The so-called “Blue Cut Fire” erupted on Tuesday in the mountainous Cajon Pass northeast of Los Angeles.
Named for a narrow gorge in the area, it had charred some 34,500 acres (nearly 14,000 hectares) by early yesterday.
The fast moving fire grew nearly 10,000 acres (4,000 hectares) overnight, fire officials said.
Firefighters impeded by treacherous terrain and the intensity of the fire have so far managed to carve containment lines around only 4% of it, officials said on the InciWeb tracking website.
Forest and brush dried by severe drought were helping to feed the flames.
Fire officials, who have described the fire’s intensity as highly unusual, expressed concern that weather conditions would keep the area dry, hot and windy.
Temperatures are expected to hover around 90° Fahrenheit (32° Celsius), according to the National Weather Service.
Much of the fire is burning in uninhabited areas between the San Bernardino and San Gabriel mountains, but populated areas are being affected.
About 80,000 residents have been ordered to evacuate including the community of Wrightwood, about 60 miles northeast of Los Angeles.
It was not immediately clear how many residences had burned.
Gowever, San Bernardino County Fire Department spokesman Louis Penna said in an e-mail that at least dozens of structures had been destroyed.
A number of school districts and a hospital clinic, all of which were closed yesterday, were being threatened by the blaze, according to InciWeb.
Transportation officials said a northbound stretch of Interstate 15 that was closed earlier in the week would reopen by the end of the day.
The highway runs between Los Angeles and Las Vegas.
The fire was directly burning through and under a high voltage transmission line and it was within a quarter mile of two other lines.
Electric operators have asked utility companies not to take lines or power plants out of service for maintenance to avoid overburdening California’s electric grid.
There was no immediate concern about widespread outages, California Independent System Operator spokesman Steven Greenlee said in a telephone interview.
The blaze is the latest wildfire in the US West, where years of drought have put a heavy burden on firefighting resources.
Plumes of smoke from the Blue Cut Fire could been seen from space in images captured on Wednesday by a Nasa satellite, according to the Jet Propulsion Laboratory.
The cause of the fire is under investigation.