San Rafael Group
The Middle Jurassic marine-and-sandstone package between the Navajo and the Morrison — Carmel, Entrada, Curtis, and Summerville, the arch-building middle of canyon country.
Also known as: San Rafael
Jurassic — the golden age of dinosaurs
The world back then
Middle Jurassic, roughly 165 million years ago. A shallow sea keeps advancing and retreating across the region — flooding to lay marine mud and lime, drying to dunes and salty flats, then flooding again. Four rounds of it, wet to dry and back. Hazy, briny, half-desert half-shore, the coastline restless for millions of years.
That indecisive coastline is the Carmel-through-Summerville stack, arch-building Entrada and all, and you cross the whole saga in an afternoon. The sea couldn't commit for millions of years; you don't have to. Comfortable, warm, and unbothered by any of it — the human superpower.
Recognize it in the field
- Typical color
- red, white, gray, green, and chocolate (varies by member formation)
- Weathers as
- A mixed cliff-slope package: the Entrada builds fins and arches, the Curtis caps ledges, and the Carmel and Summerville form banded slopes.
Look for
- four-formation Middle Jurassic marine-eolian-tidal succession
- records repeated advance/retreat of the Sundance/Carmel seaway
- the arch-building Entrada is its signature unit
- stands fully exposed in the San Rafael Swell
How this rock was made
Repeated Middle Jurassic advances and retreats of the Sundance/Carmel seaway across the Colorado Plateau.
The setting: mixed marine, wind-blown (eolian), tidal-flat, and salty coastal flat (sabkha)
A composite of its member formations; no single stated group thickness.
In the rock record
↑ Younger — rests above
↓ Older — sits beneath