The Thomas Fire was a massive wildfire that affected Ventura and Santa Barbara counties, and one of multiple wildfires that ignited in Southern California in December 2017. It burned approximately before being fully contained on January 12, 2018, making it the largest wildfire in modern California history at the time. It was surpassed by the Ranch Fire, part of the Mendocino Complex, in August 2018. The fire is currently the eighth-largest wildfire in modern California history, as of 2025. The fire was officially declared out on June 1, 2018, after more than two months in which no hotspots were detected. The Thomas Fire destroyed at least 1,063 structures, while damaging 280 others; and the fire caused over $2.2 billion (2018 USD) in damages, including $230 million in suppression costs, entering the 10 most destructive wildfires in state history at the time. , the Thomas Fire is California's 17th-most destructive wildfire. Ventura's agriculture industry suffered at least $171 million in losses due to the Thomas Fire.
By January 2, 2018, the Thomas Fire had cost over $204 million to fight, and had forced over 104,607 residents to At its height, the Thomas Fire saw over 8,500 firefighters mobilized to fight it, which is the largest mobilization of firefighters for combating any wildfire in California history.
The fire began on December 4, north of Santa Paula, near Steckel Park and south of Thomas Aquinas College from which the fire was named. Though the fire started near the college, no buildings at the college were burned in the fire. The fire quickly reached the city of Ventura, where over five hundred residences were destroyed that night. The fire destroyed almost as many residences in several rural communities amidst the rugged mountain terrain of Ventura County. The fire threatened the Ojai Valley, and on December 13, the fire completely surrounded the area, including Lake Casitas. The fire began burning through the rugged Santa Ynez Mountains as it threatened several small communities along the Rincon Coast north of Ventura, expanded into the Los Padres National Forest, and reached Santa Barbara County. Firefighters concentrated on protecting the communities of Carpinteria and Montecito in the southern portion of the county as the fire burned in the foothills of the Santa Ynez Mountains where access was difficult.
The unusually strong and persistent Santa Ana winds were the largest factor in the spread of the fire. Much of Southern California experienced "the strongest and longest duration Santa Ana wind event we have seen so far this season", according to the National Weather Service. The region experienced an on-and-off Santa Ana wind event for a little over two weeks, which contributed to the Thomas Fire's persistent growths in size. At its height, the wildfire was powerful enough to generate its own weather, qualifying it as a firestorm. There were periods of time when the fire was advancing at a rate of an acre (0.4 ha) per second. The winds also dried out the air, resulting in extremely low humidity. The area, along with most of Southern California, experienced the driest March-through-December period on record.
While November is the typical beginning of the rainy season in California, the first measurable rain for the area fell on January 8, 2018, more than a month into the fire. With the natural vegetation burnt, flash floods and mudflows damaged homes in Montecito when the rains arrived. Evacuations were ordered or anticipated for neighborhoods that sit below areas recently burned by the Thomas Fire and other wildfires. By January 10, at least 21 people had been killed by the sudden flooding and debris flows that followed the heavy rains, which also destroyed over 100 homes.
Progression
December 2017 On December 4, 2017, the fire was first reported by a nearby resident at 6:26 p.m. PST, to the north of Santa Paula, near Steckel Park and Thomas Aquinas College, after which the fire is named. That night, the small brush fire exploded in size and raced through the rugged mountain terrain that lies west of Santa Paula, between Ventura and Ojai. Officials blamed strong Santa Ana winds that gusted up to for the sudden expansion. Soon after the fire had started, a second blaze was ignited nearly 30 minutes later, about to the north in Upper Ojai at the top of Koenigstein Road. According to eyewitnesses, this second fire was sparked by an explosion in the power line over the area. The second fire was rapidly expanded by the strong Santa Ana winds, and soon merged into the Thomas Fire later that night. According to statements released by investigators on March 13, 2019, Southern California Edison was responsible for both ignitions.
Late on the night of December 4, the Thomas Fire reached the hillside neighborhoods of Clearpoint, Ondulando, and Skyline in the city of Ventura and destroyed many single-family detached homes. Many people fled with little or no warning when evacuation orders were issued, as the fire had traveled in just a few hours.
Tuesday morning, on December 5, saw 1,000 firefighters battling the blaze, with no containment of the fire. At 7 a.m. PST, one helicopter began dropping water, while fixed-wing aircraft waited to be deployed after the winds died down. The firefighters tried to save Ventura homes in the midst of a red-flag wind advisory with ridgeline winds of and gusts up to . The fire continued jumping across the valleys along the steep slopes of the foothills that abut the northern portion of the city. As the fire traveled along the interface between the foothill rangeland and the area developed with homes, it reached the hills above downtown where several apartment buildings and other homes above downtown Ventura were damaged or completely destroyed. The fire burned over Grant Park above City Hall, and burned along the ridge above the western portion of the city, which stretches north along the narrow Ventura River valley, and is characterized by steeply-sloped sides.
