1. In 1894, May 1st marked the first officially recognized Labor Day celebration in Colorado. The holiday was originally created to honor the contributions and sacrifices of the working class and promote fair labor conditions.

2. May 1, 1915, marked the opening of Colorado's Red Rocks Amphitheatre. The iconic venue, known for its natural acoustics and stunning red rock formations, has since become a beloved destination for music lovers and outdoor enthusiasts alike.

3. May 1, 1936, marked the completion of the Hoover Dam, which was built on the Colorado River at the Nevada-Arizona border. The dam was a massive engineering feat that created a major source of hydroelectric power and helped protect the region from devastating floods.

4. On May 1, 1971, Colorado became the first state in the country to decriminalize marijuana. While possession of small amounts of cannabis was still subject to a fine, the move marked a significant shift in public attitudes towards the drug and helped pave the way for further legalization efforts.

5. In more recent years, May 1st has become a significant date for immigration rights activists in Colorado and around the country. In 2006, a massive nationwide protest movement known as the "Great American Boycott" took place on May 1st, with millions of people staging walkouts and rallies to demand immigration reform and more humane treatment of undocumented immigrants.