Paradox Formation
The buried Pennsylvanian salt of the Paradox Basin — the evaporite whose slow tectonics raise anticlines, collapse valleys, and steepen Cataract Canyon.
Also known as: Paradox
Pennsylvanian — the great coal swamps
The world back then
Pennsylvanian, about 308 million years ago. Picture a fault-bounded basin behind a reef barrier, the sea sneaking in and getting trapped, then evaporating down to blinding salt flats under a brutal sun — then flooding again to drop black, stinking mud. Sea, salt, sea, salt, dozens of times. Hot, briny, and airless, the whole basin cooking down to crystal.
That buried salt still moves — slowly, flowing like putty, shoving up the anticlines around Moab and steepening the very rapids ahead of you. You drift over the trapped ghost of an evaporated sea while it does the heavy lifting underground. Lucky, comfortable, and slightly outmatched by a rock.
Recognize it in the field
- Typical color
- gray carbonates, white-to-gray gypsum, black shale
- Weathers as
- Incompetent and recessive — rarely a cliff; where exposed it is contorted and brecciated. Its plastic flow drives salt tectonics: anticlines, salt-collapse valleys, grabens, and the doming of overlying rock.
- Grain
- crystalline evaporite; fine clastic shale/siltstone
Look for
- cyclic evaporites (up to ~29 evaporite–carbonate cycles)
- thick bedded halite in the subsurface
- outcrop mostly gypsum with broken chunks of limestone/sandstone/shale (flowage breccia)
- contorted, folded, and brecciated bedding from salt flowage
- euxinic black shales at flooding highstands
- exposed only along the crests of anticlines and domes
How this rock was made
A fault-bounded basin (~150 × 80 mi) behind a shelf/reef barrier, with cyclic seawater restriction and evaporation alternating with marine flooding (black shale).
The setting: restricted evaporating-sea deposit (evaporite) basin
Highly variable due to salt flowage: ~2,000 ft outcrop average, ~4,000–6,000 ft subsurface, locally >12,000 ft (present thickness, flowage-thickened); ~7,000 ft maximum depositional.
In the rock record
Part of the Hermosa Group.
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Colorado Plateau (Paradox Basin)
- Paradox Valley, Colorado (namesake)
- crests of salt anticlines (Onion Creek, Moab, Fisher)
- river-level pockets in Cataract Canyon (oldest exposed rock in Canyonlands)
Float past it: Cataract Canyon