A Geological Tour of Denver, Golden, and Colorado's Front Range

Pericles Press Home | Book | Contact Us/Ordering

A Theory | Seven Nations | Governments and Empires | Geological Past

Geologic Time Period

The Pierre Shale Formation

Pierre Shale on Rooney Road

Pierre Shale - Jagged exposure of shale with red pigmentation along Rooney Road.

The Pierre Shale

Not all of the Pierre Shale dissolves easily or quickly into mud. In places, chemical or geological conditions combined to produce a case-hardened texture more resistant to time and the elements. A reddish crust, suggestive of an iron presence, may have contributed to an erosion-resistant formation, simply been a by-product of conditions, or may have been a pigment produced by an algae-like organism. A relatively thick toughened layer may also suggest a long-term presence of organisms capable of using calcium to produce shells, leaving a calcite (calcium carbonate) limestone.