The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
This Skwala nymph still has a couple months left to go before hatching, but it's still a good representative of its species, which was extremely abundant in my sample for a stonefly of this size. It's obvious why the Yakima is known for its Skwala hatch.
I believe (what you refer to as the dun) is actually a male imago of genus Isonychia
I also believe (what you refer to as a Hendrickson), which is a common name often used for Eastern Ephemerella, is probably of genus Drunella.
The next time you photograph a mayfly nymph, I suggest using a pickle jar lid, and filling it with enough water to completely cover the nymph. That way, the body appendages will stand out, as opposed to being all stuck together.