Pat's Rubber Legs - the "pickle" to a lot of guides - is about the simplest deadly fly in the box: a fat chenille body and a tangle of rubber legs that wiggle on their own in current. It imitates stonefly nymphs, the big crawlers that live a year or more on the streambed before they crawl out to hatch. It covers both the salmonfly and the golden stone, the two biggest stones a trout sees, and it works year-round since those nymphs are always down there.
Tie it in sizes 4-10. Black and coffee read as salmonfly nymphs; brown and olive read as golden stones. Go bigger and darker in spring high water, smaller and lighter as flows drop and clear.
This is a bottom fly, so weight it - heavy hook, a bead or wire wraps, plus split shot if you need it - and get it down. Dead-drift it through deep runs and along the seams, riding right on the gravel where the naturals crawl. It earns its keep from 42-60F and anywhere the water runs normal to high and clear to off-color. Run it as the point fly on a two-fly rig with a smaller mayfly nymph trailing behind.