Book Cliffs
A 250-mile Cretaceous escarpment — Mesaverde shoreline sandstone and coal over Mancos badlands — and the world's textbook exposure of an ancient retreating seaway.
Also known as: the Book Cliffs
The Book Cliffs are a ragged, banded escarpment that runs some 250 miles from near Helper, Utah to Grand Junction, Colorado — often called the longest continuous cliff line in the world. The cliffs are cut into the Late Cretaceous Mesaverde Group: stacked shoreline sandstones and black coal seams standing above the soft gray badlands of the Mancos Shale. Because those layers record a shoreline of the Western Interior Seaway advancing and retreating, the Book Cliffs are the world's textbook exposure of ancient beaches, deltas, and coal swamps — geologists come from everywhere to walk them.
Geology
Formation: An erosional escarpment cut into the Late Cretaceous Mesaverde Group and underlying Mancos Shale — a regressive clastic wedge shed east off the Sevier mountains into the Western Interior Seaway — now retreating northward as the soft Mancos undermines the resistant sandstone cliffs.
The Book Cliffs are the global type example for sequence stratigraphy of a shoreline: the lateral pinchout of Mesaverde sandstones into the Mancos Shale is exposed continuously for hundreds of miles and is studied worldwide as a model for shallow-marine reservoirs.
Primary formation: Mesaverde Group
Age: Cretaceous (80 Mya)
Named for the resemblance of the vertical cliff faces to a shelf of books.
History
Named for the cliffs' resemblance to a shelf of standing books.
Long a major coal-mining district (the Blackhawk Formation coals).