I associated this female with a male I collected one night later. For a great and informative discussion of all
Epeorus species and other mayflies be sure and read, WESTERN MAYFLY HATCHES by R. Hafele and D. Hughes. They rate all of the western mayflies and they rate the hatch of this genus a 25 out of a possible 45 points based on several rating criterion. They provide insect photos, possible fly patterns and fly presentations. This is a great book.
Edit by Troutnut: Bob generally knows his IDs better than I do, but I think this one was misidentified as
Epeorus longimanus. The darkened
humeral crossvein is not supposed to be present in
longimanus. I'm moving it up to
Epeorus.