Geologic Provinces of the United States: Appalachian Highlands

Entrance to Delaware Water Gap.

Photo by Jack B Epstein, USGS.

The entrance to Delaware Water Gap National Recreation Area as viewed from atop Kittatinny Mountain, Pennsylvania on the right, New Jersey on the left. The Delaware River flows through the constricted gap behind us, and as it widens into the valley beyond and as its velocity lessens, it drops a streamlined bar, Arrow Island. Between the mountain, held up by Quartzites of the Silurian Shawangunk Formation, and the Precambrian metamorphic rocks of the New Jersey Highlands in the distance, is Wallkill Valley, underlain by Cambrian and Ordovician limestone and slate. The Recreation Area, in proximity to the New York-Philadlephia metropolitan complex, is the most heavily visited National Park facility in the eastern United States, attracting more than four million visitors a year.