In the Ohlone Wilderness south of Pleasanton is a 220-foot-tall reminder that the past may catch up with California. Calaveras Dam – built by the City of San Francisco 92 years ago – sits next to an active earthquake fault. Downstream are Fremont and other communities along Alameda Creek where 300,000 people live who are considered at risk in a major quake. The dam’s base is comprised of loose earth from a previous dam that had failed earlier in the 20th century. It was back in the day when quake knowledge was just barely out of the Stone Age.