Some 20,000 people are impacted by 566 fires burning in the region.
Forrest Clark, 51, of Trabuco Canyon, California, is being held in lieu of $1 million bail for allegedly starting the Holy Fire ravaging Trabuco Canyon, California. He faces life in prison if convicted, The National Forest Service said.
Air quality worsened in states as far away as Utah, as smoke from California's 17 wildfires released pollutants into the atmosphere where they can remain for weeks.
"The more serious predictions of warming and fires to occur later in the century, 2040 or 2050, they're now occurring in real time," the governor said.
It's expected that the fire will continue to spread to the south and east.
The blaze has destroyed about 500 homes, businesses and other structures.
"This fire is extremely dangerous, and moving with no regard for what's in its path."
Some 178 firefighters from 32 agencies are tackling the blaze.
Photos posted on social media showed significant smoke rising from the hills above residential areas.
Colorado's governor has called for an investigation into the bullets that allegedly caused the fire.
The Grant Fire was first reported around 5.30 p.m. in Alameda County.
"[The Klamathon Fire has] destroyed structures, threatened homes and critical infrastructure and caused the evacuation of residents," said California Governor Edmund G. Brown.
In the days after the fire, residents rummaged through the debris, searching for salvageable belongings amid the destruction.
The fire is one of four that broke out on Wednesday and continued to grow, but no evacuations have been ordered so far.