The blaze dubbed the Grand Fire was 70 percent contained Saturday after charring 4,300 acres.
Firefighters say lower temperatures and higher humidity helped them overnight.
Hungry Valley State Park and Piru Creek Recreation area remain closed. Frazier Mountain High School was also closed as a precaution.
No homes or buildings were threatened but crews said containing it would be a difficult task due to the very difficult terrain.
The blaze which broke out near Interstate 5 on Wednesday initially burned thick brush, season grasses and sage, but then moved into trees. It started at about 300 acres but quickly spread to 3,000 in just a few hours.
The cause of the fire remains under investigation.
