1. On December 20, 1871, the Colorado Women's Suffrage Association was founded in Denver. This association played a pivotal role in securing the right to vote for women in Colorado in 1893, 27 years before the passage of the 19th Amendment to the U.S. Constitution.

2. In 1894, the Denver and Rio Grande Railroad completed construction of the Royal Gorge Bridge, the highest suspension bridge in the world at the time. The bridge spans the Royal Gorge, a narrow canyon on the Arkansas River, and stands 956 feet above the river below.

3. On December 20, 1910, the first flight of an airplane in Colorado was made by John Carey at Overland Park in Denver. Carey flew a Wright Brothers Model B biplane, which had been shipped to Denver by train.

4. The deadliest avalanche in Colorado history occurred on December 20, 1964, on the slopes of Mount Sniktau near Loveland Pass. The slide killed nine skiers and snowboarders who were participating in a backcountry competition. The tragedy led to increased awareness of avalanche safety and the development of better forecasting techniques.

5. On December 20, 2008, the Colorado Rockies signed pitcher Huston Street to a three-year contract. Street went on to have a successful tenure with the Rockies, earning an All-Star selection in 2010 and helping the team reach the postseason in 2009 and 2017.