1. On September 5, 1913, the Denver and Salt Lake Railway was completed, opening access to the state's Western Slope for trade and tourism. The railway ran from Denver to Salt Lake City, passing through scenic areas such as Glenwood Canyon and the Moffat Tunnel.

2. In 1960, on September 5th, the United States Senate gave its final approval for the construction of the Fryingpan-Arkansas Project, a major water diversion project in eastern Colorado. The project allowed for the development of new agricultural and urban areas in the Arkansas River basin, but also caused environmental damage to the state's rivers and wetlands.

3. September 5, 1870, marked the opening of the University of Denver, Colorado's oldest private university. Founded by Methodists, the university initially focused on theological education but has since expanded to offer a broad range of undergraduate and graduate degree programs.

4. On September 5, 2013, Colorado experienced massive flooding caused by heavy rains that began on September 9th. The flooding caused widespread damage to homes, businesses, and infrastructure, and resulted in the deaths of ten people. The disaster prompted large-scale rescue and relief efforts from the state and federal governments.

5. September 5, 1970, saw the opening of the Pike National Forest Scenic Byway, a 51-mile route through the Pike National Forest southwest of Denver. The byway offers stunning views of the Rocky Mountains as well as access to hiking trails, camping areas, and other outdoor recreational opportunities.