Nine Mile Canyon, or I wasn't paying attention. Luckily for me, a post about it showed up on my Facebook feed. Rats. I had passed by both access points during this year's summer ramblings. I'll definitely go next year, even though the Edward Abbeys of the world hate the fact the place is vehicle-accessible.
Also, as I read Wallace Stegner's Beyond the Hundredth Meridian, (e-book in one hand, map in the other) I keep thinking of the places in Utah I need to see again with a more informed eye.