McCullough Gulch climbs a glacial valley on the north side of Quandary Peak. The popular route is about 2.9 miles round trip with roughly 600 feet of gain, ending at White Falls and the lower alpine lake at about 11,900 feet. Along the way you pass cascading waterfalls, granite slabs, and July wildflower displays; mountain goats are common on the upper slopes, so give them at least 50 yards. Remnants of late-1800s mining activity dot the upper Blue River valley around the trailhead.

There is no walk-up parking in summer (roughly June through September). Access is by paid parking reservation or shuttle only, booked at hikequandary.com: ride from the Breckenridge South Gondola parking structure to the Quandary Peak trailhead ($7 round trip for visitors, free for Summit County residents), then take the free connecting shuttle to McCullough Gulch, which runs 8am-4pm daily.

Snow lingers in the gulch into July. In winter, access is on foot and avalanche awareness is required.