1. The 1906 San Francisco Earthquake: On April 18, 1906, San Francisco was rocked by a massive earthquake that remains one of the deadliest and most destructive natural disasters in U.S. history. The quake, which had a magnitude of 7.9, destroyed much of the city and sparked a massive fire that raged for three days.

2. The First California Earth Day: In 1970, April 18 was celebrated as the first California Earth Day. This event was part of a larger, nationwide celebration of environmental awareness and conservation efforts, which ultimately led to the founding of the Environmental Protection Agency and other government initiatives to protect the environment.

3. The Golden Gate Bridge: On April 18, 1937, the Golden Gate Bridge officially opened to the public. This iconic landmark remains one of the most recognizable images of California and draws millions of visitors each year.

4. The Los Angeles Riots: In 1992, April 18 was the first day of riots that shook Los Angeles following the acquittal of police officers who had been accused of beating Rodney King. The riots lasted for six days and resulted in hundreds of injuries and several dozen deaths.

5. The Loma Prieta Earthquake: In 1989, a magnitude 6.9 earthquake struck the Bay Area, including the city of San Francisco. The quake, which was named after the nearby Loma Prieta Peak, caused widespread damage and resulted in over 60 deaths.