Too bad about all the traffic between Challis and Stanley, as that's one of my favorite rides in Idaho. Fishing season really brings out the crowds here. Next time you're in the area, head north from Challis towards Montana, as there's some fine twisties and scenery.
It is a bit boring for a while coming from Stanley towards Lowman on 21, but the scenery is at least nice. The fun bits, if there is no traffic, are really fun.
The run from Lowman down through Idaho City and then to Boise is plenty twisty, if more than a bit bumpy in places, and a regular run for those of us in the area. Lately, though, very heavy LE presence has kept me off hwy 21.
Glad you didn't encounter the critters which abound in Idaho. Deer, elk, coyotes, even moose and cattle are not uncommon in the areas you rode through.
Nice pics and commentary, look forward to reading about the rest of your ride.