1. In 1915, the smelter town of Hayden, Arizona experienced a devastating fire that destroyed many buildings and left thousands homeless.

2. On May 31, 1921, the historic Old Main building at the University of Arizona in Tucson was destroyed by a fire. The building was rebuilt and remains a prominent feature on the university's campus today.

3. In 1935, President Franklin D. Roosevelt dedicated the Hoover Dam, which sits on the border between Arizona and Nevada. The dam provides hydroelectric power, flood control, and irrigation for the surrounding areas.

4. On May 31, 1949, Arizona became the 48th state to ratify the 22nd Amendment to the United States Constitution, which limits the number of terms a president can serve.

5. The Phoenix Suns basketball team made their first NBA Finals appearance on May 31, 1976. They ultimately lost the championship to the Boston Celtics, but their success helped put Phoenix on the map as a major sports city.