This is an alternative route up Feather Peak, from a very remote location, Feather Pass (12360'+). Intricate and confusing routefinding, uncertain scrambling, and dead ends are key features of this route. Isolation is guaranteed. Rock quality is decent, but still somewhat questionable. Rewards are limitless.
You need to find your way to Feather Pass. This is a point, southwest of Feather Peak. It is a saddle between Feather and unnamed Pk 12840'+. This pass divides the Bear Creek drainage from the smaller drainage containing Merriam Lake, which drains into French Canyon and Piute Creek.
You could either start way way way out on the west side, and head up Bear Creek from Mono Hot Springs. Or you could start at Piute Pass, go over and head down Piute Creek, up French Canyon, up a side-drainage to Merriam Lake, and then North from there towards the pass. Or you can reach it from Royce Lakes, via Merriam Col (Class 2, between Merriam and Royce Peaks) or the Feather/Royce Saddle (Class 2+, up to 60 degree snow).
Secor describes a David Brower first ascent, "keeping to the south side of the ridge to keep difficulties to 3rd Class."
A better way to describe the route would be to say to cross numerous ribs and gullies along the length of the southwestern face, staying 300' or more below the ridge.
Starting from Feather Pass, head up toward the huge pinnacles on the SW Ridge. As soon as things get steep approaching the first pinnacle, start traversing out along a rib. Cross this rib, cross a gully. Cross another rib, cross another gully. Continue to pick your way along the length of the SW Face, staying about 100-300' below the ridgeline. There are times when it is advantageous to go up. Try not to go too low, or you will find yourself hopelessly far away from the summit.
Toward the top, you will come to the crest of a rib, and see no easy descent into the gully below it. At this point, head up the rib to the ridgeline, where you should see some fairly easy (Class 3) slabs along the ridge. Take these, and follow the ridgeline (with some more small diversions to the south) for another several hundred feet to the summit.
Secor (presumably via Brower) rates this climb Class 3. I found no chance of keeping it at Class 3. The very exploratory nature of this climb, with various options that may or may not work out, and numerous steep cliffs along the ribs, keeps the climbing at Class 4 for much of the time. Exposure is never too terrible, though, and the rock for the most part is relatively solid.
Descent is easy via the Southwest Chute.