Geology of the Pryor Mountains

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The geologic history of the Pryor Mountains begins much the same way the story of the Beartooth Mountains does.  The Pryor Mountains are also underlain by ancient granites and gneisses that date back 3.0 – 4.0 billion years.  The same seas that deposited the sedimentary rocks in the Beartooths covered the ancestral Pryors and deposited the same types of rocks.  Specific rock units and thicknesses are displayed in the stratigraphic column.   The Pryor Mountains were uplifted in a similar style during the Laramide Orogeny.  This is where the similarities in the stories end. 

The Pryor Mountains receive far less precipitation than the Beartooths and were not glaciated.  Therefore, the striking glacial features found in the Beartooths are not present in the Pryors.  The overlying sedimentary rocks of the Pryor Mountains are still visible today (Pryor Mtn limestone, Crooked Creek Rd).  The underlying granites and gneisses are limited in outcrop, unlike the Beartooths. 

Unlike the Beartooths, the Pryor Mountains are known for their spectacular caves (stalactite formation, big ice cave, cave ice crystals).  Pryor Mountain caves form in the Madison limestone.  Limestone is a rock that dissolves easily.  Precipitation is concentrated along cracks in the limestone and gradually dissolves it until the cracks transform into the caves that we see today.