The blaze was reported shortly before 2 p.m. near North Pinnacle Lane.
The flames blackened a large swath of the hillside before firefighters arrived at the scene.
The fire burned at least five acres, with the potential to consume at least 50 acres, according to the San Bernardino County Fire Department.
No injuries or structural damage were immediately reported.
Crews reported stopping the forward rate of spread of the blaze around 3:14 p.m.
Firefighters remained at the scene to extinguish hot spots.