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 Frison, T.H. (1942) Descriptions, Records and Systematic Notes Concerning Western North American Stoneflies (Plecoptera). The Pan-Pacific Entomologist 18, 9–16.