I talked to a park ranger near the site where the body was found, and this ranger was there on the day they recovered the body.

When I was at the site where they found him, there were many tourists hiking in the area with nothing but one water bottle, in shorts, sandals, some with hats. It was 116 degrees F, clear sky and very strong sun. The arroyos in the area are very steep and one could easily stumble or slip into one. There would be no visibility from the observation point into the bottom of most of them, so without the ability to signal it is unlikely someone would see you from where most of the tourists were. The same scenario could play out again very easily.