Here are five interesting facts about April 15 in Colorado history:

1. On April 15, 1920, the Colorado Anti-Discrimination League was founded in Denver, Colorado. The organization aimed to combat discrimination and prejudice based on race, color, religion, and national origin. The league played a major role in lobbying for anti-discrimination laws and supporting civil rights movements in Colorado.

2. In 1943, the Colorado Supreme Court ruled that cities and their police officers did not have the right to detain military personnel on leave or furlough for violating local laws, unless their offense was directly related to military discipline or security. The ruling came after a lawsuit filed by a Marine who was arrested in Denver for overstaying his parking meter.

3. On April 15, 1981, the Denver Nuggets defeated the Houston Rockets in a thrilling 163-155 NBA game, which still ranks as the highest-scoring game in NBA history. Nuggets’ guard Michael Adams recorded 45 points and 10 assists, while Rockets’ guard Calvin Murphy scored 57 points.

4. On this day in 1995, the Denver Broncos traded their star running back Bobby Humphrey to the Miami Dolphins for a sixth-round pick in the next year's draft. Humphrey had rushed for more than 3,000 yards in his first two seasons with the Broncos, but was sidelined by injuries and conflicts with the coaching staff.

5. The federal income tax deadline in the United States is typically on April 15, but due to the COVID-19 pandemic, the deadline for filing 2020 tax returns was extended to May 17, 2021. However, Colorado state income tax returns are still due on April 15.