I went up to Mammoth a few weeks ago and experienced the same thing I and most everyone I go up there with have experienced every time we go. We call it the Mammoth Effect. Why is it that when we get up there we fart so much? Our theory is, the gases will expand as they reach higher altitude and this is the "gassing off" of everything we walk around with down here at sea level.
--Karlos, the net
Do you realize that your tax dollars went to NASA to study high-altitude farting? Well, it did. In fact, there's been a suspiciously large amount of research into the subject. Some medical students even walked around for several days with tubes in their butts having their farts collected, measured, and analyzed. But anyway, because of all this interest, we can say with some certainty that the higher the altitude, the lower the atmospheric pressure, and the larger your internal gas bombs will grow. Not with added gas, just the same amount expanding to fill more space. The highest ski lift at Mammoth runs to about 11,000 feet. At this point, your gut gas has expanded to about 130% of it's sea level displacement. The increased pressure finds the path of least resistance, and the princple of jet propulsion kicks in. Avoid cliff edges for the first few days.
Mammoth itself has a gas problem. As an old volcano, it seeps and burps CO2 and hydrogen. They think that's what's been killing trees in the area, but maybe it's really the Mammoth Effect from all those tourists.