Zen, I fished Alaska Lake back in the early 90's a couple times. Had a nasty hard to follow trail from in behind Hyak up Gold Creek Valley. Not sure you can even access it that way any more, but you can get there off the crest trail too by hiking down steep slopes w/o trail when you spot it.
It's full of nice Cutts including I suspect some big ones though all I cought were 11-14".I got rained on hard despite a good forecast the last time in there. Very unpredictable weather along the Cascade Crest Mts.
I'm anxious to hit Sprague right after ice out. The big carryovers in there (#3-#5)come into one particular shallow bay after the first hatching chronies in the spring. Almost no one fishes them with flies.
I'm gonna try it this year.