1. The United States officially acquired California on December 12, 1850. California was ceded to the United States by Mexico as a result of the Mexican-American War.

2. On December 12, 2017, the Thomas Fire broke out in Ventura County. It became the largest wildfire in California's modern history, burning over 280,000 acres and destroying over 1,000 structures.

3. The first baseball game played under electric lights in California was on December 12, 1889, at Recreation Park in San Francisco. Teams from San Francisco and Oakland played under newly installed electric lights, which allowed the game to continue beyond sunset.

4. On December 12, 1968, the Zodiac Killer struck again in San Francisco. He attacked Bryan Hartnell and Cecelia Shepard at Lake Berryessa, leaving Shepard dead and Hartnell seriously injured.

5. December 12, 1992, marked the grand opening of the Anaheim Transportation Center in Orange County. The center serves as an Amtrak, Metrolink, and bus station, connecting commuters and travelers to various parts of Southern California.