1. In 1889, the first section of the Denver and Rio Grande Railroad was completed, stretching from Pueblo to Alamosa. This railroad played a significant role in the economic development of Colorado, connecting the state's interior to the rest of the country and facilitating the transport of goods and resources.

2. On October 20, 1942, the Rocky Mountain Arsenal was established in Denver. Built as part of the United States' efforts to expand its chemical weapons program during World War II, the arsenal later transitioned to producing other products, including pesticides, before being decommissioned in the 1990s.

3. October 20, 1978 saw the completion of the Eisenhower Tunnel, which runs beneath the Continental Divide on I-70. This tunnel, which is over 1.7 miles long, is the highest vehicular tunnel in the world, at an elevation of over 11,000 feet.

4. One of Colorado's most infamous criminal cases began on October 20, 1994, when John Albert Gardner III abducted and murdered Colorado girl Jessica Ridgeway. Gardner was eventually convicted and sentenced to life in prison without parole.

5. On October 20, 2011, the Colorado Avalanche retired the jersey of former player Peter Forsberg, who played for the team during two separate stints in the 1990s and 2000s. Forsberg was known for his skill as a playmaker and helped the Avalanche win two Stanley Cup championships.