MOJAVE, Calif. (AP) – Rescue crews in Southern California are on their fourth day of searching for a 69-year-old hiker who went missing in the Mojave Desert amid soaring temperatures.

San Bernardino County authorities say Tuesday there have been no sightings of Bullhead City, Arizona, resident Barbara Thomas, who went hiking with her husband Robert on Friday. The two got separated around 2:30 p.m. near the area of Kelbaker, about 20 miles (32 kilometers) north of Interstate 40.

She was wearing a black bikini, a red baseball cap and tan hiking boots with black socks, but was not equipped with any other supplies or a cell phone.

Temperatures have hovered around 100 degrees since Thomas has been missing.