Chinle Formation

The Chinle Formation is a Late Triassic continental rock unit made up of fluvial, lacustrine and palustrine to eolian deposits, mainly mudstone, siltstone and sandstone with paleosols throughout, dating to the Norian and Rhaetian stages. It extends across the Colorado Plateau region of Nevada, Utah, northern Arizona, western New Mexico and western Colorado, reaching a maximum thickness of a little over 520 meters in its southern portion; geologist Herbert E. Gregory formally named it in 1917 after Chinle Valley in Apache County, Arizona. The formation is particularly significant for its exceptional fossil record, containing a diverse array of extinct reptile, fish and plant fossils, including early dinosaurs and the famous petrified wood of Petrified Forest National Park in Arizona, and it has been crucial for understanding Late Triassic ecosystems and the earliest evolution of dinosaurs; the Ghost Ranch quarry in New Mexico is among its most scientifically valuable sites. This entity documents the Chinle Formation specifically as a geological formation, a Late Triassic continental sedimentary sequence.