Randall Kaufmann's stonefly nymph is a classic Western big-bug pattern. Stonefly nymphs crawl the bottom of rocky rivers for a year or more before hatching, so they are always there for trout to eat. This fly imitates that meaty, year-round food. The dubbed body, picked-out legs, and shaggy profile read as a clumsy stonefly nymph tumbling in the current.
Tie or buy it in two colors: black for the salmonfly nymph, brown for the golden stone. Sizes 6-8 cover salmonflies, 8-12 cover golden stones. It is a heavy fly, usually weighted with lead wire under the body, because it needs to ride right on the bottom where the naturals live.
Fish it dead-drift along the riverbed, with enough weight or split-shot to tick rocks as it goes. It works best in normal-to-high flows from clear to off-color water, and in water from the low 40s into the low 60s - prime stonefly season. Run it as the point fly on a nymph rig with a smaller mayfly nymph dropped off the back.