The geological process responsible for the formation of the Appalachian Mountains is Plate tectonics and continental collision.

The Appalachians were formed over millions of years through the collision of tectonic plates, particularly during the formation of the supercontinent Pangaea. This collision caused the Earth's crust to fold, uplift, and fracture, creating the mountain range. The initial formation occurred around 480 million years ago, and subsequent geological activity, including erosion and sedimentation, further shaped the mountains into their current form. This complex geological history has contributed to the diverse landscapes and ecosystems found within the Appalachian region today.