This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.
Described by Ricker, W.E. & Ross, H.H. (1968) North American species of Taeniopteryx (Plecoptera, Insecta). Journal of the Fisheries Research Board of Canada 25, 1423–1439.