The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
I looked at this nymph closely under my crappy microscope. It has truncate as opposed to rounded gills, postero-lateral spines only on abdominal segments 7-9, and oblique crossbars through the center of each sterna, not on the posterior edge like on some of the other Maccaffertium species. As best I can tell from the keys this is either modestum or ithaca and from the distribution maps I've seen I'm guessing it's modestum.
This mayfly was collected from unknown in Wisconsin on March 10th, 2004 and added to Troutnut.com by Troutnut on January 19th, 2006.