The fire is close to 4,200 acres and has been burning in the Angeles National Forest north of Glendora since Sunday.
There are about 1,100 firefighters battling the flames, with some being flown into the steepest parts of the mountains to cut fire lines.
Dozens of residents who fled the fire are now returning home. The camping area will remain closed this weekend.
Crews hope to have the fire contained by next Thursday. The cause of the fire remains under investigation.View photos of the Williams Fire, burning in the Angeles National Forest.