The Eaton Fire cause is officially determined: electrical arcing on an out of service Edison tower

On August 4, 2026 the County of Los Angeles Fire Department released the origin and cause investigation into the Eaton Fire, conducted jointly with CAL FIRE under case number 25CALAC-009087. After eighteen months, the fire that killed 19 people and destroyed 9,419 structures in Altadena has an official cause.

The finding. The investigation team concluded that the Eaton Fire was caused by electrical arcing events on an out of service Southern California Edison transmission tower carrying the idle Mesa-Sylmar circuit. The supplemental report places the arcing at the southwest conductor paddle of that tower. The arcing ejected hot metal particles that fell into the dry vegetation below the towers and ignited it.

Video evidence recorded two electrical arcing events in quick succession at approximately 6:11 p.m. on January 7, 2025. The fuel bed ignited approximately twelve seconds after the burning material was seen falling.

Lightning, campfire, and arson were each considered by name and excluded on evidence.

What we published. Two documents were released, both redacted, and the initial fifty five page report is a scan whose text cannot be searched or copied. We downloaded both, read every page, and built a primary source analysis: a hub explaining the determination and seven pages each answering one question, covering the ignition sequence, the three towers and why the idle circuit matters, the elimination of the other causes, the field method that located the origin, why the determination took eighteen months, what the redactions cover, and what an official cause finding does and does not change.

One correction we are making openly. The two released documents do not agree on the casualty and damage figures. The 2025 initial report describes eighteen deaths, more than nine thousand buildings, and over fourteen thousand acres. The 2026 supplemental report, the later document, gives 19 deaths, 9,419 structures destroyed, 1,076 damaged, 14,021 acres and 9 firefighter injuries, and the county press release also says 19. We have updated the Eaton Fire record to the supplemental figures and we state the discrepancy rather than quietly choosing a number.

An origin and cause determination establishes how a fire started. It is an investigative finding, not a court judgment on legal liability. The consolidated civil cases remain before the Los Angeles Superior Court, and the Los Angeles County District Attorney has a separate ongoing review of the evidence, which is the county's stated reason for the redactions.

Read the full official cause report analysis