Starting at Maroon Lake TH (9,580-ft) follow the wide “West Maroon Trail” as it gradually climbs the aspen laden benches above Maroon Lake. Continue about two miles to Crater Lake where you will come to a junction in the trail. Take the “West Maroon Trail” and follow it another 1.5 miles to a place where the trail will cross West Maroon Creek. Continue another 2.64 miles and 1,937-ft to West Maroon Pass at 12,440-ft.
From West Maroon Pass, start an obvious ascent up Belleview’s long south ridge. The first objective is to attain UN 13,210-ft, which resides about half way up Belleview’s south ridge route. The initial .30 mile of ridge is class 3, requiring good route finding on loose rock. I would consider it, easy class 3 on semi-dangerous rock. This section of ridge is also loaded with rock towers that can be traversed by its easiest route. Soon the ridge widens and it becomes an easy class 2 stroll to the summit of UN 13,210.
From here, descend 100-ft to a saddle that separates UN 13,120 and Belleview Mountain. Make your way to Belleview’s east face via Belleview's continous south ridge on loose class 2 terrain. Attaining Belleview’s summit by a direct ascent up the south ridge proper is not possible, you must contour around to locate the east face. From here the rest of the climb is class 3 on loose rock, and I would consider this the crux of the climb. Locate a section of broken ledges that ascends the left side of the face back to the south ridge and on to the summit. The last 20-ft is a bit exposed and the loose rock makes this section challenging. Descend you ascent route.