You will need a car if you plan to visit the national parks. There is no public transportation inside the parks. From May through September temperatures often exceed 105 degrees.
Nights are considerably cooler than days year-round.
The National Park Service, nps.gov . Just months after the death of her husband, Elisabeth Stager had joined my husband, Chris, and me on a trip across, up, down and around Arizona. Escaping New York, we flew into Phoenix and rented a car. Armed with a couple of guidebooks and recommendations from friends, we picked a destination each morning, booked a motel room in advance, and hit the road, sightseeing along the way. Our first destination was Lukeville on the Mexican border, our base for two days of visits to the Organ Pipe Cactus National Monument in the Sonoran Desert.