1. On April 4, 1949, the University of Arizona inaugurated its new president, Richard A. Harvill, who served as president for 23 years until his retirement in 1971. During his tenure, Harvill oversaw significant expansions in facilities, research, and academic programs at the university, and he played a key role in establishing the University Medical Center in Tucson.

2. April 4, 1968 was a tragic day in Arizona history, as it was the day that civil rights leader Martin Luther King Jr. was assassinated in Memphis, Tennessee. King's death sparked protests and riots across the country, including in Arizona, where demonstrators gathered in Phoenix to mourn and call for an end to racial injustice.

3. Arizona's first major earthquake of the 20th century occurred on April 4, 1910, with a magnitude estimated at 6.5. The quake was centered along the Arizona-New Mexico border and caused significant damage and several injuries in the nearby town of Douglas.

4. On April 4, 1945, the U.S. Army's 10th Mountain Division, based in Colorado, began a three-day training exercise in the rugged terrain of the Superstition Mountains east of Phoenix. The exercise was part of the division's preparations for combat in the Italian Alps during World War II, where they fought against German troops in some of the most challenging mountain terrain in the world.

5. On April 4, 1974, Arizona State University's iconic Sun Devil Stadium hosted its first concert, headlined by legendary rock group The Rolling Stones. The stadium has since become one of the premier concert venues in the Southwest, hosting countless famous bands and musicians over the years.