California was a U.S. State located in the western United States on the coastline. It was the most populous state as well as the 3rd largest in area. It's bordered by Oregon to the North, Nevada and Arizona to the East, as well as the international border with Mexico to the South. Its capital was Sacramento.
Los Angeles was mostly shown, being the home of Jackson Curtis and his separated family. The ship that Harry Helmsley and Tony Delgatto leave on is presumably on the California coastline as it takes place in the San Francisco Bay and the governor's office in Sacramento is shown on TV as the governor speaks.
When the 2012 apocalypse occurred, the San Andreas Fault entirely cracked, triggering a 10.9 magnitude earthquake which caused most of the state to separate from the continental United States and sink into the Pacific Ocean.