There is a potentially active rupture zone (defined as a fault that has been active during quaternary time – the last 2,000,000 years) existing immediately east of the City limits running parallel and adjacent to the shoreline of Clear Lake. Within the past 200 years, no major potentially damaging earthquakes have occurred along any faults within Lake County, including the Big Valley fault adjacent to the eastern City boundaries. Geologically, recent faulting is indicated, however, by the apparent displacement of quaternary earth materials along the Big Valley fault.