A wildfire in the ritzy Bel-Air neighborhood of Los Angeles that destroyed six homes and damaged a dozen more last week was sparked by “illegal cooking” in a homeless camp, authorities said Tuesday. The Skirball Fire, one of at least five to erupt in Southern California last week, was traced back to an encampment underneath an overpass in a brush area. “It does appear as if people were sleeping and cooking in that area. The fire department was not aware of this encampment prior to the fire,” Capt. Erik Scott of the Los Angeles Fire Department told reporters. The fire, which also prompted the evacuation of 700 homes in Bel-Air, was 85 percent contained as of Tuesday. A larger fire northwest of Los Angeles, the Thomas Fire, continued to rage Tuesday, with authorities extending a red-flag warning for the fourth time since the blaze erupted last Monday. The fire, which has scorched at least three counties, was 25 percent contained as of Tuesday, but wind gusts later this week are expected to stoke the flames again.