Igniting during hot, dry & windy conditions on September 2, 2022, amid a record-breaking heat wave that spanned much of the state, the Mill Fire moved rapidly to the north.

[citation needed] The fire began at approximately 12:49 p.m. PDT during a red flag warning near Woodridge Court and Woodridge Way igniting a large warehouse on the property of Roseburg Forest Products, a lumber mill north of the town of Weed, before quickly igniting the nearby vegetation and rapidly beginning to burn through homes in the nearby neighborhood of Lincoln Heights.

[5] By 2:50 p.m., the fireline had jumped Jackson Ranch Road, several miles north of the ignition point, and had begun burning into the community of Lake Shastina.

[5] Within several hours the fire perimeter had doubled to 2,580 acres with 0% containment, as a state of emergency was declared for Siskiyou County by Governor of California Gavin Newsom.

[10] The Roseburg Forest Products veneer mill where the fire broke out produced its own electricity in a cogeneration facility that used wood remnants to provide fuel.

On September 7, Roseburg issued a press release announcing that the company was investigating the possibility that the machine had failed to sufficiently cool the ash, allowing a fire to break out.