Chinle Formation

Chinle paleomap 220 Ma
Depiction of the Colorado Plateau region during the deposition of the Chinle Formation, ~220 million years ago. Location of Zion is starred.

Paleogeographic map courtesy of Ron Blakey, Colorado Plateau Geosystems, Inc.

 
Shinarump Member of Chinle Formation
Outcrop of the Shinarump Member, near the trailhead of the Chinle Trail.

NPS photo/Adrienne Fitzgerald

Late Triassic
~210-225 million years ago

The Chinle Formation consists of mudstone, siltstone, sandstone, and conglomerate that were deposited in the channels and floodplains of a large river system.

The bottom portion of the Chinle Formation is called the Shinarump Conglomerate Member, consisting of gravel and cobble-filled conglomerates deposited by high-energy braided rivers.

 
colorful bentonite of the Chinle Formation
Petrified Forest Member of the Chinle Formation

NPS photo

The upper portion of the Chinle in Zion is the Petrified Forest Member, composed largely of mudstones deposited by much lower-energy meandering rivers. The layers of brightly-colored mudstone are composed largely of bentonite clay, the result of weathering of volcanic ash. The volcanoes that produced this ash were located west and south of the Colorado Plateau, but the ash was transported by rivers and streams to be deposited where we find the Chinle Formation today.
 
purple-colored bentonite of the Chinle Formation

NPS photo

Bentonite muds within the Chinle often have a crumbly "popcorn texture" because they swell when wet and shrink when dry. This makes it hard for plants to grow, often leading to badlands-style scenery of bare purple, red, and gray slopes.

Outcrops of the Chinle Formation in Zion National Park can be found in the Kolob Canyons section, and in the southwestern part of the park near the Chinle Trail.
 
petrified wood in the Chinle Formation
Petrified tree trunk from the Chinle in Zion

NPS photo

The Chinle Formation is best known from Petrified Forest National Park, where massive petrified conifer tree trunks are found in abundance, as well as a wide assortment of animals, including early dinosaurs such as Coelophysis.


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Last updated: June 13, 2015

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