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 DeWalt, R.E., Stark, B.P. & Harris, M.A. (1998) Perlesta golconda (Plecoptera: Perlidae), a new stonefly species from Illinois. Entomological News 109, 315–317.