1. On September 21, 1904, the first automobile tunnel in the United States was completed in Colorado. The tunnel, located in Mount Carmel, allowed for easier travel through the mountains and paved the way for future infrastructure development in the state.

2. In 1937, the Colorado State Fair was held in Pueblo, Colorado, and featured a daring airplane stunt show. The pilots performed loops and dives in their planes, thrilling audiences with their aerial acrobatics.

3. On September 21, 1940, the famous author Jack Kerouac visited Denver, Colorado, and began writing his novel "On the Road" while staying in a hotel on Larimer Street. The novel would go on to become a classic of the Beat Generation, and Denver would be forever associated with its creation.

4. In 1999, a deadly tornado swept through the town of Holly, Colorado, killing 11 people and causing extensive damage to the area. The tornado was one of the most destructive in Colorado's history.

5. On September 21, 2014, the first-ever AIDS Walk Colorado was held in Denver. The event brought together thousands of people to raise awareness and funds for HIV/AIDS research and support services in the state.