From the article:

"The Clark County coroner's office attributed 26 deaths to heat stress in 2002 and 4 in 2003. Heatstroke occurs when the body can't cool itself by sweating, and death can occur in only 20 to 30 minutes. Blood pulls away from the heart and brain, causing irreversible brain damage. When heatstroke occurs, it is difficult to reverse the symptoms and prevent death.

To avoid heatstroke, drink plenty of water and avoid hiking during midday in summer.

If heatstroke occurs while hiking, companion hikers should give the victim water and shade, and they should work to cool the large veins in the armpits and thighs."