Firefighters Begin to Contain Growing Wildfire Northwest of L.A.

Firefighters in Southern California made significant progress on Friday toward containing a wildfire that began in Ventura County and had spread into Los Angeles County, leaving thousands of residents under orders to leave the area.

The blaze, called the Canyon fire, began early Thursday afternoon near Lake Piru, a reservoir about 60 miles northwest of downtown Los Angeles. The fire was initially reported to have burned 30 acres, but it expanded quickly and had burned about 5,300 acres as of Friday morning, according to the California Department of Forestry and Fire Protection, the state’s main firefighting agency.

By the morning, firefighters had been able to contain at least 25 percent of the fire as it continued to spread east in Los Angeles County, officials said. The Ventura and Los Angeles County Fire Departments were leading the effort to contain the fire as it burned into the night, with 400 personnel deployed.

In Hasley Canyon, an unincorporated area near Santa Clarita, Calif., the fire had destroyed at least two structures, a shed and a home, and left acres of hillside scorched and covered in ash. Firefighters were patrolling neighborhoods in trucks and golf carts, looking for potential hot spots as temperatures began to rise in the afternoon.

The Canyon fire began on a particularly hot day in Southern California. The warm weather was not expected to abate. High temperatures in the mid 90s to low 100s were forecast through the weekend in the area of the fire, as well as dry conditions that could help fuel the flames even more, according to the National Weather Service.

When the fire started on Thursday afternoon, light winds were blowing, with gusts up to 20 miles per hour. Similar breezy weather that’s typical in the summer was expected through the weekend. David Gomberg, a meteorologist with the Weather Service office in Oxnard, Calif., called the wind “nothing out of the ordinary.”

Mr. Gomberg said the warm weather was the result of a hot air mass spread over Southern California. It’s expected to remain in place into next week.

“The earliest we could start seeing temperatures cool off would be Wednesday,” he said.

The heat and dry air have left the vegetation parched and flammable, and Mr. Gomberg said the dry vegetation and hot air mass were creating the potential for what are known as “vertical smoke plumes.” As the fire heats up in the afternoon, the warm air and smoke rise, creating towering plumes of smoke. These plumes can collapse, causing a downward rush of air, ash and embers.

“The concern is that it can cause pretty erratic fire,” Mr. Gomberg said.

Nearly 17,000 residents were under evacuation orders or were being told to prepare to evacuate, based on a New York Times analysis of the evacuation zones and LandScan population data.

A part of Valencia, a neighborhood of Santa Clarita, was under an evacuation warning. Valencia is home to Six Flags Magic Mountain, but the amusement park was not under any evacuation warnings or orders. The theme park wasopen on Friday and operating as normal as guests rode roller coasters just miles away from the fire.

The city of Santa Clarita was cautioning residents to avoid the area near the fire.

The Red Cross opened an evacuation center at a gym in the College of the Canyons in Santa Clarita. On Friday morning the center sat empty, with many residents appearing to have found other places to stay.

The Canyon fire on Thursday started as several other fires were burning across Southern California. Northwest of the Canyon fire, in San Luis Obispo and Santa Barbara Counties, the Gifford fire has been burning for days. As of Friday, it had burned more than 99,000 acres and was 15 percent contained, according to the state fire agency.

Qasim Nauman contributed reporting.