1. On May 4, 1927, the first-ever air mail flight between the United States and Mexico was made. The flight took off from San Diego, California, and flew to Tijuana, Mexico, carrying over 50 pounds of mail.

2. In 1970, on May 4, four students were shot and killed by National Guardsmen at Kent State University in Ohio. The tragic incident sparked protests and demonstrations across the nation, including in California.

3. On May 4, 1981, Ronald Reagan was shot and wounded by John Hinckley Jr. outside a hotel in Washington, D.C. at the time, Reagan was the 40th President of the United States, having previously been governor of California.

4. May 4, 1932 marked the opening day of the Pacific Coast League baseball season. The league, which consisted of several teams from California, Oregon, and Washington, was one of the most popular minor league baseball organizations in the country.

5. On May 4, 1904, the Southern Pacific Railroad completed construction of the Cascade Tunnel, a nearly 8-mile-long tunnel through the Cascade Mountains in Washington state. The tunnel allowed for improved transportation links between California and the Pacific Northwest.