Hard to tell where the action will be. Some years ago my brother and I ran North Rim to South Rim, Grand Canyon with a group of runners from Houston. We left about dawn, breaking up by design in to a fast group and a slow group. Bro and I were in the fast group and we were essentially the medical talent (Bro is an MD; I am an EMT) By the time we reached Indian Gardens, just before the last push to the South Rim, we decided to wait for the slower group just in case anyone was in trouble. So we had a nice hour interlude before finishing the run.

What we didn't know until we reached the rim was that one of the fast group had cratered, was in some difficulty, and just barely eked his way out of the canyon with a bit of assistance.