# Chinle Formation Canonical page: https://lithomap.app/resources/geologic-formations/united-states/chinle-formation Last reviewed: September 17, 2026 Page purpose: Comprehensive United States geologic formation reference for human readers, search systems, and language models. Major region: Colorado Plateau / Rockies Regional setting: Colorado Plateau and adjoining Southwest Age: Late Triassic Age detail: Broadly about 230–201 million years ago; exact ranges vary by member and region Depositional setting: River systems, floodplains, lakes, and wetlands Rock types: Mudstone, Siltstone, Sandstone, Conglomerate, Limestone States in recognized usage: Arizona, Colorado, Nevada, New Mexico, Texas, Utah ## Summary The Chinle is a colorful Late Triassic river-and-floodplain record of the American Southwest, celebrated for petrified wood and for fossils that document ecosystems long before the rise of familiar Jurassic dinosaurs. ## Distribution Chinle rocks crop out widely across the Colorado Plateau and neighboring regions. The name is used at formation rank in many areas and at group rank in others, particularly where geologists divide the succession into several formations. Its cliffs, slopes, and painted badlands vary by member. Resistant sandstone and conglomerate commonly trace former channels, while red, purple, gray, and green mudstones form softer slopes. The Petrified Forest Member is only one part of this complex succession. ## Geological history Large river systems carried sediment across a broad continental basin. Channels shifted across floodplains dotted with ponds, lakes, and wetlands. Volcanic ash mixed with floodplain mud and later altered to clay, contributing to both the unit’s colors and its unstable, swelling slopes. Regional differences in source area, river style, and basin position produced many named members. Contacts and terminology have also changed through scientific study, so current state and federal maps should guide local usage. ## Fossil record Petrified conifer wood is the signature fossil, locally preserving growth rings and cellular structure. The formation also contains other plant remains, pollen, fish, amphibians, reptiles, early dinosaurs, and crocodile-line archosaurs such as phytosaurs and aetosaurs. Fossil abundance is member- and locality-specific. Mineral replacement turned some buried logs to stone, but most wood decayed. Even inside a famous fossil-bearing unit, a particular exposure may contain no visible fossils. ## Minerals and geological resources Quartz is abundant in sandstone and in much petrified wood; chalcedony is a common microcrystalline form of silica in silicified logs. Iron oxides and hydroxides contribute red, yellow, and brown colors, while manganese oxides can add darker tones. Clay minerals are abundant in mudstone and altered ash. Uranium and copper mineralization occurs locally in channel sandstones and has supported historic mining districts, but it is highly localized and can create radiation, contamination, and abandoned-mine hazards. ## Field context - Chinle mudstone can be impassable when wet and can fail as swelling clay beneath roads or trails. - Petrified wood is protected in national parks and may be restricted on other public lands; confirm the exact land manager’s rule. - Do not enter historic uranium workings or handle unknown mine waste. ## Connected field guides - Mudstone (rock; Named rock type and mineral context) — https://lithomap.app/resources/rock-identification/mudstone - Sandstone (rock; Named rock type and mineral context) — https://lithomap.app/resources/rock-identification/sandstone - Conglomerate (rock; Named rock type) — https://lithomap.app/resources/rock-identification/conglomerate - Limestone (rock; Named rock type) — https://lithomap.app/resources/rock-identification/limestone - Siltstone (rock; Named rock type) — https://lithomap.app/resources/rock-identification/siltstone - Copper (mineral; Mineral discussed in this formation) — https://lithomap.app/resources/mineral-identification/copper Mapped location and formation context support an identification but cannot establish one. Compare several physical properties and use laboratory analysis when the material remains ambiguous. ## Connected state geology guides - Utah geology — https://lithomap.app/resources/geology/united-states/utah - Colorado geology — https://lithomap.app/resources/geology/united-states/colorado - Arizona geology — https://lithomap.app/resources/geology/united-states/arizona ## Authoritative sources - Geolex Chinle unit record — U.S. Geological Survey: https://ngmdb.usgs.gov/Geolex/Units/Chinle_4997.html - Geolex Chinle references — U.S. Geological Survey: https://ngmdb.usgs.gov/Geolex/UnitRefs/ChinleRefs_4997.html - Secrets of the Chinle Formation — National Park Service: https://www.nps.gov/zion/learn/nature/secrets-of-the-chinle-formation.htm ## Formation photograph - Image: https://lithomap.app/_delivery/formations/chinle-formation.webp - Description: Multicolored badlands carved into the Chinle Formation - Creator: Creator not stated - License: Public domain — https://creativecommons.org/publicdomain/mark/1.0/ - Source record: https://commons.wikimedia.org/wiki/File:Chinle_Badlands.jpg Formation-level information does not prove that a fossil or mineral occurs at a specific coordinate. It also does not establish ownership, access, collecting permission, present conditions, or specimen identity.