(This story was updated with more information from fire officials and to finalize containment figures.)
Fire crews responded to a brush fire Monday night near Auto Center Drive in Ventura.
The blaze was reported around 6:50 p.m. in the Santa Clara River bottom, in an area between Ventura and Oxnard, as Santa Ana winds whipped through the region.
Auto Fire was ultimately mapped at 61 acres and as of Friday afternoon it was 100% contained, according to Andrew Dowd, a firefighter and spokesperson for the Ventura County Fire Department.
The cause remains under investigation, Dowd said Friday.
Forward progress on the fire had been stopped shortly before midnight Monday.
Because of the fire's location within the river bottom, it never threatened any structures, Dowd said.
An evacuation order was issued around 9:30 p.m. Monday, however, for the Santa Clara River between the 101 Freeway and Victoria Avenue. No residential structures were evacuated.
Homeless encampments dot the riverbed, and some commercial businesses surround the area where the fire erupted.
Firefighters remained on scene overnight to work on brush and thick and heavy grass called arundo.
"Because of the size, it will be a long night of hard work to get the heat out of certain portions of this fire," Dowd said Monday night.
Within an hour of the fire's start, the fire was pegged at 5 acres, according to initial fire reports. Ground crews and helicopters quickly rushed to the area, making water drops.
At one point early on, the fire had reached into River Ridge Golf Club across the river in Oxnard. Radio traffic indicated the course superintendent planned to put on the sprinklers.
More air support had been requested, and by 9 p.m. a helicopter from Los Angeles County appeared to be on its way, according to radio traffic.
Traffic along Victoria Avenue, which runs through both Ventura and Oxnard, was shut down between Gonzales Road and Olivas Park Drive as onlookers snarled traffic and made access more difficult.
By 9:30 p.m. Monday, an estimated 100 firefighters were battling the blaze, which had grown to about 10 acres.
A second fire in Simi Valley was reported at 7:48 p.m. Monday. The Royal Fire ignited in the central part of the city near Darrah Volunteer Park and the Arroyo Simi Equestrian Center, according to initial fire reports. It was soon stopped at about an acre.
The fires broke out as much of Ventura County was on the eve of the most extreme fire weather conditions categorized by the National Weather Service: a "particularly dangerous situation," or PDS, red flag warning. The PDS red flag warning, which started at 4 a.m. Tuesday, was scheduled to last until noon Wednesday.
The designation, first used in 2020, has been issued only a few times prior, including when the Mountain Fire broke out in Somis and the hills above Camarillo on Nov. 6, when the Franklin Fire started near Malibu on Dec. 9 and on Jan. 7 and 8, when the Palisades and Eaton fires erupted in Los Angeles County.