Park City Formation
The cherty, fossil-rich Permian limestone that caps the Weber cliff in the Uinta canyons — the last Paleozoic sea before the red Triassic beds.
Also known as: Park City
Permian — vast deserts, ending in the worst extinction ever
The world back then
Permian, about 274 million years ago. A shallow sea laps a low coast — tidal flats and salty crusts to the east, a lime-and-chert shelf to the west, cherty and fossil-rich. Out west it's the same rock they mine for phosphate. Warm, shallow, and briny, the last sea before the whole place goes red and Triassic.
Now it's the gray cap on the big Weber cliff, the Paleozoic's closing rock, and you drift past it into the mellow sequel. That was the last shallow sea before everything turned red and Triassic; you get the breathable epilogue. Being the comfortable creature who arrives right at closing time — that's the move.
Recognize it in the field
- Typical color
- light gray to pinkish
- Weathers as
- Ledge- and slope-forming mixed carbonate-clastic.
- Grain
- fine, calcareous
Look for
- cherty, fossiliferous gray-to-pinkish limestone
- limy and cherty sandstone with shale
- equivalent to the phosphate-rich Phosphoria Formation
- the last Paleozoic marine unit before the red Triassic
How this rock was made
A Permian gently-sloping lime seafloor (carbonate ramp) that intertongued westward with the phosphatic Phosphoria.
The setting: shallow marine (tidal flats/sabkha eastward to carbonate shelf westward)
~30 m (east) to ~300 m (west) regionally.
In the rock record
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Uinta Mountains (Middle Rocky Mountains province; NPS files Dinosaur NM under Colorado Plateaus)
- the top of the Paleozoic section in the Uinta canyons (Split Mountain)
Float past it: Split Mountain · Whirlpool Canyon