Aerial view of the Delaware Water Gap, Appalachian Mountains of Pennsylvania. From the air the structural origin of the ridges and valleys can be clearly seen and having about the same elevation, the ridges are refered to as even-crested ridges. The area exhibits examples of both accordant drainage and discordant drainage.
These folded Paleozoic rock layers at Eagle Rock, Virginia are part of a large syncline and illustrate the deformation that has taken place in the Appalachian Mountains.