1. Arizona became a state on February 14, 1912. However, December 31 holds significance as it was the last day of Arizona's territorial period. On this day in 1911, Arizona's territorial governor, Richard Sloan, officially resigned from his position, bringing an end to Arizona's territorial era.

2. On December 31, 1937, the greatest snowstorm in Arizona's history began. Over the next few days, Arizona experienced an unprecedented snowfall, with Flagstaff receiving over two feet of snow. The storm caused widespread damage and disrupted transportation across the state.

3. In December 1966, the University of Arizona defeated the University of Florida in the Gator Bowl, 27-7. This was Arizona's first major bowl victory and helped to establish the University of Arizona as a significant player in collegiate football.

4. On December 31, 1964, the Central Arizona Project was authorized by the federal government. Construction on this massive project began in 1973 and was completed in 1993. The project is responsible for collecting water from the Colorado River and delivering it to central and southern Arizona.

5. On New Year's Eve in 1986, a comet named Comet Halley passed by Earth, providing a spectacular sight in the Arizona night sky. At its closest point, the comet was visible to the naked eye and was a popular sight for many Arizonans who ventured outside to witness the event.