Rancho Cucamonga, Calif. ? With ash and smoke turning day into night, a wind-driven wildfire closed in Friday on several Southern California communities east of Los Angeles, destroying four houses and forcing firefighters to make their stand in back yards.

Thousands of people were evacuated and two major freeways were closed for a time.

“We got out what was important, and what’s most important is us,” said Christiane Elin, 30, who with her husband was among hundreds of people gathered at a high school serving as an evacuation center in Rancho Cucamonga.

About 12,600 acres have burned since the fire started Tuesday in the hilly residential areas near the San Bernardino National Forest.

For the week, about 20,000 acres have been scorched by several fires across Southern California.

Ash covered cars a half-mile from the fire in San Bernardino County, and billowing clouds of black smoke hung above the heavily developed area. The California Highway Patrol temporarily closed Interstate 210 and Interstate 15, the main route to Las Vegas.

“It looks like nighttime here,” said Kelly Bocanegra, an elementary school teacher.

Firefighters supported by water-dropping aircraft battled flames in back yards in Rancho Cucamonga. The fire also reached the outskirts of Fontana and Rialto in the sprawling suburbs about 50 miles east of downtown Los Angeles.

The flames were fanned by hot, dry desert winds of 25 mph and higher, and temperatures reached into the 90s. The fire was only 17 percent contained.

Firefighters watch as flames near an area of new homes in Rancho Cucamonga, Calif. Flames pushed by hot Santa Ana winds jumped ridges and roads Friday in the area, forcing the evacuation of thousands of residents.

Forecasters said the wind would only get stronger — with sustained winds of up to 35 mph today and up to 40 mph Sunday, with higher gusts.

Gov. Gray Davis ordered all available firefighting resources to be made available.

About 30 miles west of the fire, a light dusting of ash fell on Santa Anita racetrack in Arcadia, the site of today’s $14 million Breeders’ Cup World Thoroughbred Championships.

Horses worked out under a hazy sun as a huge plume of smoke hung in the distance.

“I hope it doesn’t blow this way because the air quality would certainly be a concern,” trainer D. Wayne Lukas said.

The fire, which authorities blamed on arson, was one of several that swept the region this week.

At Camp Pendleton Marine Corps Base, 50 miles north of San Diego, a 4,110-acre brush fire was as close as a mile from scattered ranches and homes.