It's 4 p.m. in Joshua Tree National Park and the air temperature is hovering around 99 degrees -- relatively mild for an August afternoon. But at ground level, the sand along the popular Hidden Valley Nature Trail has reached a scorching 136. "I don't want my bare feet on that," says ranger Anna Marini as she shows her thermometer gun reading to a couple visiting from Switzerland, who are appropriately awed. Marini uses the tool as a prop to engage hikers traversing this surreal desert wilderness that's roughly the size of Rhode Island. As the coordinator of the park's Preventative Search and Rescue Program, her mission is to protect visitors from hazards that include extreme heat, razor-sharp cacti and thirsty bees.

An exhaustive search is underway for an Orange County couple reported missing Friday after they failed to return from a hike in Joshua Tree National Park. Rachel Nguyen and Joseph Orbeso, believed to be in their 20s, never checked out of their Airbnb accommodations on Friday and left all of their belongings behind, said Dan Messaros, incident commander for the search. After the pair were reported missing, authorities found their vehicle near the Maize Loop trail, a northwest area of the park. A ping from Orbeso's cellphone was also recorded about 4 p.m. Thursday from an area in the park. Authorities believe the couple went for a hike in the area, he said. Nguyen and Orbeso have not been seen or heard from since, Messaros said.