(Reuters) – A portion of a major highway connecting Los Angeles and Las Vegas has been reopened, as a wildfire that forced the evacuation of some 80,000 Southern California residents continued to rage virtually unchecked.

The so-called Blue Cut Fire erupted on Tuesday in the mountainous Cajon Pass northeast of Los Angeles and, by late Wednesday night, had exploded to cover 25,626 acres (10,370 hectares), fire officials said.

While firefighters had managed to carve containment lines around only 4 percent of the blaze, state transit officials said northbound lanes of Interstate 15 would reopen in the area.

Fire officials expressed concern that “red flag” weather conditions would keep the area dry, hot and windy into Thursday night.

The Blue Cut Fire, named for a narrow gorge north of San Bernardino where it started, threatened the town of Wrightwood near a ski resort and other communities, prompting evacuation orders for some 80,000 residents.

Authorities have described the blaze as unusually fierce, even for a year of intense wildfires in the U.S. West, where years of drought have placed a heavy burden on firefighting resources. The cause of the fire was under investigation.

U.S. government forecasters have said the risk of major wildfires in Southern California is likely to remain high until December, given the dryness and warm weather.

About 600 miles (970 km) to the northwest, the so-called Clayton Fire was 50 percent contained after charring nearly 4,000 acres in and around the community of Lower Lake and destroying 286 homes and other structures, according to the California Department of Forestry and Fire Protection.

(Reporting by Curtis Skinner in San Francisco; Editing by Kevin Liffey)