Lucas Fire,
Potter Valley.

A dated record of fast first-day growth, evacuation escalation, difficult access and the large gap between the latest statewide index and an older dedicated incident snapshot.

Editorial review: 21 September 2026 · Version 1

Active index4,128 acresCAL FIRE statewide listing

Containment100%Index reviewed 21 Sep

CountiesLake + MendocinoPotter Valley area

CauseUnder investigationCAL FIRE Mendocino Unit

Latest reviewed snapshot

From active growth to containment.

CAL FIRE’s active-incidents index reviewed on 21 September lists the Lucas Fire at 4,128 acres and 100% containment. The fire began on 10 September near the Lake–Mendocino county line in the Potter Valley area.

Difficult access

CAL FIRE described the incident as burning in remote, steep terrain and requested additional aviation resources during its first day.

Cause state

The cause remains listed as under investigation in the reviewed official material.

Rapid escalation

A single day changed the scale of the incident.

The first-day public chronology shows how quickly early incident estimates can evolve when a remote fire becomes established.

10:50 AM≈10 acInitial response

2:39 PM40 acSteep terrain

4:06 PM400 acEvacuations expand

7:51 PM1,099 ac · 5%Evening update

8:31 PM1,099.4 acFIRIS mapping

Do not convert these snapshots directly into a spread-rate curve. Published acreage can change because of growth, better mapping or both.

Evolution of knowledge

The dedicated page lags the statewide index.

Official-source gap · reviewed 21 Sep 2026

Active-incidents index4,128 acres · 100%

Newer statewide summary reviewed on 21 September.

Dedicated incident page1,099 acres · 5%

Older incident-page snapshot last updated on 10 September.

The difference is too large to treat the older dedicated page as the current incident state. Tecnobosque therefore keeps the timestamp attached to each value rather than merging them into a false single snapshot.

Community impact

Evacuations expanded during the first operational period.

CAL FIRE’s 10 September updates document evacuation orders and warnings in Lake and Mendocino counties as fire activity increased.

Orders and warnings

The 9:33 PM update listed multiple evacuation-order zones in Lake County and warning zones across both Lake and Mendocino counties.

Structure defense

At 5:29 PM, CAL FIRE reported structures threatened at the head of the fire and units moving into place for structure defense.

Night aviation

At 4:40 PM, additional evacuations were issued and night-flying helicopters were ordered.

Power impact

CAL FIRE reported a PG&E shutoff along part of Elk Mountain Road during the incident’s first evening.

Historical, not live: these evacuation and utility details describe 10 September conditions. Use current county and CAL FIRE information for present-day decisions. Evacuation warning vs order explained →

Evidence discipline

What remains unknown.

A final technical cause finding.
The complete mapped-perimeter sequence between the 10 September incident page and the later 4,128-acre statewide index value.
The exact dates on which every evacuation order and warning was modified or lifted.
A reconciled explanation for why the dedicated page remained on the older snapshot.
A final post-incident assessment of suppression outcomes and community impacts.

Provenance

Sources and release.

CAL FIRE — active incidents index ↗Source for the 4,128-acre and 100%-containment statewide snapshot reviewed on 21 September.
CAL FIRE — Lucas Fire incident page ↗Primary source for first-day chronology, location, cause, evacuations and the older 1,099-acre / 5% snapshot.
CAL FIRE — 10 September, 9:33 PM update ↗Source for 1,099 acres, 5% containment and dated evacuation zones.
CAL FIRE — 10 September, 5:29 PM update ↗Source for the 400-acre snapshot and structure-defense context.

Version 1 · 21 September 2026: initial developing record with first-day growth, source lag, evacuation history and evidence gaps.