Noted recently (December 2016) that in that month alone there were two "gravity poisoning" events at the South Rim alone. Just another example that falling is one of the two main causes of outdoor fatalities. The other is drowning, and you can accomplish "hydraulic poisoning" at the Canyon as well.
Having worked a career with the NPS, I am aware of the tremendous range of outdoor knowledge, or lack thereof, in people who visit parks. All too many folks haven't the beginning of a clue about how to stay alive, much less safe, when out of the city.
Geezer in Chief