Forgive my ignorance but how the h-ll do you get lost AND un-locatable in a desert? A National Park no less. Use the sun to walk in roughly the same direction, eventually you'll hit a road? If they're injured and in the shade of a rock, at least make a big circle in the dirt nearby for the helicopter? Maybe I'm being harsh but I've never found myself in a position where I went off a trail and lost track of where I was, and I'm usually in the forests. Nobody really taught me to keep track of what direction I'm going... I thought it was second nature to all mammals? I guess it's different for city folk.