1. In 1863, the New Mexico Territory was split, and the eastern portion became the Arizona Territory. This historic event happened on September 18, making it a significant date in the state's history.

2. The infamous gunfight at the OK Corral in Tombstone occurred on October 26, 1881. However, the events leading up to the gunfight began on September 18 when a group of cowboys, including Tom and Frank McLaury and Billy Clanton, rode into Tombstone with a cache of stolen horses.

3. In 1903, President Theodore Roosevelt issued an executive order to establish the Tonto National Forest in Arizona. The forest covers over 2.8 million acres and is the fifth-largest national forest in the United States. The order was signed on September 18, making it an essential date in Arizona's environmental history.

4. The University of Arizona, commonly referred to as U of A, was founded on September 18, 1891. It was the first university in the Arizona Territory and is now a public research university located in Tucson.

5. In 1999, an earthquake measuring 5.2 on the Richter scale struck the Phoenix metropolitan area. The earthquake was centered near the city of Tempe and caused minor damage. The event serves as a reminder that earthquakes can happen anywhere, including in the middle of the desert.