Two seniors set off in the desert for a walk/hike. You would hope they would both be adequately dressed for the heat. The man has a bag (presumably would contain water for them both, sunscreen and (if they were not wearing them) shirts to cover their shoulders in the hot sun, phone, key for the camper and possibly any medications they can't be without.
So, after their walk, when it was time to go back, the husband stops to take a pic - so he uses his phone right? Or… does he unload a a tripod, camera etc - all this equipment that he has been lugging around during their walk just to get the perfect picture of rocks?
The wife decides she can't wait for him to take his picture and wants to go back to the camper. He says this will only take a minute, don't go back by yourself, it's not safe to be out in the desert alone, or did he say, go back by yourself, I'm busy taking a very important picture, here's the key … oh wait, I left the key under a rock, just in case something like this happened.
In the short time that he is occupied, his wife disappears into thin air, never to be seen again.
The husband can't figure out what happened to her. Was some stranger driving past at exactly the same time as his wife (who was, for some reason dressed in a black bikini and carrying a beer) was crossing the road? Was the stranger so enamoured by her appearance, that he decided to stop and grab her? In any event, she never did reach the key under the rock and the safety of their camper.