The small brushfire burned about a quarter of an acre before flames were put out.
It wasn't until a tow truck was called to move a charred vehicle that the victim was discovered.
"Deputies had the trunk lid forced open, and the apparent human remains of an adult were located inside the vehicle," said Sgt. Martin Rodriguez of the L.A. County Sheriff's Department.
Authorities said they are treating the brushfire and the gruesome discovery as separate incidents.
Anyone with information is urged to call the L.A. County Sheriff's Homicide at (323) 890-5500.