Hollowtop Mountain is the highpoint of Montana's Tobacco Root Mountains, named for the concave shape of its northeast face. The longest, most scenic standard route starts from the North Willow Creek trailhead near the town of Pony.
From the North Willow Creek trailhead near Pony, MT, a well-marked trail leads to Hollowtop Lake. From there the route leaves the trail and follows the banks of three lakes (Hollowtop, Deep, and Skytop) before a steep, off-trail scramble on loose rock to the summit.
Most parties reverse the ascent route; a shorter, steeper west-side approach via South Boulder River Road (about 3 miles one-way with roughly 3,700 feet of gain) and an east-side approach from Mason Lake are also used by some parties.