Backing up to around the start of the 1700's, Spanish people arrived in California and settled there, this was when California wasn't a state of America. It became a state in 1847, which was a treaty to end the American-Mexican war, making California the 31st state.
The next year in 1848, California became much more popular when gold was discovered there, which attracted large amounts of people to settle there to seek wealth, fortune and opportunity.
In the early 1900's the state became even more popular as it had a large role in the film industry, creating Hollywood and movies for the public to enjoy. It soon became the most populous state with the largest economy.
Before the outbreak, California seemed to be going along normally with the rest of the world. However, there were reports of a recent "flu" which meant hospitals coped with more patients and citizens getting flu shots in order to prevent getting sick from this flu. Videos and information emerged on certain websites showing people with a strange virus attacking people, however, only very few people saw this media, one of which was Tobias.
Soon, an unknown Los Angeles radio station was informing people to get their flu shots if they haven't yet. People began to disappear and hospitals were very slowly becoming more overcrowded with sick patients. During a ride home from Paul R. Williams High School, Madison noticed a fence with half a dozen "Missing" papers and a park devoid of activity, with the exception of a mysterious human like figure shambling towards the main road as if drunk (the implication is that it was Zombie).
That night, a shootout happened on a highway, involving members of the California Highway Patrol and a man who came back to life after an automobile accident and attacked several emergency service workers. The footage (which was captured by several bystanders and news media outlets) was leaked online to more popular websites, meaning many members of the public saw it and began to panic, especially citizens in Los Angeles, meaning many people decided not to go to school/work that day.
Later that morning, Art Costa, the Principal, saw staff members watching the leaked video and told them he'd talk to the other schools about it. Soon enough, Paul R. Williams High School decided to have a half-day along with other schools in the Los Angeles area and confused students began to pile onto the bus, going home.
When Madison and Travis decide to go east as they're worried about the illness, Travis had to go get his ex-wife Liza and his son, Chris. Meanwhile, Chris was on a public bus in a neighborhood close to Downtown LA when a pedestrian jumped onto the bus and claimed the Police just shot a homeless man for no reason. Police radio chatter indicate that there has been a spike in police shooting.
The more suburban parts of LA, and possibly all of California, begin getting more congestion on roads as more people become aware of the illness and try to flee the city. Police were instructed to store up on supplies such as food, gas and water and were told not to tell anyone the real situation. There were more broadcasts on media such as radio, which could have been ordered by the Californian government. The broadcasts told people if they don't need to travel then don't but if they did, then proceed with caution, which made even more people worried.
Emergency services were keeping the area contained and secure but were failing due to the sheer amount of angry people outraged over the police shooting a homeless man, this soon triggered a protest, which was broadcast on the news. When Travis and Liza find their son, one LAPD member, Gonzales, shot an infected woman, causing protesters and witnesses to flee scene but also triggering a riot. Riot control was called in and people began to either continue causing violence or to flee the area.
The riots presumably lasted the majority of the night in Los Angeles, San Diego and possibly other cities such as San Francisco. Rioters ignored Police orders to clear the streets and to stop, making them easy targets to the infected. Flights were cancelled by the FAA to reduce the spreading of the illness (evidence for this was seen in promotional material released for Fear). Power stations began to fail, causing mass blackouts in LA and other settlements in California. Mid-flight of Flight 462, Jake Powell, and perhaps other passengers witnessed lights going out in Phoinex, Arizona. According to Deirdre, an air attendant on TruWest Airlines Flight 462, the pilot was informed that lights were going out everywhere, including California, and the pilot hoped to use San Francisco as an alternate landing destination.
As people in the Los Angeles borough and other areas of the state panicked to take their loved ones to the hospital, it caused hospitals to be overrun and be abandoned. One final state radio message was played, stating that California has declared a state of emergency along with other states and that the National Guard will be deployed.
Morning rose on California, which remained in ruins. Cities such as LA had gridlocked highways and burning neighborhoods and smoke rising from high rises. The National Guard was called in by the Governor of California in order to set up safe zones in Los Angeles and possibly other cities. In Los Angeles, they set up twelve safe zones around the city, which went under the name Los Angeles Basin Safe Zones; one safe zone was in El Sereno. They also made a private facility from a college which was named The Compound. Its use was a base of operations for the Los Angeles District and to keep people who may have the virus locked up.The National Guard shared very little information about the outside world to the residents in the safe zones. It was rumored that most people decided to go east, to Bakersfield and Las Vegas.
The National Guard previously had a center for the sick and needy at the Los Angeles Memorial Sports Arena, which hosted 2,000 citizens but it was overrun and the National Guard decided to lock it up, leaving the uninfected to be trapped with the infected.
The National Guard originally planned for a "big push to take back the city" but it either never happened or it failed. This could have been the same for San Diego and other cities. A few days later, at night, Madison, Daniel Salazar and and the others managed to get The Compound overrun with infected, meaning military personnel had to evacuate elsewhere. They left behind a handful of doctors and researchers and even their own, showing how ruthless they are. They evacuated to Edwards Air Force Base, which was (and could still be) active and played a key role in Operation Colbalt; the bombings.
Eventually, when all hope was lost and Operation Cobalt was under way, the national guard fled the safe-zones and the military napalmed Los Angeles, San Diego, San Francisco and other cities and settlements in California. It could be possible San Diego got it worse during Operation Colbalt as they say it was "completely" burnt.