1. California became a state: September 15, 1850 marks the day that California officially became the 31st state of the United States of America.

2. The San Francisco earthquake: In 1906, on September 15, a devastating earthquake struck San Francisco, leading to a massive fire that destroyed much of the city.

3. Mexican Independence Day: While not specific to California, September 15 is recognized as Mexican Independence Day, which celebrates the 1810 Cry of Dolores, a call to arms that initiated the Mexican War of Independence.

4. A famous comedian is born: September 15, 1903 is the birthday of legendary comedian Roy Acuff, who was one of the pioneers of country music.

5. The closing of the Golden Gate Bridge: On September 15, 1989, the Golden Gate Bridge was closed due to high winds, marking only the second time in its history that it had been closed for weather-related reasons.