The so-called Valley fire is thought to be one of the worst in the state's history, and is still only 30% contained, spanning three counties.
One disabled woman has died and four firefighters have been injured, while 23,000 people have been forced to flee their homes.
Two dozen fires are raging in Oregon, California and Washington state.
But the most destruction is in California, where mandatory evacuation orders have been lifted in some areas so residents can return to survey the devastation.
Firefighters are scrambling to protect not only homes but the state's famed giant Sequoia trees, as the largest of a dozen fires edges ever closer to one of the national parks in which they grow.
While the Valley fire has been the most destructive, covering an area twice the size of San Francisco, a second known as the Butte fire, outside Sacramento, has claimed 166 homes.
Firefighters say it is covering 71,780 acres (29,048 hectares) and is now 40% contained.
Officials say fire teams have been helped by cooler weather and higher humidity, although the forecast is for higher temperatures to return at the weekend
In California, the sound of summer is the crackle of flames. No one here in Lake County can remember anything like the Valley Fire.
Firefighters say it has already consumed an area twice the size of San Francisco. And still it burns, leaving behind a landscape drained of colour, silent and lifeless.
Ranches which stood here for more than a century were wiped out in seconds. And in the little communities of Cobb, Middletown and Hidden Valley, entire streets have been destroyed.
For mile after mile the ashes are still smouldering. Most people have not yet been allowed to return to inspect the damage but when they do many will find that there is nothing to salvage.
Cooler weather with some moisture in the air is helping but it will take more than that to stop the blaze. The fires burns and burns and California is counting the cost.
In northern California, people who have been evacuated from their homes or lost their homes completely are gathered at emergency centres and high schools.
Andy Elliott, a British firefighter working to battle the Valley fire, said it is one of the most extreme in California for a long time.
Firefighters are calling it a "career fire", such is its speed and force, he said. "The fire behaviour is unprecedented."
Mr Elliot said he knew the four injured firefighters and had breakfast with them just before they were hurt.
"It's a very extreme incident... very sad."
California is used to battling raging wildfires. But after a four-year drought, the state is suffering more than usual - 5,255 fires have scorched 217,827 acres of land so far this year, compared with 3,638 fires burning 90,894 acres during the same period last year.
Northern California is currently bearing the brunt of the blazes, with 13,000 firefighters working 24-hour shifts to try to contain more than a dozen fires sweeping across parched hillsides in Butte, Lake, Napa and Sonoma counties.
But Calfire's Lynnette Round says more wildfires could start anywhere in the state at any given moment. "The terrain is so dried up that even if it rains a little, trees and brush are so dry, they could ignite at any time," she says.
Southern California typically experiences its worst wildfires in October and November, when ferocious Santa Ana winds - which blow from the desert to the coast - can reach up to 80mph and whip blazes across swathes of arid land.
The state's largest wildfire in recent years was in San Diego county in 2003. That burned 273,246 acres, 2,820 buildings and led to 15 deaths.
California's deadliest wildfire on record was also in southern California, according to Calfire. Twenty-nine people died in Los Angeles county in 1933.
Analysis by Vanessa Barford, BBC News in Los Angeles
A blazing wildfire in northern California has grown to 104 square miles, with nearly 600 homes destroyed.