Chinle Formation
The colorful Late Triassic badland floor beneath the Wingate cliffs — soft river-and-floodplain mudstones that hold the plateau's petrified wood and earliest dinosaurs.
Also known as: Chinle
Triassic — recovery, and the dawn of the dinosaurs
The world back then
Late Triassic, about 215 million years ago. This is a hot, muggy river plain near the equator — sluggish channels, oxbow lakes, and mudflats under a monsoon sky. Giant conifers topple and rot into the swamp, armored reptiles and the first dinosaurs work the banks, and the air hangs thick, buggy, and loud. Those rainbow colors are volcanic ash and rotting vegetation, chemically stained into the mud.
You, meanwhile, drift past the fossil version with a hat over your face — no monsoon, nothing with teeth in the shallows, no long wait to learn whether you survive the week. It's easy to forget, phone in hand at the take-out, that being a comfortable human wandering through deep time is a stroke of luck almost nobody in Earth's history ever got. The struggle's real — but so is the shade.
Recognize it in the field
- Typical color
- variegated — purple, gray, red-brown, greenish, and blue-gray
- Weathers as
- Slope-forming, colorful badlands; sandstone members (Shinarump, Moss Back) form local ledges and caprock. Its swelling clays undercut the cliffs above.
- Grain
- clay- and silt-dominated, locally conglomeratic (basal Shinarump)
Look for
- variegated purple/gray/red-brown badland slopes
- sits directly below the massive Wingate cliff
- petrified wood
- basal Shinarump conglomerate scoured into the Moenkopi
- bentonitic 'popcorn-weathering' swelling clays
How this rock was made
Low-relief tropical-to-subtropical river plains and lakes in the Late Triassic, fed by sediment shed from highlands to the south.
The setting: river (fluvial), lake-bottom (lacustrine), and marsh (palustrine) floodplains with minor wind-blown (eolian) input
Highly variable; thickens southward (a little over 1,710 ft / 520 m in the southern outcrops) and thins toward the plateau margins.
In the rock record
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Colorado Plateau
- Petrified Forest National Park (type area, Arizona)
- Capitol Reef National Park
- Canyonlands (slopes below the Wingate rim)
- San Rafael Swell (Temple Mountain)
- Glen Canyon
- Grand Staircase–Escalante
Float past it: Westwater Canyon · Meander Canyon · Stillwater Canyon · Cataract Canyon