Tag Archives: St. Peter Sandstone

GeoPic of The Week: Painted Bluff at Buffalo Point along the Buffalo National River

Painted Rock at Buffalo Point along the Buffalo National River.

Painted Bluff at Buffalo Point along the Buffalo National River

Painted Bluff gets its name from water seeping over the top portion of the bluff.  This darkens the rock giving it a painted look.  The rock formation that is painted is the St. Peter Sandstone.  The rock formation below the painted portion of the bluff is the Everton Formation.  Thin bedded limestone and dolostone layers make up the lower portion of the bluff.  The rock formations are both Ordovician (485-444 million years ago) in age, however there is an unconformity between the two formations.  An unconformity is a rock surface that represents a gap in the geologic record either due to a period of erosion or non-deposition.  Notice the wavy line halfway down the bluff.  This wavy line separates the sandstone from the limestone and is the unconformity surface.  The top of the limestone was at one time the rock exposed at the earth’s surface in this area.  The limestone was eroded, and then the sandstone was deposited upon it.