1. In 1859, the Colorado Gold Rush began when a group of prospectors discovered gold near present-day Denver. This event led to a population boom and the eventual statehood of Colorado.

2. On May 31, 1921, the first airplane to fly over the Rocky Mountains landed at Lowry Field in Denver. The flight was made by Lt. John Macready, who was later awarded the Distinguished Flying Cross for his accomplishment.

3. The deadliest avalanche in Colorado history occurred on May 31, 1979, in the San Juan Mountains. The disaster claimed the lives of eight people and highlighted the dangers of backcountry skiing.

4. On May 31, 2013, severe flooding struck the front range of Colorado, resulting in 10 fatalities and $2 billion in damage. The flooding was caused by heavy rain over several days and overwhelmed the state's infrastructure.

5. Colorado astronaut Steve Swanson launched on his second trip to space on May 31, 2014. Swanson, who was born in Syracuse, New York, attended the University of Colorado Boulder before embarking on a career at NASA.