Fires are not typical in Southern California at this time of year but can break out when dry vegetation and too little rain combine with the Santa Ana winds.
"We realize what an inconvenience this is and how traumatic this is to so many people, but we've watched fires in Northern California, we've seen through experience it's much better to err on the side of safety", Garcetti said at a Wednesday afternoon news briefing.
The Creek Fire continues to burn through southern California, along with three other large wildfires.
The fire was burning in the same general area as the devastating Bel-Air Fire of 1961.
What sparked the Skirball Fire has not been determined.
More than 100 structures - including 56 homes - have been demolished by the fire since it began early Tuesday morning four miles east of Sylmar, officials said.
"We're basically in an urban firefight in Ventura, where if you can keep that house from burning, you might be able to slow the fire down", said Tim Chavez, a fire behaviour specialist at the blaze.
"We've always had fires, and it's always been one of those things, like, 'We'll be OK, '" said Virginia Padilla, Patricia's sister.
Back in the beachside city of Ventura, the fire killed more than two dozen horses at a stable and had destroyed at least 150 structures, a number that was expected to get far bigger as firefighters are able to assess losses.
Evacuation orders first issued Tuesday were affecting about 110,000 households, according to Los Angeles Mayor Eric Garcetti.
The Getty Center and the nearby Skirball Center, both on the west side of the freeway, did not appear to be threatened, though both remained closed Thursday. The 110-acre hilltop campus in Brentwood, which includes the J. Paul Getty Museum and the Getty Research Institute, was designed by the architect Richard Meier with various protective measures against brush fires, to which the region is prone. A full list of closed schools was available at www.lausd.net.
UCLA, Cal State Northridge, Los Angeles Valley College and Santa Monica College canceled classes Thursday.
Los Angeles County sheriff's officials survey damage after the Creek Fire near Sylmar scorched a hillside in a photo released by the Sheriff's Department on December 9, 2017. Almost 500 horses were stabled at the center when the fire started.