The sprawling Mendocino Complex fire in Lake County, which became the largest in state history earlier this week, had grown to 304,402 acres as of Thursday morning, officials said. He also faces sentencing enhancements for arson of multiple structures.
Two firefighters were treated for heat-related injuries Monday.
He said they were still working through the evidence to determine how it was started.
Volunteer Fire Chief Mike Milligan told the Orange County Register that Clark was screaming in the community and sent an email that said "this place will burn" last week. "We continue to actively engage, but can not get ahead of the fire", it said.
Thursday afternoon and evening the Holy Fire northwest of Lake Elsinore in Southern California bumped up against homes on the southeast and east sides of the fire. "I reported this over and over again".
U.S. Homeland Security Secretary Kirstjen Nielsen asked residents to prepare for future emergencies and thanked firefighters and other personnel battling California's deadliest wildfire this year.
Los Angeles' CBSLA reported that 51-year-old Forrest Gordon Clark initially refused to leave his jail cell to appear before his judge.
Before his arrest, Clark told a freelance cameraman he was asleep when the fire started and had no idea how it began.
The call for voluntary evacuations was issued Thursday for people near a mountainside above Lake Elsinore, joining at least 20,000 people who are under mandatory evacuation orders as fire churns through Cleveland National Forest. He also claimed he had been threatened by the MS-13 gang.More news: DOOM Eternal Is Coming To Nintendo Switch
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Wildfires across California and the region could be further stoked by strong gusts, low humidity and hot weather on Friday and Saturday, forecasters warned.
Orange County sheriff's deputies received a call reporting "erratic behavior" by Clark on July 23 and placed him on a psychiatric hold, the Associated Press reported, citing Carrie Braun, a department spokeswoman.
Eric Lint, a neighbor of Clark whose cabin burned in the blaze, said he was not surprised by Clark's arrest.
Clark spoke to a stringer photographer with OnScene outside his cabin, insisting he had nothing to do with the fire.
The fires all grew explosively in the past two weeks as winds whipped the flames through forest and rural areas full of timber and brush that is bone-dry from years of drought and a summer of record-breaking heat.
Orange County Supervisor Todd Spitzer didn't mince words at a news conference Wednesday.
It was 49 percent contained with firefighters struggling in steep terrain to control the blaze, CalFire said.
Although it's not the largest fire burning in the state, there are growing concerns about how it could affect residential communities, including Lake Elsinore.