To help you visualize the route, courtesy of Erin (“Wired”) Saver.
Note: This video portrays the original Primary Route, which I changed after my July 2015 thru-hike. In particular:
1. From Dumbbell the Pass the Primary Route now goes over Amphitheater Pass and descends Cataract Creek to the JMT in Palisades Creek; the route over Observation Peak Pass and Adventurer Col remains an alternate, but it is unnecessarily hard.
2. From Black Giant Pass the Primary Route now climbs through Ionian Basin into upper Goddard Creek, which it descends all the way to the Middle Fork at Simpson Meadow. The route down Enchanted Gorge remains an alternate, but it’s the inferior route — it offers less time in Ionian Basin, and it is a less pleasant descent.