1. On December 18, 1915, the historic hotel-del-coronado in San Diego hosted the first transcontinental telephone call in the United States.

2. In 1932, the Diablo Dam on the Skagit River in Washington state was dedicated, providing cheap hydroelectricity to the Skagit Valley and power to the growing city of Seattle, some 80 miles to the south. California's Pacific Gas and Electric Company provided important financial backing for the project.

3. December 18, 1944, saw the historic formation of the United Nations Monetary and Financial Conference in Bretton Woods, New Hampshire. Seventy-fve countries, including the United States, attended the three-week conference held at the Mount Washington Hotel. Prominent delegates from California included Harry Dexter White, Assistant Secretary of the Treasury, and John Maynard Keynes, British economist.

4. On December 18, 1961, the San Francisco Giants added another future Hall of Famer to their roster, acquiring outfielder Willie Mays from the New York Mets in exchange for pitcher Ray Daviault and outfielder/outfielder Jay Daviault. Mays went on to play in five World Series with the Giants and became one of the greatest players in baseball history.

5. December 18, 2017 was a significant day in California history as the state officially began the legal sale of recreational cannabis. The industry has since grown significantly, with over $3 billion in sales in 2020, generating an estimated $1 billion in tax revenue for the state.