Firefighters have struggled against rugged terrain, high winds and an August heat wave to slow the spread of the biggest wildfire ever recorded in California, an inferno that exploded to be nearly the size of Los Angeles in just 11 days.
The blaze, centred near the community of Upper Lake, about 160km north of San Francisco, spread fast because of what officials said was a perfect combination of weather, topography and abundant vegetation turned into highly flammable fuel by years of drought.
Firefighting efforts were also initially hampered by stretched resources, the Department of Forestry and Fire Protection, also known as Cal Fire, said.
When the fire started July 27, thousands of firefighters were hundreds of kilometres north battling a massive blaze that spread into the city of Redding, destroying more than 1000 homes, in addition to a dozen other major blazes.
The flames were raging in mostly remote areas, and no deaths or serious injuries were reported. But at least 75 homes have been lost, and thousands of people have been forced to flee. The blaze, dubbed the Mendocino Complex, was reported 20 per cent contained on Tuesday.
Its rapid growth at the same time firefighters were battling more than a dozen other major blazes around the state fanned fears that 2018 could become the worst wildfire season in California history.
About 3900 firefighters, including crew from Australia and New Zealand, were battling the blaze, contending with temperatures in the high 30s celsius and winds gusting to 40 km/h.
The heavily-forested area of myriad canyons where the fire is spreading has few roads or natural barriers that can serve as firebreaks or offer safe havens for firefighters to battle the flames head on.
So firefighters instead fell back to natural barriers like streams or used bulldozers to cut fire lines.
But the flames were moving so fast in spots that they blew past fire lines, forcing firefighters to retreat
In all, 14,000 firefighters were battling blazes across California, which is seeing earlier, longer and more destructive wildfire seasons because of drought, warmer weather attributed to climate change, and the building of homes deeper into the forests.
In becoming the biggest fire in California history, the Mendocino Complex fire broke a record set just eight months ago. A blaze in Southern California in December killed two people, burned 1140 square kilometres and destroyed more than 1000 buildings.
