of difficulty of the most difficult pitch, the round trip distance and the elevation gain." The GMS system is outlined here.
The Diagonal Chute Variation of GTTS's West Face route would receive a III (4) M M C rating. This translates roughly to "mostly class 3, with short sections of class 4. Medium distance/elevation gain. Couloir."
Acknowledgement: Fred Spicker.
Nasty Gully holds permanent snow in its upper reaches. It is narrow; never more than 30 feet wide, has a slope angle of around 40°, and gains approximately 800 feet. Climb Nasty Gully as conditions dictate. About 30 feet before reaching the top, look for cairns on the right wall of the gully. Exit Nasty Gully and scramble up class 3/4 rock up the right wall. After 100 feet of climbing, you'll be near the top of a false summit.
The true summit is 1/4 mile to the south of the false summit. Enjoy the exposure as you walk the summit ridge. The last 150 feet to the summit is class 3 or harder, depending on your exact route. The easiest route skirts west of the main ridge.
Rope not necessary for the rock climbing. Class 4 sections are short, not terribly exposed, and probably avoidable in most cases.
Depending on snow conditions/coverage in Nasty Gully, you may bring an ice axe and crampons. In the summer (after July in most years), the snowfield in the gully can be easily skirted. Still, the axe is useful for self-belay during ascent and descent of Nasty Gully's heinous scree.
Water is not plentiful on this route.
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