Start at the Snow Lake Trail and follow it until its terminus at 1.3 miles (See main page for directions).
Follow the boot path to the right as far as it goes and then onto the boulder field. Aim for the evident gap in the ridge to the southeast and climb up a steep gulley containing a snowmelt stream.
At the top of the gulley, either proceed forward up the talus slopes to the furthest ridge, or, alternatively, climb the bootpath to the left to leave the rocks and proceed through a series of meadows and snowmelt ponds.
Once on the southernmost ridge, proceed to the right (west) and follow the ridge to the base of Foss Peak. Some fairly straightforward scrambling will get you to the top in about 10 minutes time.
Since the steep gulley leading to the valley that spans between Unicorn Peak and Mt. Foss is very prone to rockfall, a helmet, while not a necessity, is not a bad idea.
In winter an ice axe and crampons are necessary.
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