Jesse Fried • Jul 10, 2017
The landform known as the Palisades is a long ridge that separates the Hudson River from the broad valley of the Hackensack River. The eastern edge of the Palisades is extremely steep. It contains miles of unbroken stretches of sheer cliff, up to several hundred feet tall, with talus slopes reaching down to the water's edge. The top of these cliffs is broad and flat. A mile or two to the west, the ridge slopes down steadily but not precipitously to the swamps of the meadowlands and the flat Piedmont in the middle of Bergen County.
The ridge's elevation increases gradually from south to north. It rises above the waterline at the Kill Van Kull, and forms the upland backbone of urban Hudson County, where it is called Bergen Hill. By the time it's directly across the Hudson River from the Spuyten Duyvel (the top of Manhattan Island), it reaches 300 feet and has extensive cliffs on its east face. The highest elevation it reaches in New Jersey is about 550 feet, though it gets somewhat higher across the border in Rockland County, NY.
Geologically, the Palisades are a Diabase sill - an underground flow of magma between flat layers of sedimentary rock. It was formed during the rifting that occurred as Pangea split up and the Atlantic Ocean began to open. The sill eventually tilted to dip to the west and was uplifted. The Hudson's channel marks a major geologic boundary between the highly deformed Paleozoic bedrock of Manhattan, the Bronx, and northward and the Cenozoic sedimentary basin of the Pidemont of Northeastern NJ, interspersed of course by igneous structures like the Palisades and the Watchung Mountains. The exact connection between this boundary and the location of the Palisades' striking cliffs continues to puzzle the author.
The southernmost twenty miles of the ridge are mostly urbanized, grading into suburban. In northern Bergen County, however, a decent portion of it is still forested. The observations that follow come from the Tenafly Nature Center. The ridge top has thin bedrock and is home to a dry mixed oak forest with blueberry in the understory, similar to upper slopes in the Highlands. Interspersed are little swamps containing black gum and red maple, with beech around them. These wet areas have a diversity of understory plants that I can't identify. Just off the top of the ridge, one encounters a lot of tulip poplar mixed in with the oaks, and notably holly as a minor component of the understory. The forest makes an interesting contrast with the nearby Watchung Mountains, which have similar bedrock and are of similar size and shape, just a little inland. Sweet gum and holly - both Southern species at the very top of their ranges - are absent from the Watchungs. One wonders if the difference is due to local climate. The Palisades, one imagines, have more of a coastal influence. Apparently Hemlock used to be common along streams, but has died out. I've also heard this about the Watchungs.
The way most people interact with the Palisades is by crossing them right before or after crossing the Hudson River. NJ Transit has tunnels through them, dating from the 19th century. The Pulaski Skyway, elevated above the Meadowlands, deposits motorists at the height of the ridge, where they descend into Jersey City and the Holland Tunnel. Route 495, the access road to the Lincoln Tunnel, ascends the western slope, and then dramatically spirals down the eastern face before entering the tunnel. The George Washington Bridge gains some of its iconic stature by being anchored at a high elevation on both sides of the river: to the top of the Palisades on the west side. The view from the GWB is a classic look at the Palisades - ignore the NYC skyline. The view of the Palisades is made all the more striking when the GWB is in the foreground.