GAVIN NEWSOM. The mayor of San Francisco will soon be presented with a bill voted almost unanimously yesterday by the board of supervisors to ban petroleum-based plastic grocery bags from the city. SF generates 180 million of these bags which, hard to recycle, cover the earth. Sort of like a cross between kudzu and Christo. Biodegradable ones are more expensive but the city is betting the costs will decrease as they become more common. Good News Dept.