Firefighters responded to the area of Gilbert Street and Castlewood Drive shortly before 8 p.m., with police announcing homes were being evacuated.
Fullerton police said at around 9:45 p.m. the fire was at 8 acres and was contained in the northeast corner of Gilbert Street and Castlewood Drive, adding that no homes were at risk of burning. Residents who fled the area by foot were allowed to return to their homes before 11 p.m., but roads will remain closed to vehicular traffic as firefighters continued controlling the blaze.
A flare gun was found at the scene and is part of an arson investigation.
Fire officials at one point said the blaze had burned at least 20 acres.
Evacuations were issued for the following areas:
MANDATORY EVACUATIONS
-1700 block of Deerwood
-2100 block of Dalewood
-1700 block of Summerwood
-2200 block Ardemore
-2200 Pickwick Pl
-1700 block of Berkshire
-All of Chantilly
-All of Somerset
-All of Brooke Lane
-All of Walker Lane
EVACUATION CENTER
The Fullerton Community Center, 340 W. Commonwealth Ave.
Gilbert Street is closed from Rosecrans Avenue to Imperial Boulevard.