First reported on July 27, 2018, both fires burned a combined total of 459,123 acres (1,858 km2), before they were collectively 100% contained on September 18,[1] though hotspots persisted until the complex was fully brought under control on January 4, 2019.

[6][7] The city of Lakeport, communities of Kelseyville, Lucerne, Upper Lake, Nice, Saratoga Springs, Witter Springs, Potter Valley, and Finley, parts of Hopland, and the tribal communities of Hopland Rancheria, Big Valley Rancheria, and Habematolel Pomo of Upper Lake were evacuated.

[14] The Ranch Fire finally reached full containment during the evening of September 18.

[1] The Mendocino Complex comprised two vegetation fires that burned within miles of each other near Clear Lake, in Northern California.

By the evening, the River Fire had burned 4,000 acres (16 km2) and destroyed two buildings, including a home.

[18] According to a 2019 report, the Ranch Fire was started by a rancher who had inadvertently sparked dry grass while hammering a metal stake while trying to find a wasp nest.

[8][19] The fire threatened the University of California Hopland Research and Extension Center.

[18] High heat, low humidity, and rugged terrain challenged control of the fires, with gusty winds causing both to grow.

With Red Flag Warnings in effect, the first mandatory evacuations began in Hopland and with residents along Highway 175.

Dry and windy conditions persisted, and the lack of available firefighters due to other fires burning in the state slowed attempts at containment.

By the morning of August 2, the two fires had burned a combined total of 110,168 acres (446 km2) and were 39 percent contained.

By Wednesday morning, on August 8, 2018, the Mendocino Complex Fire had burned 300,086 acres (1,214 km2) and was 47% contained.

By Saturday morning, on August 11, 2018, the Mendocino Complex Fire had burned 325,226 acres (1,316 km2), was 67% contained, and had destroyed 258 buildings.

[43][44] August 19 was a day of chaos wherein LAFD firefighters were surrounded and had to scramble through the forest to safety.

On November 7, 2018, InciWeb stopped issuing updates on the Mendocino Complex and declared the incident to be inactive.

[3] The River and Ranch Fires impacted communities along the Mendocino and Lake County borders, prompting the evacuations of Lakeport, Kelseyville, Lucerne, Upper Lake, Nice, Saratoga Springs, Witter Springs, Potter Valley, Finley, parts of Hopland, and the tribal communities of Hopland Rancheria and Big Valley Rancheria.