The California Highway Patrol is investigating the death of a 75-year-old driver found inside a pickup on a dirt road in Bonsall Saturday afternoon, officials said.

The driver and two passengers were in the truck when it got stuck while backing up on Shirey Road near Rocking Horse Road, east of Interstate 15, according to the California Highway Patrol.

The passengers left to go get another vehicle to help free the truck while the driver stayed with the pickup, said Sgt. Benjamin Demarest.

Upon the passengers’ return, they found the pickup engulfed in flames with the man inside around 1:40 p.m., he said.

Cal Fire firefighters put out the fire in the truck and also a small area of brush that burned, officials said.

The CHP is investigating the fire, a Cal Fire spokesperson said. The name of the man who died was not immediately released.

City New Service contributed to this report.