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.
Coxa: The basal segment of an arthropod's jointed leg; comes from the Latin word for "hip." Although a part of the leg, it may look more like a socket on the body to which the "actual" leg connects.
These other words reference the same concept: coxae, coxal.
