It had escaped my notice the first time around, but this is actually Isonychia tusculanensis. Notice the branched veins connecting the Cu vein to the anal margin and the obtuse costal projection of the hindwing. According to Kondratieff and Voshell (1984, see description and wing illustration), this species “has only been collected in the Appalachian region of Tennesee and Virginia.” (Radford is in this region, and several records come from Yellow Sulphur Springs in adjacent Montgomery County.) Curiously, they also recount that “males of I. tusculanensis were once collected swarming in company with Leptophlebia nebulosa….[males of] Both species have apical regions of the forewings shaded with brown.”

Thanks for the updated ID.
Am I seeing correctly that my little mayfly now has its own page?

You're the first to contribute images of this species!