Building the canyon's layers
When the layers at the bottom of the Grand Canyon formed 1.7 billion years ago, Arizona was at the western edge of North America. Collision with another landmass created a mountain range, remnants of which make up the Vishnu Schist. The mountains were eroded and covered by an ocean, which deposited more sediments. These too were uplifted, tilted, and eroded, creating the Great Unconformity. The third time the region was inundated by the sea, the 8-kilometer-thick sequence of Paleozoic sediments was laid down.