1. Cesar Chavez Day
March 31 is celebrated in California as Cesar Chavez Day, in honor of the civil rights activist who co-founded the United Farm Workers (UFW) and fought for the rights of agricultural workers. It was first observed as a state holiday in California in 2000.

2. California's First Elevator
On March 31, 1857, the first hydraulic elevator in California was installed in a building on Montgomery Street in San Francisco. The elevator was designed by Elisha Otis, who later became famous for inventing the safety brake that made modern elevators possible.

3. Golden Gate Bridge Construction Begins
Construction of the iconic Golden Gate Bridge in San Francisco began on March 31, 1933. The bridge, which spans the Golden Gate Strait between San Francisco and Marin County, took four years to complete and opened to the public in 1937.

4. Disneyland Groundbreaking Ceremony
On March 31, 1954, a groundbreaking ceremony was held for Disneyland, the famous theme park in Anaheim, California. Walt Disney had chosen the site for its proximity to Los Angeles and because he wanted a park that parents and children could enjoy together.

5. Earth Hour
March 31 is also known as Earth Hour, a global event where people turn off their lights for one hour to raise awareness of climate change and the need for environmental action. The first Earth Hour was held in Sydney, Australia in 2007 and has since spread to more than 180 countries around the world.