The iconic fin of Seneca Rocks is the result of hundreds of millions of years of active geology. The rock itself is classified as Tuscarora quartzite (a metamorphic rock formed from pure quartz sandstone).
The events leading up to the creation of Seneca’s formation stretch back to the Silurian period, when multi-cellular life was just beginning to make its first forays into the terrestrial world. Flowering plants wouldn’t appear for another 300 million years. During this period, the sediments that would become sandstone, and finally quartzite, were being laid down at the eastern margin of a vast epicontinental sea known as the Iapetus Ocean. These sediments were themselves generated from the erosion of an ancient mountain chain. The Iapetus ceased to exist when all of the continental plates had joined to form Pangaea. At this time, the west coast of Africa was colliding with what is now the eastern coast of North America. This period of collision set up the Appalachian Orogeny (mountain building event). In their prime, the early Appalachians and Alleghenies rivaled what we see in the modern day Rockies. The tremendous pressure of continents colliding metamorphosed the pristine sandstone into the tremendously hard quartzite we know and love to climb.
The Appalachians and Alleghenies are an ancient range, and have been eroded down to more modest proportions. In fact, the mountain chain had been eroded to an almost completely flat plain by around 65 million years ago. Since that time, another deformation occurred. As the continent was uplifted, water began to once again cut through the remains of the Appalachians, carving the valleys that we see today. Seneca Rocks sits in the heart of the valley and ridge province of West Virginia. The folded nature of the bedrock is obvious when one considers that the once-horizontal strata of Seneca Rocks have been re-oriented vertically at one edge of an anticline which was once continuous with the rocks of North Fork mountain. Due to quartzite’s extreme hardness, it is highly resistant to erosion, and the Tuscarora formation serves as the spine of the remaining ridge lines. Seneca itself is the embodiment of one of these ridge lines, stripped of all softer and more easily eroded rock.