Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
This female dun emerged from a creek loaded with mature Cinygmula nymphs including this specimen, so they're probably the same species. Unfortunately there aren't species keys for either stage.
This mayfly was collected from Green Lake Outlet in Idaho on August 4th, 2020 and added to Troutnut.com by Troutnut on August 20th, 2020.