Uinta Formation
The drab-to-reddish Eocene river beds that cap the Uinta Basin — type unit of the Uintan mammal age, the rim above Desolation Canyon.
Also known as: Uinta
Paleogene — mammals take over after the dinosaurs
The world back then
Late Eocene, about 44 million years ago. The great lake is shrinking, and rivers are rebuilding floodplains over its old bed — drab, muddy channels wandering a warming plain, strange early mammals in the brush, the rhino-sized Uintatherium among them. Green, buggy, and low, the last chapter of the basin filling in. Not scenic; just busy.
Now it's the drab rim high above Desolation, and you drift far below it, un-hunted and unhurried. Those floodplains were thick with strange beasts; your river just carries you and lets you crane your neck. Comfortable, safe, and a good 44 million years late — the ideal way to visit.
Recognize it in the field
- Typical color
- drab gray-green to reddish
- Weathers as
- Slope- and cliff-forming fluvial sandstone and mudstone — the upper walls and rim above Desolation Canyon.
- Grain
- sand to mud, lenticular
Look for
- drab-to-reddish fluvial sandstone and mudstone
- the top of the Uinta Basin Tertiary fill
- classic Eocene mammal badlands
- type unit of the Uintan land-mammal age
How this rock was made
Rivers and floodplains rebuilding over the shrinking Lake Uinta in the late Eocene.
The setting: river (fluvial) floodplain
Up to ~1,500-3,000 ft regionally.
In the rock record
↓ Older — sits beneath
Where to see it
Regions: Uinta Basin (Colorado Plateaus province)
- the upper walls and rim above Desolation Canyon (Green River, Uinta Basin)
Float past it: Desolation Canyon · Gray Canyon