AZUSA, Calif. -- A wildfire spread rapidly across 10,000 acres of national forest, sending thousands of holiday campers fleeing.

About 8,000 campers, hikers and residents had to leave the Angeles National Forest after the fire erupted Sunday afternoon. Several said they were separated from friends and family and had to leave their belongings behind.

"They told us we had 10 seconds to get out, to run," Lisette Cardenas told a Los Angeles television station. "You could see the smoke right behind us."

The fire rapidly spread north on both sides of Highway 39 north of Azusa, about 30 miles east of downtown Los Angeles, said U.S. Forest Service spokeswoman Gail Wright.

Authorities said possible causes included a lightning strike and a propane tank explosion. The fire destroyed an abandoned forest service building.

Farther north, in El Dorado County about 40 miles east of Sacramento, another fire destroyed one house, consumed 776 acres and was threatening 30 other homes.

A 15-year-old boy was being detained Monday in connection with the fire. A second boy, also 15, was released to his family on Saturday after being questioned by authorities, said sheriff's Lt. Kevin House.

House said at least one of the boys was playing with matches when the fire ignited Saturday amid heavily forested canyons between the cities of El Dorado Hills and Rescue. Forest Service spokesman Ken Thompson said firefighters hoped to have it contained by Tuesday.

In Wrightwood, about 55 miles northeast of Los Angeles, a 554-acre fire was 61 percent contained. Investigators had found a body in the fire and drug manufacturing equipment for a methamphetamine lab nearby, Forest Service spokeswoman Karen McKinley said.

Nationwide, the National Interagency Fire Center reported 18 large active fires Monday that had burned more than 667,000 acres in eight western states.