Lots of these perfectly preserved exoskeletons on the dry rocks next to the river. We had hundreds invade our campsite the night before. They were all a tan/silvery color not like the black ones from a few months before.
That's a Summer Stonefly, Claassenia sabulosa. Short-Winged Stonefly, I've hatched these guys out of my aquarium. Females have normal lengthed wings, while the males have short wings, and those males crawl at a million miles an hour, bad idea hatching them.