The Los Angeles Fire Department says the fire broke out just before 6 p.m. and burned through three acres. Early reports said the flames had jumped the freeway but firefighters on scene said it hadn't.
Several homes in the vicinity were threatened but crews managed to keep them intact.
People in the area posted photos on social media showing big plumes of white smoke and flames burning on a hillside near a gas station.
Crews extinguished the flames in less than two hours, as it was tackled by both ground and air teams.
Officials said the department's Arson-Counter Terrorism Section is investigating the fire.
It's still unclear if the suspect detained by Los Angeles police is "connected to the fire or other potential crimes in the vicinity," according to a statement from LAFD spokeswoman Margaret Stewart.