1. Cinco de Mayo: While it's not a specific event in Colorado history, Cinco de Mayo is celebrated each year on May 5th and has a special significance in Colorado. The state is home to a large Mexican-American population, and cities like Denver host parades and festivals to commemorate the holiday.

2. The Pueblo Revolt: On May 5, 1680, Native American tribes in New Mexico, led by the Pueblo people, launched a successful revolt against Spanish colonial rule. Although Colorado was not directly involved in this rebellion, it had significant repercussions for the region and helped shift the balance of power in the American Southwest.

3. The Silver Boom: May 5, 1878, marked the discovery of major silver deposits near Leadville, Colorado. This led to a spike in silver mining and a rush of settlers who hoped to strike it rich. The resulting boom and bust had a profound impact on the economy and culture of the region.

4. The Ludlow Massacre: On May 5, 1914, tensions between striking coal miners and the Colorado National Guard erupted into violence at the Ludlow mining camp near Trinidad. The resulting massacre claimed the lives of approximately two dozen people, including women and children, and became a defining moment in the history of the American labor movement.

5. The Colorado Rockies: On May 5, 1993, the Colorado Rockies played their first home game at Coors Field in Denver. The team, which had been founded two years earlier, quickly became a beloved fixture of the state's sports scene and helped put Colorado on the baseball map.