Delaware Water Gap: The River That Split a Mountain

The gap you're passing through is one of the most dramatic geological accidents in the eastern United States. Here, the Delaware River has cut straight through Kittatinny Ridge, a long spine of the Appalachian Mountains made of some of the hardest rock on the continent, quartzite and conglomerate that formed roughly five hundred million years ago when quartz pebbles accumulated at the bottom of a shallow sea. By any reasonable geological logic, a river should not be able to punch a hole through such rock. The Delaware did it anyway.

The explanation lies in the age of the river relative to the mountains. The Delaware was flowing long before the ridge was pushed up to its present height by continental collision, roughly four hundred million years ago. As the land rose, the river simply kept cutting downward, maintaining its course even as the mountain climbed around it. The Wisconsin glacier, which blanketed this entire area about twenty-one thousand years ago, scoured the gap into its present dramatic shape when it retreated.

The Lenape people called the river Lenapewihittuk, the river of the Lenape, and traveled through this gap for thousands of years. European settlers found it nearly impassable until a road was built on the Pennsylvania side in seventeen ninety-three.

Once the road came, and then the railroad in the eighteen thirties, the gap became one of the most fashionable resort destinations on the East Coast. The Kittatinny Hotel opened in eighteen thirty-two with just twenty-five guests; within decades the area was hosting more than sixteen hotels and drawing visitors from Philadelphia and New York who came to hike the ridge, fish the river, and simply stare at the scenery.

Today the surrounding land is protected as the Delaware Water Gap National Recreation Area, preserving seventy thousand acres of forest, river, and ridge along the Pennsylvania-New Jersey border.