This specimen resembled several others of around the same size and perhaps the same species, which were pretty common in my February sample from the upper Yakima. Unfortunately, I misplaced the specimen before I could get it under a microscope for a definitive ID.
Described by Nebeker, A.V. & Gaufin, A.R. (1965) The Capnia columbiana complex of North America (Capniidae: Plecoptera). Transactions of the American Entomological Society 91, 467–487.