For eighteen months the Eaton Fire had no official cause. Everyone had a theory, Southern California Edison had told regulators its equipment was a likely ignition source, and the record itself stayed closed. On August 4, 2026 the Los Angeles County Fire Department published the investigation, and the question closed with it.
We downloaded both released documents and read them page by page, including the fifty five page initial report that is largely scanned images and therefore invisible to most automated summaries. What follows is drawn from those pages, with the page and document named for anything material. Where the two documents disagree with each other, we say so and do not pick a winner.
The finding, in the investigators' own terms
The supplemental report signed on July 22, 2026 states the conclusion directly. It is the Eaton Fire Investigation team's opinion that the fire was caused by the electrical arcing events that took place on the out of service Southern California Edison tower. Those arcing events occurred at the southwest conductor paddle of the out of service Mesa-Sylmar circuit tower. The arcing ejected hot metal particles that fell to the receptive fuel beds of dry vegetation below the towers. The introduction of that competent ignition source into the available and receptive fuel below resulted in ignition, causing the Eaton Fire.
Three phrases in that passage carry the weight. Out of service means the circuit was idle, not delivering power, which is the single most counterintuitive fact in the entire record and the reason a separate page below is devoted to it. Competent ignition source is the technical term for a heat source with enough energy, and enough time in contact, to ignite the fuel it lands in. And southwest conductor paddle is the specific hardware, on the specific corner of the specific tower, that the eighteen months of laboratory work was spent identifying.
The initial report, signed more than a year earlier on May 22, 2025, had already reached the electrical conclusion in broader form: the cause of this fire is electrical in nature, caused by an electrical event that occurred at approximately 1811 hours within a grouping of three SCE transmission towers. What the supplemental adds is the precision that only metallurgy could supply.
The sequence
A private security camera on a home on Canyon Close Road recorded the ignition. The homeowner had mounted it years earlier to watch the mountain because of the 1993 Kinneloa Fire, so that his family could evacuate quickly if it ever happened again. According to the video time stamp, at approximately 1811 hours on January 7, 2025, two bright blue and white flashes were seen mid slope. The first flash was brighter than the second. An orange glow follows, described in the report as if it were dripping fire or glowing material. When the second flash happens, more glowing orange material drips and falls toward the ground.
The fuel bed ignited approximately twelve seconds after the burning material was seen falling. Twelve seconds is the entire distance between an equipment fault and the second most destructive wildfire in California history.
Read the full ignition sequence, minute by minute.
The three towers
Residents kept describing fire at the base of "the towers", and the investigation had to pin down which. Three transmission towers sit on a narrow spur ridge above Eaton Wash, running northeast to southwest, and the report labels them by position rather than by SCE's own numbering so that witness accounts could be matched to structures. Tower #1 is the tallest, at the southwest end. Tower #2 is second tallest, northeast of it. Tower #3 is the shortest, north of Tower #2.
Their loads differ, and the difference is the case. Tower #1 supported the Mesa-Vincent #2 and Eagle Rock-Mesa circuits. Tower #2 supported the Mesa-Vincent #1 and Goodrich-Gould circuits. Both carry twelve conductors at 220kV. Tower #3, the short one, supported three conductors for the Mesa-Sylmar circuit, and that circuit was idle. Its conductors run only on one side of the tower and do not continue south. On January 12, 2025, a CAL FIRE battalion chief found a beaded metallic like substance on the interior frame in the southwest corner of Tower #3, near the attached grounding cable. That became evidence item #2.
Why an out of service line could still arc.
What was excluded, and how
An origin and cause investigation is not complete when it finds a likely candidate. It is complete when the alternatives are eliminated on evidence. The report names four scenarios considered: lightning, campfire, incendiary act or arson, and electrical lines.
Lightning was excluded using a Predictive Services lightning discharge map showing no lightning activity in Los Angeles County across the weeks around the fire. Campfire was excluded despite the investigators finding what they judged to be an unauthorized campsite, with rock rings, cooking pots, and the remains of a burned tent, because that site lay roughly 1,200 feet southwest of the origin area and the fire pattern showed fire advancing across it from further up the ridge, not out of it. Arson was excluded because the origin area sits high on a spur ridge unreachable by vehicle, no ignition devices were found, and the one report of a person with a flashlight was investigated and placed more than half a mile away.
The full elimination analysis.
Two documents, fourteen months apart
The most easily missed fact in this release is that it is not one report. It is two, and their signature dates are fourteen months apart.
The initial report was signed by Captain Rick Yartz on May 22, 2025. At that point the field work was finished and the conclusion was electrical, but the physical evidence had not been examined: the report says plainly that the SCE electrical utility equipment was not available for examination, analysis, or testing at the time of the initial investigation, and that data requested from SCE on January 20 and January 31, 2025 had not been received. The supplemental report picks up the story. Warehouse examinations of the removed equipment began in late July 2025. Laboratory testing ran through the latter part of 2025, including a session at a laboratory in Bowling Green, Kentucky between December 9 and December 12, 2025, chosen because its scanning electron microscope chamber was large enough to take pieces the first laboratory could not fit. Metallography followed in Signal Hill on July 22 and 23, 2026, and X ray diffraction in Goleta on July 24, 2026.
The full eighteen month evidence timeline.
What the numbers say, including where they disagree
The two documents do not report the same casualty and damage figures, and we publish that rather than smoothing it over. The 2025 initial report describes a fire that claimed the lives of eighteen people, destroyed more than nine thousand buildings, and burned over fourteen thousand acres, and calls it the fifth deadliest and second most destructive wildfire in California history. The 2026 supplemental report, the later document, gives 19 deaths, 9,419 structures destroyed, 1,076 damaged, 14,021 acres, and 9 firefighter injuries. The August 2026 press release also says 19.
We use the supplemental figures on the fire record because it is the later document, and we note the earlier ones here. A number that changed between two official documents is a fact about the record, not an error to hide.
What is blacked out
Both documents are released redacted. The press release gives the reason: the Los Angeles County District Attorney's Office has an ongoing review of the evidence from this fire, alongside privacy protections under several sections of the Government Code. The redactions are not cosmetic. The entire violations section at the front of the initial report, three Penal Code citations, two Public Resources Code citations, a Health and Safety Code citation, a Public Utilities Code citation and a General Order, is blacked out to the last line. So are the origin coordinates, the tower identifiers, and the names of every retained expert.
What the redactions cover, and what they do not imply.
What this finding is, and what it is not
A fire agency origin and cause determination establishes how a fire started. It is an investigative conclusion reached under a recognised methodology by investigators who can be called to testify about it, and it is evidence. It is not a court's judgment on legal liability, it is not a regulatory penalty, and it is not a criminal charge. Those are three separate processes, and on the public record all three remain open: the consolidated civil cases are before the Los Angeles Superior Court with a first bellwether trial date of January 25, 2027, the California Public Utilities Commission has its own jurisdiction, and the District Attorney's review is the stated reason for the redactions.
What an official cause finding changes, and what it does not.
How to read the documents yourself
We publish links to the original PDFs below and encourage reading them. Note that the initial report is a scan, so the text is not selectable and search will not find anything inside it. The four page supplemental is the faster read and carries the operative conclusion. Both are hosted by Los Angeles County, and the county's After Action Review library is where they live alongside the rest of the Eaton and Palisades record.