Catskill Mountain Prehistory

The Age of Fishes

During the Devonian Period (400 million years ago) high water levels caused large seas to cover much of Europe and North America. Known as the “Age of Fishes”, an abundance of sea life included the first amphibians, finned fish, mollusks and sharks. A HUGE inland sea covered the areas that are now the Rondout and Neversink watersheds. In this sea lived all types of prehistoric sea life.

watercolor painting of prehistoric fish

We learn about this prehistoric sea life through studying fossils. A fossil is the remains of an animal or plant turned into stone, or the impression of an organism preserved in rock. A fossil forms when soft tissues are broken down, leaving only hard parts such as teeth and bones. The bones become buried under layers of sediment, and are eventually replaced by minerals from groundwater. Movements of the surrounding terrain cause the rock holding the fossil to lift up, slowly making it way to the surface. The fossil is further exposed by weather and then possibly discovered and collected.

graphics showing fossil formation

How were the Catskill Mountains formed?

The Catskill Mountains formed, changed and formed again over millions of years:

  1. Huge rivers pushed sediments and rocks westward away from an eroding ancient mountain range.
  2. Pressure and time caused these sediments to become solid, creating sedimentary rock.
  3. Different rivers brought more sediment from other areas, covering this sedimentary rock.
  4. Tectonic plates pushing against each other lifted the rock to create a plateau.

Continuous water erosion of the exposed rocks is still creating the Catskill Mountains we see today.


Fun Fact! Did you know a meteor landed in the area? It did! During the Devonian Period, a meteor impact created a 7 mile-wide crater. The crater filled with sediment and through uplift and erosion became Panther Mountain. The impact is estimated to have occurred 375 million years ago, when much of what is now the Catskills was either river delta or a shallow sea. The crater lies 2,640 feet below the surface, is 7 miles wide, and lies directly under the mountain. The meteorite that struck is believed to have been roughly one-half mile wide, striking with a force equivalent to 11 trillion tons of TNT.

map showing panther mountain meteor impact footprint


During the Pleistocene Epoch (1.6 million years ago to 12,000 years ago) cold temperatures froze much of the water on earth. Snow covered the land and huge masses of slowly moving ice or glaciers extended over large areas. This time became known as the Ice Age.

Glaciers bulldoze sediment, dig out bedrock and move vast amounts of sediment great distances. Melting glaciers deposit sediment, rock and other materials and create very swift flowing streams and rivers and beautiful glacial lakes. A series of glaciers deposited much of the soil in the watershed areas. Some of these glaciers were as thick as two miles! 

If you would like to learn more about Catskill glaciers, check out our recorded webinar Glaciers of the Catskills by Hayley Springston of the Rondout-Neversink Stream Management Program.