1. On April 20, 1999, the Columbine High School shooting occurred in Littleton, Colorado, which resulted in the deaths of 13 people, including 12 students and one teacher.

2. April 20 marks the anniversary of the legalization of recreational marijuana in Colorado, which occurred on April 20, 2014. It was the first state in the US to legalize marijuana for recreational use.

3. In 2009, April 20 was declared "Rocky Mountain Oyster Day" in Colorado. Rocky Mountain oysters are a delicacy made from bull or sheep testicles, often served at local festivals and restaurants.

4. On April 20, 1889, the Colorado Fuel and Iron Company was founded by John Cleveland Osgood in Pueblo, Colorado. The company played a significant role in the state's mining and steel industries.

5. April 20 is also known as "420 Day," a popular celebration of cannabis culture. The origins of the term are debated, but it is widely believed to have originated from a group of high school students in California in the 1970s. In recent years, 420 Day celebrations have become more mainstream and often include public rallies, concerts, and festivals.