Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
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.
On our way from the Reno area and the Upper Truckee to fish the Golden Trout Wilderness, we couldn't resist a detour to see the oldest (non-clonal) organisms in the world: the ancient Great Basin Bristlecone Pines and the Methuselah Grove. They did not disappoint.