The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
These duns were emerging sporadically throughout a cloudy evening at the end of June. Had I looked more closely when I caught this one and realized it represented my first collection of this genus, or just noticed the really striking coloration, I would have set my fly rod on shore and spent more time lurking mid-river with my net trying to catch more of them emerging (and at least one in better shape).
It's always a bit difficult to identify a female dun, but in this case the three longitudinal stripes on the sternites are very distinctive and narrow the choices to Caudatella heterocaudata and Caudatella columbiella. However, the length of the fore wing measured with a caliper is 7.25 mm, whereas columbiella should be no more than 6 mm, so heterocaudata appears to be the correct ID.