This one pretty clearly keys to Kogotus, but it also looks fairly different from specimens I caught in the same creek about a month later in the year. With only one species of the genus known in Washington, I'm not sure about the answer to this ID.
Described by Nelson, C.R. & Baumann, R.W. (1987) New winter stoneflies of the genus Capnia with notes and an annotated checklist of the Capniidae of California (Plecoptera: Capniidae). Entomography 5, 485–521.