Officials have traced the origin of the wind-driven blaze in Pacific Palisades to an area behind a house on Piedra Morada Drive, which overlooks a densely wooded arroyo. The hilly neighbourhood is home to Hollywood stars like Jamie Lee Curtis and Billy Crystal, who lost their houses in the fire.

Lightning is the most common cause of fires in the U.S., according to the National Fire Protection Association, but investigators quickly dismissed it as a factor. There were no reports of lightning in the Palisades area or in the surrounding terrain of the Eaton Fire, which started in east Los Angeles County and has already caused the destruction of hundreds of homes.

Intentional fires and utility line sparks are the next two most common causes.

John Lentini, owner of Scientific Fire Analysis in Florida, who has investigated major fires in California, including the 1991 Oakland Hills Fire, emphasized that the size and scope of a blaze do not change the approach to determining its cause.

“This was once a small fire,” Lentini said. “People will focus on where the fire started, determine the origin and look around the origin and determine the cause.”

There has been no official indication of arson in either fire so far, nor have utility lines been identified as a cause.

Under California law, utilities must report any “electric incidents potentially associated with a wildfire” to the California Public Utilities Commission, said Terrie Prosper, the commission’s communications director, in an email. The CPUC staff then investigates to determine if there have been any violations of state law.

The 2017 Thomas Fire, one of the largest in California’s history, was caused by Southern California Edison power lines coming into contact during high winds, investigators found. The fire killed two people and scorched over 440 square miles (1,140 square kilometers).

On Friday, Southern California Edison submitted a report to the CPUC regarding the Eaton Fire in the hills near Pasadena, an area served by the utility.

While Edison said it has not been notified of any involvement of its equipment in the fire’s ignition, the company filed the report with state utilities regulators as a precaution after receiving evidence preservation notices from insurance company lawyers.

“Preliminary analysis by SCE of electrical circuit information for the energized transmission lines going through the area for 12 hours prior to the reported start time of the fire shows no interruptions or electrical or operational anomalies until more than one hour after the reported start time of the fire,” the utility reported.

Lightning, arson, and utility lines are the most common causes of fires, but debris burning and fireworks also contribute frequently.

Fires can also be sparked by a variety of other sources, including accidents.

In 2021, a gender reveal stunt sparked a massive fire that burned nearly 36 square miles (about 90 square kilometers), destroyed five homes and 15 other buildings, and led to the death of firefighter Charlie Morton.

As of Friday, the Eaton and Palisades fires were still raging with limited containment. While winds had eased, no rain was expected, and the flames continued to spread across miles of dry land.

“It’s going to go out when it runs out of fuel, or when the weather stops,” Lentini said. “They’re not going to put that thing out until it’s ready to go out.”