It ignited on July 24, 2024 in an alleged act of arson in the city of Chico's Bidwell Park in Butte County.

Thousands of people in foothill communities evacuated, Lassen Volcanic National Park closed to the public, and hundreds of buildings were destroyed.

The brisk expansion of the Park Fire in late July was driven in large part by antecedent hot and dry conditions.

[1][2][3] July of 2024 was California's hottest month ever recorded, stoked by a heatwave almost two weeks in duration focused on the interior of the state.

[5] Evaporative demand (a measure of the atmosphere's capability to draw water out of vegetation and other sources of moisture) increased across much of the state, and particularly so in the Central Valley.

[2] The topography of the county ranges from the flat Central Valley in the west to the forested Sierra Nevada in the east, with grasslands, oak woodlands, and chaparral landscapes in between.

[10][11] Shortly before 3:00 p.m. PDT on Wednesday, July 24, Chico resident Ronnie Dean Stout II, 42, driving his mother's 2007 Toyota Yaris, pulled it over to the side of a road in the Upper Park and went over a berm.

Eyewitness accounts assert that Stout instead put it in neutral and then pushed the burning vehicle backwards off the embankment, whereupon it fell approximately 60 feet (18 m) and landed in a ravine.

[14] Stout was arrested by Butte County District Attorney's Office and Cal Fire investigators at his residence in a Chico mobile home park at 1:30 a.m. the following morning.

At around 8:00 p.m., a convoy of 100–150 people eventually made their way out to California State Route 32 via logging roads when Sierra Pacific Industries (SPI), which owns much of the land surrounding the town, unlocked gates on their property.

[21] As it spread north, the fire established itself in the Ishi Wilderness, an area with little history of wildfire, heavy vegetation cover, and few easy access routes for ground-based firefighting personnel.

[24] Despite the efforts of ground crews and three night-flying helicopters, the wind-driven fire continued to burn largely north—parallel to California State Route 99—and into Tehama County.

At 4:40 p.m., the Butte County Sheriff's Office issued voluntary evacuation warnings for northwestern portions of the city of Paradise, which had been devastated by the Camp Fire in 2018.

[29] The Park Fire surpassed 300,000 acres (120,000 ha) in burned area by the morning of Saturday, July 27, less than 72 hours after ignition.

[34] The National Weather Service office in Sacramento issued a 24-hour flash flood watch for the entirety of the Park Fire burn scar, warning of potential debris flows from scattered showers and thunderstorms on August 23–24.

On Saturday the 24th, firefighters observed no active flames and containment of the perimeter reached 71 percent by that night, one month to the day after the fire's ignition.

[9] On Sunday, July 26, California governor Gavin Newsom declared a state of emergency for areas affected in Butte and Tehama counties.

[48] The fire prompted evacuation orders for parts of Butte, Shasta and Tehama counties,[49] including residential areas near Chico and the city's airport.

[24] By the morning of Thursday, July 25, more than 4,000 people were subject to evacuation orders, including the entire community of Cohasset.

Firefighting operations can introduce fire retardant—which is toxic to fish—into waterways, and post-fire rains may wash sediment and debris into the water, causing algal blooms, suffocating fish, or blocking parts of the river.

[61] The Butte County District Attorney's office announced the arrest of Ronnie Dean Stout II (born January 10, 1982), a 42-year-old resident of Chico on July 25, the second day of the fire.

[66] He was arraigned on July 29 in Butte County Superior Court in Oroville, and charged with reckless arson with multiple enhancements.