A few months ago, an extremely fit and experienced desert hiker attempted a run in the Grand Canyon and ended up dying in the middle of it. The onset of heat illness was so quick, that she was unprepared to deal with it and didn't act in time to save herself -- probably never realized what serious trouble she was in.

On MY first hike to Supai (also a Grand Canyon-area hike) I hiked in the early morning hours (in what was probably 90 degree temperatures in the sunlight) -- but the hike was in shade for many parts of the way -- and I carried plenty of water. BUT, because I was comfortable and didn't seem thirsty, I didn't DRINK the water -- I hiked -- and I hiked fast, for about three hours.

By the time I covered the 9 miles to the village, I was suffering from heat sickness and collapsed in a heap at the tourist office on my arrival there. Again, it happened so quickly that had I still been on the trail, and in a place without shade, I would have been in serious trouble. As it was, my recovery took almost an hour, and I felt terrible for two or three hours after that. I finally recovered by sitting in the cold waters of Havasu Creek, under the kind ministrations of a couple of very fine school teachers.

The point is that desert heat is nothing to fool with -- a person is smart to take the advised precautions seriously and religiously.

The other "rule" that comes to mind is if you are not prepared to break down in the desert -- don't go off-road. Those of us who live in desert areas drive around all the time, most without any thought of the dangers -- but the smart ones among us keep basic survival items in the vehicle all the time -- these become an absolute requirement for any off-road adventures -- in many, many parts of the southwest, you can literally disappear within a few feet of a main roadway -- some of them are so little-traveled that no one EVER goes out there (and if you are not a local, you won't know which roads those are). If you go off-road, you have to be prepared with all the tools and materiel you need to rescue yourself, including plenty of drinking water.