The Mount Aix/Nelson Ridge Lollipop Route was designed by two-time UPWC BadAss Of The Year "Jaunty" John T. Barrickman. Here is John's description of the route:
Low point = 3,678’
High point = 7,474’
Cumulative E gain = 9,655’
Distance = 26 miles
Green Trails Map = 303S Goat Rocks/William O Douglas Wilderness
“The Mount Aix trail leads to a lofty world above the tree line, with views in all directions, and access to other trails for wandering in the open. On a clear day, you can see Mount Adams, Mount St. Helens, the Goat Rocks, Mount Rainier, and the Stuart Range, just to mention the more identifiable peaks.
The trail starts out at 3700 feet on a dusty path leading through moderately thick forest. At 0.3 mile is an easy stream crossing.
At 0.4 mile, the trail traverses to the south, at first level, and then gaining ever more in steepness until beginning a series of switchbacks a half mile later. The switchbacks and traversing combine to take you through a steep-sloped forest, featuring numerous and diverse varieties of trees. At 2.5 miles the canopy begins to thin, and the shade lessens. Finally, one last long traverse takes you up to an exposed ridge at 7150 feet, 4.4 miles. A weathered sign at a junction identifies the Nelson Ridge Trail #984 to the left. To the right and up continues the Mt. Aix Trail #982. Both of these trails connect to a third, the Richmond Mine Trail #973, as part of a 17-mile loop that stays above 4400 feet. The loop gets little use however, and may require routefinding skills.” - WTA
The official route would start at the Mt Aix TH, tag Mt Aix and continue east on the Mt Aix trail (982) dropping down to Dog Creek. At Dog Creek, turn N NW on the Richmond Mine Trail (973) until the North Fork of Rattlesnake Creek. Just past NFRC I would turn westerly on the Nelson Ridge Trail (984) and circle back to the intersection with Mt Aix trail. Another 4.5 miles back down would put me back at the car completing the route.
Map and GPS track available here: https://caltopo.com/m/CFDS
The route is described in detail by The Jaunty One himself in the following video, beginning at the 33:05 mark: https://youtu.be/EySlihW4l4E
John's trip report for the route can be read here: https://www.wta.org/go-hiking/trip-reports/trip_report.2019-09-08.4732031142