Final answer:
The Colorado River crosses northern Arizona, forming the Grand Canyon. Debate surrounds the canyon's formation, with theories ranging from 5 to 70 million years ago, based on rock layers and fault lines.
Step-by-step explanation:
The river that crosses the northern portion of Arizona and forms the Grand Canyon is the Colorado River. This remarkable river has carved the Grand Canyon over millions of years, and the processes involved have intrigued scientists and researchers alike.
The formation of the Grand Canyon is a topic of debate, with some suggesting it began only 5 million years ago as the Colorado River cut through the rock layers, while others believe it started forming up to 70 million years ago during the Laramide orogeny, based on the stratigraphy and fault lines that the river intersects.
Artwork like 'The Grand Canyon of the Colorado River' by Moran and detailed geological maps, such as the one by Billingsley, provide us with insights into the awe-inspiring landscape and its complex geology.
In addition, the Hoover Dam is a significant landmark on the Colorado River, demonstrating the river's importance beyond its natural beauty, offering essential water resources to millions of people and vast agricultural areas in the southwestern United States.