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 Stark, B.P. & Gaufin, A.R. (1976) The nearctic species of Acroneuria (Plecoptera: Perlidae). Journal. Kansas Entomological Society 49, 221–253.