Entrada Sandstone

The Entrada Sandstone is a Middle Jurassic geologic formation within the San Rafael Group, found across Wyoming, Colorado, northwest New Mexico, northeast Arizona and southeast Utah, mainly on the Colorado Plateau, dating to the early-to-middle Callovian stage. It consists of fluvial mudstone, siltstone and eolian sandstone deposited in varied settings including tidal mudflats, beaches and sand dunes within a broader desert of sand seas surrounding the shallow Sundance Sea, and it reaches 314 meters thick at its Kaiparowits Basin reference section, dividing there into three informal members of differing color and lithology. In its type section the formation is red silty sandstone with interbedded mudstone, while farther south and east it becomes cliff-forming red or white crossbedded sandstone, including a distinctive white slickrock facies attributed to bleaching by organic-rich fluids from overlying beds.