Southern California is the primary locus in the core manual. The introductory campaign takes place within and around Los Angeles in particular. These stories were written primarily by Andrew and Jack Gross. While these were written for a broad audience and it's hopefully not necessary for players to be acquainted with Los Angeles to appreciate these, they are also intended to capture fond attachments to (and sometimes loving mockery of) the city of Angels that the writers hope feel familiar to anyone who calls the area around the Santa Monica Bay home.
Resources include the core manual and the adventures in Campaign 1: Regulation.