El Centro is a city in and county seat of Imperial County, the largest city in the Imperial Valley, east anchor of the Southern California Border Region, and the core urban area and principal city of the El Centro metropolitan area which encompasses all of Imperial County. El Centro is also the largest American city to lie entirely below sea level (-39 feet). The city, located in the far southeastern corner of California, is near the major Southern California city of San Diego and the Mexican city of Mexicali.