Great info, NightHiker; thanks.

I'd like to point out something about operating in extremely high temps i.e. Death Valley during a heat wave. It is certainly wise and true to carry and drink plenty of fluids. But I think some people get the idea that if they just stay hydrated, the heat won't hurt them. This is not true.

If it is hot enough combined with your activity level and personal factors, you can be perfectly hydrated and still die of heat stroke. It becomes a matter of heat gain and loss. If the environment is heating your body beyond the rate at which you can cool yourself, you will get a net heat gain. If this gain heats your brain beyond a certain point, you get heat stroke and die.