1. In 1847, the Mexican-American war ended with the signing of the Treaty of Guadalupe Hidalgo. This treaty ceded California and other territories to the United States.

2. In 1932, the Winter Olympics were hosted in Lake Placid, New York. However, California-born athlete Eddie Eagan won the gold medal in the two-man bobsled event, becoming the only person to win gold medals in both the Summer and Winter Olympics in different sports.

3. In 1974, the groundbreaking ceremony for the BART (Bay Area Rapid Transit) subway system was held. This transportation system connects San Francisco with other Bay Area cities and is still in operation today.

4. In 1997, a powerful earthquake with a magnitude of 6.6 struck the San Francisco Bay Area, causing widespread damage and triggering fires in several areas. The quake caused over $1 billion in damages and resulted in 57 deaths.

5. In 2004, the social networking site Facebook was launched by Mark Zuckerberg and a group of fellow students at Harvard University. The site quickly grew in popularity and eventually became one of the most influential platforms in the world. Today, Facebook is used by over 2.8 billion people worldwide.