GRAND STAIRCASE, SOUTHERN UTAH
Age of the Dinosaurs
Mesozoic Era — 252 to 66 million years ago
Stand on the rim of the Grand Canyon. All of the rock units exposed as horizontal layers are of the Paleozoic Era, that is, older than 251 million years. Beneath them are rocks that form the steep walls of the inner canyon, which are even older. There are no remnants of dinosaurs in any of those rocks. Dinosaurs are of a more recent era, the Mesozoic. Rocks of that era are found across much of the western United States. In particular, one can gaze on the entire Mesozoic Era by standing at a viewpoint known as the Le Fevre Overlook and Rest Area along the side of State Highway 89A just south of Fredonia, Arizona. From there, one sees one of the most impressive geologic sequences in the world: The Grand Staircase.
Steps of the Grand Staircase as seen from the Le Fevre Overlook and Rest Area.
Clarence Dutton, in his 1882 publication The Physical Geology of the Grand Canon District, first called attention to this remarkable arrangement of five cliffs, calling it "the great stairway." (It was Charles Keyes who in 1924 first referred to the arrangement as "The Grand Staircase."). Closest to the Le Fevre Overlook are the Chocolate Cliffs (Moenkopi Formation). Then, in sequence as one climbs higher on the staircase, are the Vermilion Cliffs (Windgate Sandstone and Moenave and Kayenta formations), the White Cliffs (Navajo Sandstone), the Gray Cliffs (Dakota Sandstone) and the Pink Cliffs (Claron Formation).
The rocks of the Chocolate Cliffs formed before there were any dinosaurs on the planet. By time of the Vermilion Cliffs, there was the beginning of dinosaurs roaming the landscape. More occupied the planet during the deposition of the White Cliffs. Dinosaurs dominate the world during the deposition of the Gray Cliffs. The Pink Cliffs represent a step into the next geologic era, the Cenozoic. By then, the dinosaurs (at least, the non-avian dinosaurs) have become extinction.
Vermilion Cliffs in Vermilion Cliffs National Monument in southern Utah.