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 is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominalterga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
This specimen is very tentatively placed in Rhyacophila vocala, but see the caveats given by Dave Ruiter in its identification: "There are two species (hyalinata and vocala) currently within the group and this looks closest to R. vocala. It is likely, however, there are several undescribed species in the group and this is one of those."
There are two species (hyalinata and vocala) currently within the group and this looks closest to R. vocala. It is likely, however, there are several undescribed species in the group and this is one of those.