LOS ANGELES — As the charred hills of the Pacific Palisades continue to smolder and rainstorms approach, investigators are racing to uncover the origins of the devastating Jan. 7 fire that claimed 11 lives and destroyed more than 6,800 structures.

Covering up to 10 miles of terrain each day, they have amassed more than 235 leads in their search for answers, with attention turning to a suspicious fire that started days earlier in the same area.

The investigation has zeroed in on a scorched ridgeline above an exclusive neighborhood known as the Highlands, a community perched in the mountains overlooking the Pacific Ocean. This area is near the site of a smaller blaze that the Los Angeles Fire Department said was contained in the early hours of Jan. 1, just six days before the catastrophic Jan. 7 fire erupted.

Earlier this week, yellow caution tape blocked off access to a trailhead linking the Highlands to a popular hiking area in Topanga State Park. Many houses surrounding the trail were untouched by the inferno. But just blocks away, the scorched remains of once grand homes and blackened trees dotted the landscape.

Some 75 personnel from local, state and federal agencies have fanned out around the state park, known for its stunning views of the ocean and popular landmarks like the eponymously named Skull Rock boulder and little Buddha sculpture.

Both are points of particular interest in the investigation because of their proximity to the two fires, according to the Bureau of Alcohol, Tobacco, Firearms and Explosives’ Los Angeles office.

The Los Angeles Fire Department referred all questions regarding the Jan. 1 and Jan. 7 fires to the ATF.

Following the clues

No homes were damaged or destroyed in the Jan. 1 fire, but investigators with the ATF are exploring possible connections to the Jan. 7 inferno. They are also looking into other human causes like arson, fireworks and unauthorized camping activity.

The fire is more than 84% contained as of Sunday. It has so far burned more than 23,440 acres and flare-ups have continued to spark nearly three weeks later.

“We’re not leaving any stoned unturned,” Ginger Colburn, an ATF spokesperson, said outside the agency’s makeshift command center on the Pacific Coast Highway. While Colburn declined to confirm a direct link between the fires, she emphasized that investigators are analyzing all the data and added that there “isn’t any reason not to go back” and look at both incidents.

Highlands residents reported hearing fireworks on New Year’s Eve before a small fire broke out in the wildlands bordering the neighborhood. Firefighters responded to a call from a resident who lives about two blocks from the Skull Rock trailhead shortly after midnight on Jan. 1. By 5 a.m., that fire was out and firefighters remained on the scene afterward, according to NBC Los Angeles and residents who saw and heard fire crews hours later.

That fire was largely forgotten until Jan. 7, when smoke was again spotted in the mountains and canyons surrounding the Highlands. Firefighters responded to a call from a different resident who lives about a three-minute drive from the address of the caller who reported the Jan. 1 fire. Both homes have backyards that face the Temescal Ridge Trail, one of several local hiking trails leading to Skull Rock.

Now, investigators from local, state and federal agencies are piecing together a complex puzzle. They have reviewed over 85 hours of video footage and combed through social media posts from hikers and park visitors, Colburn said.

Anatomy of a fire investigation

Amy Masi, a fire investigator with the U.S. Forest Service not involved in the case, described the painstaking process that forensic experts undertake.

“To figure out the cause and origin of a wildfire, a method is used that is similar to solving a mystery,” she said.

The Forest Service, which trains the ATF on wildfire analysis, has three investigators working alongside the bureau on the Palisades Fire probe.

Like police detectives, fire investigators observe the scene and narrow down their search area, ideally to a 25-square-foot area, according to Ed Nordskog, a retired Los Angeles County sheriff’s fire investigator not involved in the case.

Then they divide the area into a grid of zones each measuring about 4 square feet. Investigators collect evidence that could include footprints, campfire remains, lighting strike ash or burned electrical equipment, he said.

With the help of magnets, metal detectors and magnifying lenses, investigators search for even the smallest pieces of evidence, such as fragments of molten machinery parts, match heads, glass and remnants of fireworks.

Specially trained dogs sniff out traces of accelerants and investigators carefully follow nearby electrical equipment, like fences or poles, or signs of gas-powered vehicles, which are more likely to overheat and spark a fire than electrical vehicles. Evidence is then sent to a research lab for processing to determine how long it’s been there.

“Fire science is just that. It is a science, but there’s an element of art to it,” said Scott Sweetow, a former ATF fire investigator. “People assume that fire destroys everything. It doesn’t.”

Burn patterns on rocks, brush and debris hold clues for investigators, who can determine how the fire moved and trace it back to its point of origin.

The process can be daunting, said Matt Brossard, a former investigator with the Forest Service who is now a business representative with the National Federation of Federal Employees.

Brossard, who is not involved in the investigation but helped train ATF agents in wildfire analysis, said examining an area like Topanga State Park can be especially complicated because of its topography and popularity.

“If there’s any physical evidence left, that depends on weather conditions and the materials first ignited,” he said. “If it’s in the grass, we have a very easy time finding stuff in grass and heavy brush. But where the heat is much, much hotter, your evidence deteriorates because it’s burning for a longer and more intense period of time.”

Unusually dry conditions leading to the Jan. 7 conflagration and the six days between the first and second fire could hold important clues for investigators. Embers can lodge deep within tree roots and get covered by heavy ash. In that scenario, embers could continue to burn underground and become dislodged during a heavy windstorm, Brossard said.

The Forest Service uses infrared technology and other techniques to monitor fires under brush for days or even weeks after they are contained, he said.

But the relatively light vegetation of the Pacific Palisades landscape and the six day-stretch before the Jan. 7 fire make rekindling “very unlikely,” Sweetow said.

“It’s a question a lot of people have,” he said. “Our investigators are certainly going to have it.”