10 of us (in 2 cars) did this long loop of about 16 miles, 3600' gain - most of which is at the end, which is taxing. I don't recommend this loop. 
The High Prairie trailhead, however, is lovely. At almost 6000', a bit chilly. The meadows next to the trailhead was filled with shooting stars. This is the best shooting star display I've ever seen. You can also see a bit of Mt. St Helens here. So I recommend coming up via Hwy-35 (to have your workout, and an easier and shorter driving - see my last trip to Lookout Mt), make the detour of 2.9 miles for the loop to High Prairie.
The first ~1 mile of this hike is gentle going up, to this pointed rock, and then leveled along a rocky cliff with excellent views, until Lookout Mt summit (~6525'), where you can see Hood, St. Helens, Rainier, and Adams. Jefferson is a bit faint. All is glorious.
From Lookout Mt, we took the Lookout Mt Trail east, slowly loosing elevation to Oval Lake (not worth the 1/4 mile detour to the lake -- going down, and it's shallow and ugly). 
The trail is more or less along a ridge. View is not bad for the first mile before going into the woods. Still had snow left. 
20 minutes past Oval Lake, we slowly regain the ridge, and view. Saw big patches of Jacob's Ladder (and some white ones), Wild Candytuft (Noccaea fendleri), Paleyellow Ragwort. Then we hit a road. Walk in-and-out on the rocky road to the Flag Point Lookout tower (the tower is in the middle right, furthest in the photo). 
It was closed. But the compost bathroom was open: clean and spacious. Had lunch next to the tower. I sat under the tower, great view, but windy. The rest of the group sat in the trees without wind or view. Some Oregon anemone here.
After the lookout tower, we headed down to Badger Creek, and back up along Gumjuwac Creek. This part is unpleasant: mud patches, very overgrown (Badger Creek wilderness). Met no human. Found 3 large king boletes in the same spot, all in good shape: strange. Woodland flowers. Large ponderosa pines. Saw rusted vine maple leaves and tainted lupine leaves. Orange honeysuckle! We reached out lowest elevation at ~3000' after about 8 miles, when we turned on Badger Creek trail, which is mostly flat. Then, we turned right onto Gumjuwac Creek trail, gaining the elevation back.As we approach Gumjuwac Saddle (~5200'), started to emerge in and out of forest. View got better, and it's dryer. Saw mariposa lily, gilia, blooming balsamroot. Back to the junction of High Prairie trail, and hike down back to car. We are back at the trailhead at 6pm. Then, I got a ride home.
