It is very unusual,and troubling as well.A cave in,bad air in a mine or a rockslide are all possibilities.One other possibility is a large bee swarm,especially if they were well off trail.That is about the only thing that really makes me nervous out there and,depending on the time of year,I've always got my eyes and ears open.I had to make a quick downhill retreat to a creek bottom last April when a large swarm came down a draw towards my position.The sound was near deafening as they paused around a clump of mesquite above me,before moving off down the draw.That was the second such swarm that I have witnessed out there so far.The other possibility,of course, is some form of foul play.Hopefully,that is not the reason for Either Jesse's disappearance or that of these three gentlemen.
Regards:SH.