The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
This specimen was collected together with a lighter one of the same species.
It resembles another specimen from about 1300 miles away in Wisconsin, which I tentatively called Ephemerella needhami. This one has much less prominent abdominal tubercles. It may be that they're both the same species and I don't have my identifications straight.