A cause determination is only as strong as the alternatives it eliminates. The Eaton Fire report contains a section headed Cause Consideration that names the scenarios considered, and a section headed Eliminated Ignition Source that works through them. Because the campsite rumour circulated widely in the eighteen months before release, this analysis is worth reading in full rather than in summary.
The four scenarios
The report states that efforts were conducted to determine the specific action, or inaction, that caused the competent ignition source and the first fuels to come together. The fire cause scenarios considered were: lightning, campfire, incendiary act or device (arson), and electrical lines.
That framing is standard practice under the National Wildfire Coordinating Group methodology the team used. You do not select a cause. You identify the origin area, inventory every ignition source that could plausibly have existed inside it, and eliminate each one on evidence until the remaining hypothesis is supported.
Lightning
The shortest of the three eliminations. The investigator reviewed the Predictive Services Lightning Discharge Map covering the period around the fire and observed no lightning activity in the general origin area of the Eaton Fire. A separate note in the January 16, 2025 entry records that the map provided showed no lightning strikes within Los Angeles County from December 17, 2024 to January 8, 2025. Lightning was considered as a possible cause and excluded.
The value here is the window. A map covering only January 7 would leave open the possibility of a holdover fire smouldering from an earlier strike. A window running from mid December closes that.
The campsite
This is the one that mattered publicly, and the investigators did not dismiss it. They found it themselves, on the second day, before they had a cause.
On January 8, 2025, descending the spur ridge, the lead investigator saw what looked like a campsite on a mesa to the west and went to it with Captain Milloy. What they found is documented in detail: a rock ring, whole bananas, food in a pot, various cooking pots, metal cans, and fiberglass poles in the shape of a square, which suggested to them that a tent had been burned. A second rock ring and the remnants of fiberglass poles lay approximately ten yards west of the first, and a third area approximately ten yards southwest of the second, also with fiberglass pole remnants.
They drew the obvious inference about its nature. Based on the contents observed at the sites, it appears that it was not likely a recreational campsite, and recreational camping is not allowed within Eaton Canyon. In the later elimination section the same site is described as likely an unauthorized campsite.
So a campsite existed, and the investigators said so. It was excluded on two grounds, and the first is the decisive one.
Geography and fire direction. The campsites are approximately 1,200 feet southwest of the middle towers. The fire pattern indicates a predominantly advancing fire that progressed across the mesa to the west, indicating that the fire originated further up the spur ridge north of the campsite. Fire direction is read from physical indicators on the ground: angle of char on trees, sooting and staining on rocks, protection, grass stem fall, freezing, spalling, curling, cupping, and U or V patterns. Those indicators showed fire arriving at the campsite from higher ground, not leaving it. A fire that starts at a campsite spreads outward from the campsite. This one crossed it.
No recent use. Inside the origin area itself, the investigator did not locate any signs of recent human activity or a recently used campfire. The Eaton Canyon trailhead was closed on the day of the fire, the park is day use only with no camping, and no vehicle roads lead to the origin area.
The team also worked the question through people rather than only through the ground. A Los Angeles County Natural Area Biologist who worked out of the Eaton Canyon Nature Center on January 7 said she did not know of anyone camping or living in the park, that the park had no game cameras on the trails, that the park was closed for the day because of the wind, and that when she left at 1730 hours there was no suspicious activity. A County Parks employee who had worked the park since April 2024 was not familiar with any transient activity deep into the wash area. Sheriff's deputies from the Parks Bureau were asked to identify anyone camping in Eaton Canyon: one deputy had a single reference to a person experiencing homelessness who had been removed from the park roughly a year earlier, and a background check on that individual revealed no criminal findings. Another deputy said he had trespassed people from the park approximately two years prior and was not aware of anything recent.
Arson
The elimination rests on access, absence of devices, and absence of indicators.
The report defines the category, then applies it: the origin area was located high on a spur ridge that is unreachable by a motor vehicle, the investigator did not see any indicators of recent human activity, and did not find any ignition devices commonly used by arsonists. On that basis arson or incendiary cause as a possible cause was excluded.
Two specific reports of people were run down rather than waved off.
The first was the flashlight. A resident who watched the fire begin told investigators that approximately fifteen minutes after first seeing it, he saw a person walking on the trail in the wash with a flashlight. He was asked directly about transient or homeless activity around the canyon where the fire came from and dismissed the idea, noting he sometimes sees people experiencing homelessness at a bridge further west of the wash. The elimination section records the outcome: a report of a person with a flashlight leaving the Eaton Wash area at the time of the fire was investigated and did not yield any information, and the location the person was seen was more than half a mile from the origin area. Half a mile of steep, unlit, roadless terrain in an eighty mile per hour wind, in the fifteen minutes after ignition, is not a route anyone walks away by.
The second came through official channels. On January 13, 2025, CAL FIRE Deputy Chief Tim Rogers notified the team that a report existed of a fire in Eaton Canyon involving the California Highway Patrol and an alleged suspect leaving the area. The team contacted the CHP Southern Division Communication Center, obtained the call logs and audio, and spoke to the officers and their supervisor. The conclusion: no subject was seen leaving the area, the location was a smouldering patch of brush along the fire's perimeter, and there was no evidence on the scene to indicate an intentionally set fire.
What remained
With lightning, campfire and arson eliminated, electrical lines remained, and the affirmative evidence for that hypothesis was already substantial: two arc flashes on video at the moment of ignition, glowing material falling, ignition twelve seconds later, converging fire indicators encompassing the bases of the towers, beaded metallic material recovered from Tower #3, and a large body of witnesses independently describing a ring of fire at the base of the towers.
The initial report's opinion section states the conclusion as electrical in nature, caused by an electrical event at approximately 1811 hours within a grouping of three SCE transmission towers. The supplemental report, after the laboratory work, names the component.
One point of honesty about the site's own record: our fire database has carried a field for officially determined arson since it was built, and for the Eaton Fire it read "No, not determined" throughout the eighteen months when no determination existed. It now reads the same, for a different and much stronger reason. Arson was considered by name and excluded on evidence.