Even though the Painted Desert and the Petrified Forest are higher in elevation and will be somwhat cooler than, say, Phoenix, it will still be HOT! If you plan on doing ANY hiking, be sure to take LOTS of water with you...at least one gallon per person. Wear a hat and put on sun screen. The Southwest during the summer, even at higher elevations, isn't anything to take lightly. You'd be surprised at how many people have to be rescued from the trails in the Grand Canyon each year, mainly because people didn't have enough water with them.