The fire was started by lightning strikes east of Loyalton along the eastern edge of the Sierra Valley, near Mount Ina Coolbrith on the Tahoe National Forest.

The National Weather Service issued its first-ever fire tornado warning resulting from the building pyrocumulonimbus cloud in response to the incident, which went into effect for Lassen County.

[7] Crews had made progress on the southeast flank of the fire on August 17, mandatory evacuations were lifted for Cold Springs, and SR 70 was reopened.

[9] By evening, advisory evacuation orders were in place for Loyalton, Chilcoot, Vinton, and Sierra Brooks.

[11] On August 18, the fire had been largely contained in the north and east, and mandatory evacuations were lifted in Lassen County.

However, it continued spreading rapidly to the south and west, largely due to the lightning strikes there the previous day.

Air quality continued to be extremely poor in Sierra Valley and Reno, with visibility highly impaired by smoke.

All evacuation orders were lifted as of this time, though the Dog Valley area of the Humboldt-Toiyabe National Forest remained closed.