1. On September 12, 1855, William Walker declared himself the President of Baja California. Walker was an American adventurer who attempted to create a republic in Baja California with himself as the leader. His attempt ultimately failed, and he was forced to flee to the United States.

2. The famous Hollywood Bowl opened on September 12, 1922. The Hollywood Bowl is an outdoor amphitheater located in the Hollywood Hills of Los Angeles. It is a popular venue for concerts and other cultural events and has hosted many famous musicians and performers over the years.

3. On September 12, 1940, construction began on the San Francisco Bay Bridge. The Bay Bridge spans the San Francisco Bay and connects San Francisco with Oakland and other East Bay cities. It was completed in 1936 and is now an iconic feature of the San Francisco skyline.

4. The California State Legislature passed a bill legalizing recreational marijuana on September 12, 2017. This made California the largest state in the US to legalize the use of cannabis for recreational purposes.

5. September 12, 2018, marked the 130th anniversary of the Great 1888 Temescal Shootout. The shootout was a violent confrontation between the American settlers and Native American tribes in Temescal Valley in Riverside County. It lasted for several days and resulted in the deaths of many people, including women and children. The incident is considered one of the bloodiest events in California's history.