Wasatch Formation
The variegated red-and-gray Paleocene-Eocene river beds at the base of the Uinta Basin Tertiary — the lower walls of Desolation Canyon, mapped as the Colton where it reddens.
Also known as: Wasatch, Colton Formation
Paleogene — mammals take over after the dinosaurs
The world back then
Paleocene to Early Eocene, about 53 million years ago. Rivers and floodplains sprawl around the edge of a growing lake system — variegated red, purple, and gray mud, sluggish streams, the odd early mammal picking through the brush. Warm, wet, and low, the basin filling up right before the great lake spreads over it. A muddy prelude.
Now it's the banded lower walls of Desolation Canyon, and you drift past floodplains that were headed for the bottom of a lake. You get the dry, breathable, look-around version they never did. The comfortable seat at the good end of deep time — yours again, for almost nothing.
Recognize it in the field
- Typical color
- variegated red, purple, and gray
- Weathers as
- Slope- and badland-forming variegated mudstone with sandstone ledges — the lower walls of Desolation Canyon.
- Grain
- mud to sand, lenticular
Look for
- variegated red-purple-gray fluvial mudstone
- lenticular channel sandstones and conglomerate
- the base of the Uinta Basin Tertiary section
- mapped as the Colton Formation where it reddens
How this rock was made
Streams and floodplains around the margin of the Eocene lake system before and during the spread of Lake Uinta.
The setting: river (fluvial) floodplain (alluvial)
Highly variable across the basin.
In the rock record
↑ Younger — rests above
Where to see it
Regions: Uinta Basin (Colorado Plateaus province)
- the lower walls of Desolation Canyon (Green River, Uinta Basin)
Float past it: Desolation Canyon · Gray Canyon · Uintah Basin