From the Green Mountain Trailhead follow the Green Mountain Trail for approximately 0.6 miles until you see a marsh on the south side of the trail. The coordinates of this point are 40.310133°N / 105.831783°W. Cross the marsh and head up Green Mountain's forested northwest slope to the summit of Green Mountain.
From the summit of Green Mountain, descend Green Mountain's southeast slope to the Tonahutu Creek Trail at an elevation of 9320 feet and a point where you can cross Tonahutu Creek. There is a fallen tree here which allows passage across the river. The coordinates of this point are 40.291583°N / 105.813133°W. In "RMNP The Complete Guide" by Lisa Foster, the author recommends crossing the creek at an elevation of 9200 feet (0.2 miles farther south). In late June of 2009 I inspected that area for safe passage across the river, but the water level was too high and the river too narrow and deep to cross the raging Tonahutu at that point. That is why I recommend crossing at the coordinates which I provided.
After crossing Tonahutu Creek, gain 1400+ vertical feet as you hike one mile up Nisa Mountain's northwest ridge to its summit.
From Nisa Mountain's summit, head east for 0.3 miles to the saddle between Nisa Mountain and Mount Patterson, then hike for an additional 0.9 miles gaining 800 vertical feet as you head up Mount Patterson's southwest slope to the summit of Mount Patterson.
From the summit of Mount Patterson, descend Mount Patterson's northwest ridge to a saddle between it and Point 11,008, then climb to the top of Point 11,008. Descend Point 11,008 to the west, eventually arriving at Big Meadows. Less than 0.1 miles south of where the Green Mountain Trail meets the Tonahutu Creek Trail there is a bridge which crosses Tonahutu Creek. Cross the bridge to get to the Tonahutu Creek Trail, head north for 0.1 miles to the Green Mountain Trail, then take the Green Mountain Trail west for 1.8 miles back to the trailhead.