LOS ANGELES (Reuters) - A wildfire in a forest north of Los Angeles that forced thousands of holiday campers to flee the fast-moving flames was ignited by candles used in an animal sacrifice ritual, fire officials said on Thursday.

U.S. Forest Service investigators initially believed that lightning started the 17,000-acre (6,880 hectare) Curve Fire, which started on Sunday in a bend of a highway that wends through the Angeles National Forest.

But after inspecting the point of origin, clues emerged that human activity was involved, said Rich Phelps, a fire information officer.

"The Curve Fire investigation team has concluded candles associated with a ritual involving the use of fire and animal sacrifices started the fire," Phelps said.

The Angeles National Forest, home to the San Gabriel Mountains, has long been a popular site for practitioners of Santeria, a Westernized form of African deity worship.

Santeria rituals commonly include the sacrifice of goats, chickens and other small animals, and take place in a forest, which is considered a sacred place akin to a house of worship, experts said.

Law enforcement officers routinely find tableaus of dead animals, votive candles and shredded clothing in secluded spots throughout the Angeles National Forest, said Deputy David Smail.

Deputies rarely see the rituals in progress but about once a month they find leftovers that are not carried off by animals, Smail said.

"They go off into the woods and do their little thing," Smail said. "It's hard (to catch them) because they sometimes have lookouts."

No other information was made public about the items found at the Curve Fire site, nor had investigators identified suspects in the case.

The Curve fire erupted at about noon on Sunday as thousands of campers enjoyed the final weekend of summer vacation in the 650,000-acre (263,000-hectare) national park.

Gusty winds combined with record heat and drought conditions to propel the fire up the rugged slopes, driving more than 7,000 campers out of their sites within hours.

By Thursday, the fire had consumed more than 17,000 acres and destroyed 72 structures, including three forest service buildings and about 50 vacation cabins, Phelps said.

It threatened to sever one of the major arteries of the state's power grid, which could have cut off power to some commercial consumers in Southern California.