Thousands of people opposed to the oil and gas drilling process known as “fracking” marched in Oakland, California, Saturday in what organizers called the largest anti-fracking protest in the United States. Demonstrators called on California Gov. Jerry Brown to ban fracking, citing concerns over pollution, poisoning of water supplies and climate change. A day earlier, 12 people were arrested as protesters blocked the entrance to Brown’s San Francisco office and erected a 16-foot fracking rig in the middle of an intersection. Brown was sworn in for a fourth term last month with a promise to address climate change.