1. In 1870, the University of Colorado was founded in Boulder. Today, it is a well-respected institution with over 35,000 students.

2. On September 20, 1937, the first state park in Colorado was established. Eldorado Canyon State Park, located in Boulder County, offers visitors stunning outdoor recreation opportunities.

3. In 2004, the Democratic National Convention was held in Denver from August 25 to August 28, with September 20 being the final day of the event. Over the course of the convention, John Kerry was officially nominated as the Democratic candidate for president.

4. On September 20, 1859, gold was discovered at Gregory Gulch near Black Hawk, Colorado, which sparked the Colorado Gold Rush. The event led to an influx of miners and prospectors into the area, and Colorado's mining industry grew rapidly over the following decades.

5. In 2013, unprecedented flooding hit parts of Colorado, including Boulder County. September 20 was a particularly devastating day, with the town of Lyons being completely cut off by floodwaters. The floods caused billions of dollars in damage and resulted in numerous fatalities.