A French couple died while hiking in New Mexico’s White Sands National Monument last Tuesday, but their nine-year-old son survived, according to CNN. David and Ornella Steiner, of Bourgogne, France, were visiting the Southwest with their son. The trio hiked into the shadeless desert of sand dunes off Highway 70, between Las Cruces and Alamogordo, where they suffered from heat exhaustion. Rangers say they discovered the son in decent shape while on a routine patrol last Tuesday.

“The parents would take a drink, give him two drinks. They would take a drink, give him two drinks,” Otero County Sheriff Benny House told CNN affiliate KVIA. “I’m sure that’s a contributing factor on how he fared so well.”

Officials at White Sands have urged visitors to carry one gallon of water per person when hiking in the desert. The couple was carrying two 20-ounce water bottles when they began their hike on the Alkali Flat Trail shortly after midday, according to the AP. Ornella appears to have separated from the group and turned back, only to collapse about 100 yards away, while David, likely unaware that she was in trouble, collapsed about 2,000 feet down the trail.

After being treated for dehydration at a local hospital, the Steiners’ son was reunited with relatives, including his grandmother, who arrived in Albuquerque on Thursday.