1. On April 21, 1871, Bisbee, Arizona was founded after prospector George Warren discovered copper deposits in the nearby Mule Mountains. The town quickly grew and became a major mining center in the early 20th century.

2. In 1930, on April 21, the Hoover Dam, located on the border between Arizona and Nevada, began construction. The dam was completed in 1936 and provides electrical power, flood control, and water storage for the region.

3. On April 21, 1941, Luke Air Force Base was established near Phoenix, Arizona. The base played a key role in training pilots during World War II and continues to be an important training center for the U.S. Air Force today.

4. In 1997, on April 21, the Phoenix Suns basketball team played their final game at the historic Veterans Memorial Coliseum before moving to a new arena. The Coliseum had been their home for over 25 years and was the site of many memorable games and events.

5. On April 21, 2010, the Deepwater Horizon oil rig exploded in the Gulf of Mexico, causing the largest oil spill in U.S. history. While the disaster did not occur in Arizona, it had a significant impact on the state's economy, particularly in the tourism and fishing industries.