صفيحة أمريكا الشمالية
Like the rest of this part of the Appalachian Mountains, Spruce Knob began to form with the breakup of Pangea I between 570 and 500 mya. The African Plate separated from the North American Plate opening the Proto-Atlantic Ocean. The North American Plate stretched and thinned, allowing it to backfill with a shallow inland sea. About 50 million years later, with the Taconic Orogeny, the two plates reversed course and began to move towards each other. Mid-ocean subduction created a volcanic arc (now known as the Blue Ridge Mountains) which eventually collided with the North American Plate. The arc fused onto the continent and the land to the west was uplifted.