The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.
John-
The leg colors you mention are pretty typical of Isonychia. Wetzel's "white-gloved howdy" name referred to the white-tipped front legs of the bicolor female, held out as if awaiting a greeting handshake. (I love that name!)
Roger-
This certainly looks like Isonychia to me. There are several Iso species with a southern distribution, so I won't hazard a guess about species.
I'm also not 100% positive it's a female, since the rear end is pretty blurry. Males in Isonychia have unusually small eyes.