Pictured Cliffs Sandstone
This unit is composed of primarily marine sandstone interbedded with thin layers of shale and is similar in composition, fossil assemblages, and depositional environment to the Intermediate unit of the Cliff House Sandstone. This unit is the youngest unit in the park and overlies the Lewis Shale. The Pictured Cliffs Sandstone represents the final regression of the Western Interior Seaway from northwestern New Mexico.
Did You Know?
The park considered a number of ideas for mitigating the damage that would be done if Threatening Rock fell. Proposed solutions included using dynamite to destroy it, anchoring it to the canyon wall with cables, or clearing out the rock debris behind it. It fell on January 22, 1941.