Organ Rock Formation
The dark-red Permian river-plain siltstone below the White Rim — recessive red slopes that locally stand up as the pinnacles of the Land of Standing Rocks.
Also known as: Organ Rock, Organ Rock Shale
Permian — vast deserts, ending in the worst extinction ever
The world back then
Early Permian, about 287 million years ago. Braided rivers drag dark-red silt off a dying mountain range across a wide, dry basin — flash floods, dust, red mud, and the odd wandering dune. Hot and stark, a red-bed apron baking under the Permian sun. Not a soul, just red earth moving downhill.
Now it's the red slope below the White Rim, and you ride a steady current past a country that was all dust and flash flood. It shed itself off a dying mountain in violent fits; you drift through the calm aftermath. The warm animal with the good seat wins again.
Recognize it in the field
- Typical color
- dark red to reddish-brown
- Weathers as
- Chiefly a slope-former — recessive dark-red slopes below the White Rim bench; locally forms vertical cliffs and pinnacles (Land of Standing Rocks, Chocolate Drops) where indurated and White-Rim-capped.
- Grain
- silt to fine sand; thinly bedded
Look for
- dark-red thin bedding
- siltstone–sandstone–conglomerate cycles
- recessive, slope-forming weathering
- White-Rim-capped pinnacles (Standing Rocks)
- braided-fluvial channel and floodplain structures
How this rock was made
A distal-river (fluvial) red-bed apron shed from the ancestral Uncompahgre highland across the Permian basin.
The setting: braided river channels, floodplains, and localized ergs
~500 ft (Monument Valley, Stewart 1959); 0–800+ ft (Condon 1992). Thins/pinches out eastward.
In the rock record
Part of the Cutler Group.
↑ Younger — rests above
↓ Older — sits beneath
Where to see it
Regions: Colorado Plateau (Paradox Basin margin)
- Land of Standing Rocks / Chocolate Drops (Maze District)
- red slopes beneath the White Rim throughout Island in the Sky
- Monument Valley (type area)
Float past it: Cataract Canyon · Meander Canyon · Narrow Canyon