The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
This is the only Heptageniid mayfly I saw hatch on May 24, 2004, and luckily it floated right by me.
Edit: Gonzo confirmed most likely vicarium 06.21.12
This mayfly was collected from the Namekagon River in Wisconsin on May 24th, 2004 and added to Troutnut.com by Troutnut on January 25th, 2006.