Uplift and erosion
About 70 million years ago, the region of what is now northern Arizona started to rise. This led to higher rates of erosion, as rivers cut through the rising land. Then, about five million years ago, the Gulf of California, more than 500 kilometers to the south, began to open. The large difference in elevation between the high plateau and this new arm of the ocean caused rivers to erode into one another, creating one large river. The new river rapidly eroded a channel from the Gulf of California to the Colorado Plateau. This was the birth of the Grand Canyon.