There’s a crack in California. It stretches for 800 miles, from the Salton Sea in the south, to Cape Mendocino in the north. It runs through vineyards and subway stations, power lines and water mains. Millions live and work alongside the crack, many passing over it (966 roads cross the line) every day. For most, it warrants hardly a thought. Yet in an instant, that crack, the San Andreas fault line, could ruin lives and cripple the national economy.