I recently ran what I have called the Bryce Canyon Link-Up. With a friend, we connected all three back country trails in Bryce Canyon and did them as a run.
We started at Rainbow Point and ran the Riggs Trail, then Under-the-Rim trail, and ended on the high side of the Fairytale Loop trail. I intended to do the lower, longer half, but my friend had a hurt knee and I was just anxious to get it over with.
I tried to do some research but couldn't find anyone else who has ever done this.
It turned out to be 37 miles in a time of 8:31:17.
It is a really soft time and could be easily beat. One of the coolest runs I've ever done though.
Trip report can be viewed at refusetoquit.blogspot.com/2010/06/bryce-canyon-link-up.html.