Arizona - The Grand Canyon State

Map of North America during the mid-Cambrian
North America, 510 million years ago, click or tap to see a larger version


Geologically speaking, most of Arizona is composed of land that was accreted to the southwest edge of the Laurentia craton/North America plate in the Cretaceous Period of the Mesozoic Era (from about 146 million years ago to about 65 million years ago). Northeastern Arizona is mostly composed of the Colorado Plateau, a large chunk of ancient Rodinian desert pushed up about 65 million years ago. The edge of that uplift is known today as the Mogollon Rim. Arizona below the Rim is up to 3,000 feet lower in elevation and the drop-off from the Rim is pretty dramatic in many areas.

Prior to the Colorado Plateau uplift, northeastern Arizona was washed over many times by ocean and by rivers draining down from the Ancestral Rocky Mountains to the northeast. Most of the petrified logs exposed at Petrified Forest National Park were washed down up to 200 million years ago during the time of raging rivers: flooding waters washed whole logs downstream to where they finally rested in the river delta. There they were quickly sealed in by surrounding gravel and sands. Then the mineralization of the logs proceeded at a slow pace until today, what we see is mineralized wood.

North America 60 million years ago
North America during the Cenozoic Era, click or tap to see a larger version

90 million years ago the North American continent was bisected by the Western Interior Seaway, a shallow sea running east of the Cordilleran region to the western edge of the Laurentia craton. The Cordillera was pushed up during the collision of the Farallon plate with the North America plate.

The Colorado River breached the edge of the Colorado Plateau and began cutting down into the Grand Canyon about 5 million years ago. What really pushed the flow of the river in the direction it is in today was the rifting that created the Gulf of Baja California. That rifting spread cracks up along what is now the boundary of California and Arizona into the Virgin River area in northwestern Arizona.