1. On October 15, 1987, a major earthquake measuring 5.9 on the Richter scale struck the Los Angeles area. The earthquake caused significant damage to buildings and infrastructure in the area, and resulted in several deaths and injuries.

2. On October 15, 1915, the Panama-Pacific International Exposition opened in San Francisco. The Exposition was held to celebrate the completion of the Panama Canal and to spotlight the achievements of the city of San Francisco. The Exposition featured exhibits from around the world, including several large-scale buildings and monuments.

3. On October 15, 1964, civil rights activist Mario Savio delivered a passionate speech at the University of California, Berkeley, sparking the Free Speech Movement. The movement would go on to become a major force for change in American politics, and the speech remains an important moment in the history of protest and civil rights.

4. On October 15, 1956, the Mission San Juan Capistrano was designated a National Historic Landmark by the United States government. The mission, founded in 1776, is one of the most important historic sites in California and played a significant role in the state's early history.

5. On October 15, 1752, Spanish explorer Juan Bautista de Anza was born in Sonora, Mexico. Anza is best known for his exploration of California and the American Southwest, which helped to open up the region to settlement and development. He is considered one of the most important figures in the early history of California.