Investigators are considering an array of possible ignition sources for the huge fires that have killed at least 10 people and destroyed thousands of homes and businesses in the Los Angeles area. In hilly, upscale Pacific Palisades, home to Hollywood stars like Jamie Lee Curtis and Billy Crystal who lost houses in the fire, officials have placed the origin of the wind-whipped blaze behind a home on Piedra Morada Drive, which sits above a densely wooded arroyo. While lightning is the most common source of fires in the U.S., according to the National Fire Protection Association, investigators were able to rule that out quickly.