California authorities are looking for a 69-year-old female who has been missing while walking in the Mojave Desert. Barbara Thomas, a resident of Arizona, has no means of surviving the sweltering heat anticipated this week, the office of the San Bernardino County Sheriff said.

Thomas was last seen on Friday wearing a black bikini, a red baseball cap and tan hiking boots with black socks. She was separated from her husband as they hiked about 20 miles north of the Interstate 40 freeway.

Temperatures in the Mojave Desert exceeded 100 degrees over the weekend and are expected to remain in triple digits this week. Thomas did not have a cellphone or any supplies with her, authorities said.

There have been no sightings of Thomas, who is 5-foot-9 and 130 pounds, the sheriff’s office said. Anyone with information on her whereabouts is asked to contact authorities.