White Rim Sandstone
The white, resistant Permian bench of the Island in the Sky — a clean quartz sandstone caprock capped by the sub-Moenkopi unconformity.
Also known as: White Rim
Permian — vast deserts, ending in the worst extinction ever
The world back then
Early Permian, about 276 million years ago. A coastal dune-and-sabkha system rides the edge of a shallow sea — clean white sand piling into dunes, salty flats between, the sea washing in and out. Later, weird underground fluids will bleach the whole thing bone white. Hot, briny, half-desert half-shore, right at the water's edge.
That bleached sand is the white bench everybody drives, bikes, or wishes they'd trained for — and you drift far below it, doing none of the work. It took a coastal desert and some strange chemistry to build that rim; you just glide under it and look up. Comfortable and lucky, as usual.
Recognize it in the field
- Typical color
- white (bleached by hydrocarbon-rich fluids during diagenesis)
- Weathers as
- Hard, resistant caprock and bench-former — the namesake 'White Rim' bench, forming cliffs and caprock above the softer red Organ Rock.
- Grain
- fine-grained, well-sorted quartz sand
Look for
- white, cross-bedded, resistant quartz sandstone
- bench/rim geomorphology (the White Rim Road rides its top)
- eolian dune + interdune + sabkha facies
- sharp, resistant contrast over the red Organ Rock slopes
- capped by an unconformity beneath the Moenkopi
How this rock was made
A coastal dune and salty coastal flat (sabkha) system at the edge of an Early Permian sea, with alternating marine and nonmarine conditions during rising sea drowning the land (transgression).
The setting: coastal sand sea (erg) / marine-margin (dune, interdune, sabkha)
A thin, resistant cap that thins 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)
- the White Rim bench / White Rim Road (Island in the Sky)
- inner-gorge rims of the Green and Colorado Rivers
- Dead Horse Point overlook
- Elaterite Butte / Maze margins
Float past it: Cataract Canyon · Meander Canyon · Stillwater Canyon