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

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The Fox Hills Formation

Fox Hills Formation

Concretions in Fox Hills sandstone along Rooney Road.

The Fox Hills Formation

The retreating sea...

Fossil plants are present in concretions, balls of sandstone surrounding an organic core, found in the Fox Hills sandstone.  The barrier islands and lagoons which formed seem to have been large enough to support land-based plants.

How the plants arrived or began their colonization is not known.  Some may have spread from adjoining regions, moving east as the sea retreated.  Others may have been carried by the winds, picked up as seeds to somehow land on a newly-emerging island   Still others may have survived among wood debris from a distant forest, dislodged by a violent storm, to be swept out to sea by ocean currents and deposited on shore.