The wildfire, which began on Tuesday in Southern California’s Cajon Pass, has so far spread to 18,000 acres and chased 82,000 residents from their homes in less than 12 hours.
“It is a very fast-moving fire, it has wind behind it,” said US Forest Service spokeswoman Lyn Sieliet.
The Blue Cut fire, fed by strong winds, bone-dry brush and 100-degree temperatures, has scorched hills, canyons and flatlands.
“We know that we’ve lost structures, it’s unknown how many at this time,” said San Bernardino County Fire Department public information officer Tracey Martinez. “This fire is still raging out of control.”
The fire “is burning in significantly different terrains at multiple elevation levels,” making it difficult to fight it, said Eric Sherwin of the San Bernardino County Fire Department.
Another fire began Saturday in the foothill community of Lower Lake some 130 kilometers (80 miles) north of San Francisco.
The blaze, which has been fueled by fierce winds, had burnt about 4,000 acres (1,600 hectares) by late Monday afternoon.
Damin Pashilk, 40, was arrested on Monday and faces 17 counts of arson over the destructive Clayton Fire, which is one of a dozen major wildfires across the drought-hit US West.
California is undergoing its fifth year of a record drought and is being hit by an extreme heat wave.