This specimen resembled several others of around the same size and perhaps the same species, which were pretty common in my February sample from the upper Yakima. Unfortunately, I misplaced the specimen before I could get it under a microscope for a definitive ID.
This is the largest common eastern stonefly. It's quite abundant in places, but not to the extent of its western counterparts, and since most of its activity is at night it is generally less important. Nevertheless, nymph imitations produce some very large trout, and lucky or very locally knowledgable anglers may find good fishing to the egg-laying adults.