The fire continued moving north up the valley throughout the day. The entire community of Casitas Springs, which lies northwest of Ventura, had a mandatory evacuation issued as the fire approached. The fire reached Black Mountain overlooking Ojai. The entire Ojai Valley was given mandatory or voluntary evacuation orders. The Ojai pumping system was damaged by the fire and the entire water system stopped working for a time so water was not available from the hydrants for use by the firefighters. The western flank of the fire jumped over Highway 33 and burned through the Taylor Ranch oil fields on the other side of the valley. The fast-moving, wind-driven wildfire continued past the area that had burned in the 2015 Christmas Day Solimar Fire, before crossing the 101 Freeway to the Solimar Beach area, on Pacific Coast Highway, along the Pacific Ocean. The fire continued its northwesterly march along the Rincon Coast to Rincon Point, at the Santa Barbara County/Ventura County line.
On Tuesday, December 5, additional National Guard helicopters were brought in to fight the six largest wildfires burning in Southern California. Officials said they also obtained "every last plane we could find in the nation." C-130 airplanes were obtained from the U.S. military, and more than 290 fire engines came from Montana, Utah, New Mexico, Idaho, Arizona, Oregon, and Nevada.
On December 7, the Thomas Fire grew further to , with containment of the fire at 5%. On December 8, the Thomas Fire grew to with containment of the wildfire increasing to 10%, after the Santa Ana winds died down.
On December 9, as the Santa Ana winds returned, the Thomas Fire expanded to , while containment of the fire increased to 15%. By the afternoon of the same day, the fire entered Santa Barbara County near Divide Peak.
Early on December 10, the Thomas fire expanded to , but containment of the blaze stayed the same as the previous date, at 15% total containment. The evacuation orders were expanded further north into Santa Barbara County into the communities of Carpinteria and Montecito. Only the southern and southeastern flanks of the wildfire had been contained. However, by the evening of the same day, the powerful Santa Ana winds had caused the Thomas Fire to undergo another period of explosive growth, expanding to in size, with containment dropping to 10% overall, indicating no new progress in fire containment. Another firefighter was injured, when he fractured his leg, and he returned home to recover.
On the same day, fire analysts stated that the Thomas Fire had been generating its own weather for the past two days, a behavior only observed in very massive wildfires and indicative of a firestorm. The Thomas Fire was generating massive pyrocumulus clouds, which were gathering heat from the flames below, although the unstable column of air could collapse at any time, which would generate sudden wind shifts near the fire and pose a major hazard to firefighters. This behavior had been previously observed during the massive 2009 Station Fire in Los Angeles. At this point, the Thomas Fire had become the fifth-largest wildfire in modern California history and the largest wildfire recorded in California in December. The Thomas Fire was also estimated to be at least the 10th most destructive wildfire on record in California.
On the morning of December 11, the Thomas Fire had grown to , while containment of the fire had increased to 15%. After this expansion in size, the Thomas Fire's northwestern flank almost linked up with its southwestern flank, to the east of Carpinteria, cutting across parts of Route 150, and threatening to envelop Ojai and Lake Casitas. By this time, the Thomas Fire had grossly surpassed the size of the previous largest fire in December, which was extremely unusual. Fire officials noted that many areas had been "Moonscaped", an event in which the brush has been so completely burned that it was left looking like a barren and blackened landscape, resembling the surface of the Moon, which is indicative of extreme fire behavior. During the evening of December 11, the Thomas Fire expanded further to , while firefighters increased containment of the fire to 20%.
On December 13, the Thomas Fire's expansion slowed on its west flank, as it reached the burn area of the from 2007. However, the Thomas Fire's northwestern and southwestern flanks merged on the western shore of Lake Casitas, completely encircling the lake and the Ojai area. Firefighters have expected the fire's growth to be disrupted if it reaches the burn scars of other previous fires to the west within the last 10 years: the Tea, Jesusita, Gap, and Rey Fires.
On December 14, the Thomas Fire expanded further to , surpassing the Zaca Fire to become the fourth-largest wildfire in modern California history. Later on the same day, the Thomas Fire expanded further to . On the same day, a Cal Fire Engineer (Cory David Iverson) died, while working northwest of Fillmore, on a flareup near the eastern flank of the fire.
On the morning of December 15, containment lines in the Santa Barbara and Montecito areas and protecting nearby homes was the priority, in addition to the threatened Carpinteria and Summerland areas. Officials feared the sundowner winds could push the fire into those communities as they blow south from the mountains down to the coast, and because they also dry out the air. Although they prevented the fire from reaching the community, it still grew to with 40% containment on the morning of December 16, surpassing the Rim Fire in size, and becoming the third-largest wildfire in the modern history of California. Around this time, officials and experts feared that the Thomas Fire could surpass the Santiago Canyon Fire of 1889, which had burned over , and is believed to be California's all-time largest wildfire on record.