In a sprawling shantytown between the Salton Sea and a toxic dump site, children play barefoot on dirt roads, running beside leaking sewer lines and piles of rotting garbage thick with flies. Beneath their feet is broken glass; nearby, rusting machinery and wire. When the wind kicks up, they breathe dust and ash from an adjacent dump that contains elevated levels of cancer-causing dioxins. Their families are mostly farm workers who live in hundreds of hot and dilapidated trailers, many of them missing windows and siding. When the water pressure dropped a week ago, some residents collected the few drips...