The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
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.
This stonefly was collected from Mystery Creek #199 in Washington on June 19th, 2023 and added to Troutnut.com by Troutnut on June 21st, 2023.