Sounds like it'll be a great trip, Yoseman.
You can get to Sky Blue Lake from Mount Langley by a more direct route than backtracking to Old Army Pass. From the summit, follow the broad southwest ridge of Mount Langley to the saddle just short of the Major General. From there, a wide class 2 chute filled with loose scree descends toward the west-northwest and into the Rock Creek drainage which will lead you to Sky Blue Lake. Secor (The High Sierra, Peaks-Passes-Trails, 3rd ed.) calls this the “West Face” route. I climbed Mount Langley from Sky Blue Lake as a dayhike by that route. I recall that on the descent it was important to be sure and go all the way to the saddle before turning down off the ridge because, other than that one chute, it could get dicey.
Another option, as WanderingJim described, is to backtrack off the Mount Langley summit as far as the drainage to Upper Soldier Lake. Follow that down to below Upper Soldier and take the north fork of the inlet stream of Lower Soldier Lake up and over the ridge into the Rock Creek drainage.
Have fun!
Last edited by Glenn; 01/25/18 09:22 AM.