1. Pioneers Settled in Mesa: On July 15, 1878, a group of pioneers led by Daniel Webster Jones settled in Mesa, Arizona, and established the Mesa City Colony. The colony's main objective was to build a viable agricultural community in the area.

2. Arizona Statehood Day: July 15 is celebrated as Arizona Statehood Day because on this day in 1911, President William Howard Taft signed a proclamation declaring Arizona the 48th state of the United States.

3. The Tonto National Forest was Established: On July 15, 1902, President Theodore Roosevelt established the Tonto National Forest in Arizona. It is the fifth-largest forest in the United States and covers about three million acres.

4. Arizona's First Spanish-Language Newspaper: Arizona's first Spanish-language newspaper, El Mexicano, was published on July 15, 1921, in Tucson. It was established by Ramón Gutiérrez, a Mexican immigrant who wanted to provide news to the Spanish-speaking community in Arizona.

5. Grand Canyon National Monument: On July 15, 1908, President Theodore Roosevelt declared the Grand Canyon a National Monument. It was later designated as a National Park in 1919, making it one of the most visited parks in the United States.