This route is named for the Mt. Whitney Portal Store's Doug Thompson, who described it to me. It is an interesting alternative to New Army Pass and Army Pass, the routes most commonly used by hikers seeking the summit of Mt. Langley. The route involves cross-country travel, but never exceeds Class 2. The advantages of this route include beautiful Sierra Nevada scenery (gnarly ancient trees, lush meadows, abundant wildflowers, etc.) and the availability of plentiful water. It makes for a fine descent route as well.
From the New Army Pass/Cottonwood Lakes trail head, follow signs as if you are headed for the Cottonwood Lakes. Eventually there is a fork in the trail where you choose between the Cottonwood Lakes and Muir Lake. Turn right, as if you are heading for Muir Lake. However, when you near the south shore of the lake, simply head cross-country to the northwest.
Hike past the numbered Cottonwood Lakes, staying to the right (east) of them, until you reach the unnamed last (northernmost) lake. The Fin is a prominent feature above and northeast of this small lake.
If you proceed to the north side of the lake, you’ll discover a canyon on your left. Head west up this canyon. There is abundant running water here, with lush meadows. The hiking is very pleasant most of the way.
The terrain does become steeper and looser as you approach the western end of the canyon. You might be tempted to scramble up the north side of Peak 3915, which forms the south wall of the canyon. Don’t. It is beyond the typical hiker's comfort level to gain the plateau by scrambling up the north side of Peak 3915 and then continuing west by way of the summit of said peak.
Slog up the final steep portion at the western end of the canyon and emerge onto the immense sandy plateau just south of Mt. Langley. Just turn right (north) and continue to your very obvious destination, now less than an hour away.