Coconino Sandstone
The pale, cross-bedded Permian dune sandstone that forms the Grand Canyon's bold white cliff — a fossil desert printed with reptile tracks.
Also known as: Coconino
Permian — vast deserts, ending in the worst extinction ever
The world back then
Permian, about 280 million years ago. This is pure desert — a Sahara-sized sea of white dunes with no ocean anywhere near, the sand so clean and wind-sorted it squeaks. Blistering, dry, and nearly lifeless; the only tracks are little reptiles scrambling up the dune faces. Just white sand and hot wind to the curve of the earth.
Now it's a bright white cliff a thousand feet overhead, and you're loafing in its shade watching it drift by. No dunes to cross, no thirst to ration — the boat does the walking. Loafing under a fossilized Sahara is a deal almost nobody in the history of life was offered.
Recognize it in the field
- Typical color
- white to tan (brown/red in western Grand Canyon)
- Weathers as
- Prominent cliff-former — a bold, sheer white cliff high on the canyon wall.
- Grain
- fine-grained, well-sorted, frosted and rounded
Look for
- large-scale planar eolian cross-bedding (frozen dune faces)
- frosted, well-rounded, well-sorted wind-worked sand
- reptile and arthropod trackways (no marine fossils)
- thickens eastward, thins to nothing in the far west
How this rock was made
A vast Permian sand sea at the edge of the world; no marine influence.
The setting: wind-blown desert dune field (erg)
~700 ft east, thinning westward; ~57 ft minimum.
In the rock record
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Grand Canyon / Colorado Plateau
- the white cliff throughout the Grand Canyon (thickest east/central)
- Aubrey Cliffs (type section)
Float past it: Grand Canyon