The Pennsylvania Salient is a geological region which is very obvious to identify if you look from the sky. It is the curve in the Appalachian Mountain Range (see satellite image). The bend begins in southern New York and northeastern Pennsylvania and extends across Pennsylvania to the border of Maryland. In this area, the ridges of the Appalachians turn from a roughly north-south orientation to an east-west orientation and then north-south again. Scientists argued that an underground mass of dense, mafic volcanic rock beneath the bend forced the mountain chain to shift as it formed hundreds of millions of years ago. As the North American and African plates collided, the North American plate began to fold and thrust upward. However, the mass of volcanic rock became a barrier and forced the mountains to push up around it.