The Delaware river gap was created about 3 million years ago when the mountain ridge holding back a 1000’ deep inland sea suddenly was breached. In a cataclysm of epic proportions, the sea roared through the gap and strew millions of tons of stone and gravel downstream to create the plateau silt formation that the city of Philadelphia is build on today. If you look on an aerial photo of the region, you can see the delta it created.
