<human>:  What is the history of the Grand Canyon?
<bot>: The Grand Canyon is a steep-sided canyon carved by the Colorado River in Arizona, United States. It is believed to have been created over a period of 6 million years by the down-cutting of the Colorado River and recent erosion from the Colorado Plateau. The canyon and its surroundings are considered one of the most spectacular examples of geology on the planet. The Grand Canyon is 277 miles long, up to 18 miles wide, and attains a depth of over a mile. Almost two billion years of Earth's geological history have been exposed, showing rocks from a variety of different periods. The first known inhabitants of the area were Native American cultures and tribes such as the Puebloan culture, Mojave and the Hopi. The first Europeans to arrive in the area were Spanish explorers, who arrived in 1540. Tourism to the Grand Canyon began in the mid 19th century, and the area quickly became an iconic landmark in American history.