NJNew Jersey Geography

New Jersey touches dry land in only one direction. The Hudson River, the Kill Van Kull, the Arthur Kill and Raritan Bay wrap the northeast; the Atlantic runs down the east; Delaware Bay and the Delaware River close off the entire west. The only land boundary is the 48-mile line with New York, surveyed in 1774 between a fixed point on the Hudson and another on the Delaware. Everything else is water, which comes close to making New Jersey an island and explains why so much of its history is bridges, tunnels and ferries.

Inside that outline sit about 9.3 million people on 8,723 square miles, 47th in area and first in density at well over 1,200 people per square mile. New Jersey is also the only state where every single county is counted as part of a metropolitan area.

Four provinces in seventy miles

From High Point in the northwest corner to Sandy Hook is about seventy miles in a straight line, and in that distance the ground passes through four separate physiographic provinces.

• Valley and Ridge. The northwest corner, folded Palaeozoic sedimentary rock belonging to the same Appalachian belt that continues to Alabama. High Point, 1,803 feet, sits on the Kittatinny Ridge, with the long Kittatinny Valley below it.
• Highlands. A belt of Precambrian gneiss ten to twenty miles wide running southwest to northeast, geologically continuous with the Hudson Highlands and the Reading Prong. Its magnetite ore fed forges that supplied the Continental Army.
• Piedmont. The Newark Basin, a Triassic rift valley of red sandstone and shale shot through with diabase intrusions. The Palisades and the three Watchung ridges are both products of that rifting.
• Atlantic Coastal Plain. Around three fifths of the state, loose sand, clay and greensand marl dipping gently seaward, none of it older than roughly 130 million years.

The Fall Line, where the hard Piedmont rock meets the soft coastal plain sediments, runs from Trenton northeast through New Brunswick toward Perth Amboy. Trenton is the capital because it stands on that line, at the head of navigation on the Delaware, the furthest inland a seagoing vessel could reach.

The line where the ice stopped

About 21,000 years ago the Wisconsin ice sheet halted in New Jersey and dropped its load along a terminal moraine that runs from Perth Amboy northwest through Morristown, Denville and Hackettstown to Belvidere on the Delaware. North of that line the landscape is scoured bedrock, thin soil, kettle ponds and lakes. South of it the ground was never glaciated and has weathered deeply for millions of years.

Behind the ice, Glacial Lake Passaic filled the Piedmont basin, roughly thirty miles long, ten wide and 240 feet deep, penned in by the Watchung ridges. When it finally drained through Little Falls it left flat lake-bottom ground that survives as the Great Swamp, Troy Meadows and the Hackensack Meadowlands.

The Palisades are older by far, a sheet of diabase forced between sedimentary layers about 200 million years ago and later exposed as cliffs 300 to 550 feet high along twenty miles of the Hudson. Commercial quarrying was eating them until New York and New Jersey jointly created the Palisades Interstate Park Commission in 1900. Downstream on the Passaic, the Great Falls drop 77 feet over a Watchung basalt ledge, the site Alexander Hamilton chose in 1791 for the first planned industrial city in the country.

The Pine Barrens and the water beneath them

The Pinelands cover about 1.1 million acres, close to 22 percent of New Jersey's land area, and form the largest undeveloped tract on the eastern seaboard between Boston and Richmond. It survived because the soil is almost pure sand, acidic and starved of nutrients, so nobody could farm it. Pitch pine and scrub oak took it instead, and fire runs the system: pitch pine resprouts directly from its scorched trunk, which very few conifers can do.

Underneath sits the Kirkwood-Cohansey aquifer, holding an estimated 17 trillion gallons of fresh water. The sand is so permeable that rain sinks almost immediately, so the streams are fed by groundwater rather than runoff. They hold a steady temperature year round and run the colour of strong tea, stained by cedar tannins and dissolved bog iron. Congress designated the area the first National Reserve in the United States in 1978. The same sandy, acidic ground supports the state's cranberry bogs, and the cultivated highbush blueberry was bred at Whitesbog in 1916.

A shoreline that will not hold still

New Jersey's 130 miles of Atlantic shore are almost entirely barrier islands and spits, separated from the mainland by shallow back bays including Barnegat Bay and Great Bay, and the whole chain migrates.

The net drift of sand along the northern shore runs northward, which is why Sandy Hook is a six-mile spit steadily extending toward New York Harbor rather than a fixed headland. Inlets shift too: the original Barnegat lighthouse, built in 1835, was undermined as the inlet moved and collapsed into the sea in 1856.

Cape May Point, at roughly 38 degrees 56 minutes north, lies south of both the Mason-Dixon Line and the city of Baltimore. Offshore, the Hudson Canyon cuts across the continental shelf for about 400 miles, the largest submarine canyon on the eastern seaboard, carved when sea level was hundreds of feet lower and the Hudson emptied at the shelf edge.

Boundaries settled in court

Water borders make for long arguments. The New York line was disputed for nearly a century before the 1774 survey fixed it, and the two states were still in court over the Hudson in the 1990s. In New Jersey v. New York, decided in 1998, the Supreme Court ruled that the original three acres of Ellis Island belong to New York but the roughly 24 acres of landfill added around it belong to New Jersey, so a single national monument now sits in two states.

The Delaware boundary is more lopsided. Within the twelve-mile circle drawn around New Castle, the line runs along the low-water mark on the New Jersey shore, which means Delaware owns the riverbed right up to New Jersey's beach. The Supreme Court reaffirmed that in New Jersey v. Delaware in 2008, letting Delaware block a liquefied natural gas terminal that New Jersey wanted built on its own bank. Upstream, the Delaware runs 330 miles without a single dam on its main stem, the longest undammed river east of the Mississippi.

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