Confidence: It might be this.
Notes: I think that this is one of the two species of Perlid stoneflies. Large stonefly - am I right that this is about an inch long and quite bulky? Hard to tell from the picture, but the only other stonefly species of that size, Perlodes microcephala, usually has an orange stripe on the head and thorax. This is a male - in several species males often have reduced wings as is shown in this image.