History of the Great Swamp

Credit: Kristina Necovska

A watershed is a geographical area, in which all of the streams flow into a single body of water. The Great Swamp watershed covers nearly 35,000 acres and is located within Morris and Somerset Counties, and includes portions of ten different towns: Bernardsville, Bernards Township, Chatham Township, Harding Township, Long Hill Township, Madison Borough, Mendham Borough, Mendham Township, Morristown, and Morris Township. The Great Swamp National Wildlife Refuge takes up nearly 25% of the watershed.

Geological History

New Jersey’s Great Swamp is nestled within a 55-square-mile natural basin, about 25 miles from New York City. It is a quiet, undisturbed place today, but it wasn’t always that way.

Millions of years ago, the continent of Africa collided violently with North America, pushing up great mountains to the north and west. Erosion has since cut them down to size. When Africa broke away, hot molten rock flowed up from the earth’s interior, creating the Watchung Mountains to the south and east. Again, erosion has taken its toll.

About 18,000 years ago, the Wisconsin Glacier began to cease its southerly motion and melt, leaving behind a great pile of rock and soil along a line from Chatham to Morristown.

As the last parts of the glacier receded 16,000 years ago, it formed the basin of the Great Swamp. Halted by the Watchung Mountains, the glacier left behind another great pile of earth and rocks to the west of the Great Swamp basin. Today, that pile is known as Basking Ridge.

After the glacier began to recede, the melt-off formed Glacial Lake Passaic. This massive lake had a depth of nearly 300 feet and was 30 miles long and 5-10 miles wide. Eventually the water pressure forced a gap through Long Hill and formed the Millington Gorge and the Passaic River. The lake nearly drained, leaving behind a basin that we know as the Great Swamp today. 

Natural History

Though called a swamp, the Great Swamp National Wildlife Refuge and adjoining public lands encompass a great variety of other habitats as well: grasslands, sandy knolls, ponds, brooks, marshes, woodlands, and ridges. In this rich mix, Great Swamp displays plants from both southern and northern zones, including 215 species of wildflowers.

The varied vegetation provides a diversity of homes for the 220 bird, 33 mammal, and many reptile, amphibian, and fish species in Great Swamp. Of these species, 26 are listed by the state of New Jersey as threatened or endangered. The Great Swamp is also home to one of the state’s largest breeding populations of Eastern Bluebirds, and it boasts a thriving Great Blue Heron rookery, which hatches about 80 chicks each summer.

Human History

There is evidence that humans lived in the Great Swamp as early as 12,000 years ago, when mastodon and giant beaver still inhabited the area. When the first Europeans arrived in the 1600s, they encountered a group of Native Americans who called themselves the Lenape, which means “original people”. For a time, the two groups lived peacefully together, but disease and pressures for the land eventually forced the Lenape to abandon their home. The European settlers built small towns and villages, many of which remain today: Green Village, New Vernon, Basking Ridge, Meyersville, and others.

The Great Swamp Watershed figured prominently in the Revolutionary War. Continental Army troops spent eight years in the Watershed and George Washington wintered here twice. Its high western rim provided a strategic lookout to the east and New York City, where the British troops were quartered.

In the 19th century, area residents logged the forests of Great Swamp for firewood and building materials, and tried with limited success to drain the marshlands for farming. Also during this time, the area became a retreat for wealthy New Yorkers, who built great estates in and around the watershed.

The Battle against the Port Authority

The 20th century saw the unveiling of the most ambitious plan to put Great Swamp to human use. In 1959, the Port Authority of New York proposed to build an international jetport in the swamp, with four 10,000-foot runways. The proposal would have bulldozed many of the hills, filled in the swamp, and demolished 700 homes and other structures.

For four years, local residents fought the plan — and finally won. Thanks to their acquisitions of swampland, the Great Swamp became a National Wildlife Refuge in 1964. The jetport plan was abandoned in 1968 when part of the Refuge became a Federal Wilderness Area. Today, the 7,500-acre National Wildlife Refuge is the crown jewel in a remarkable array of protected areas in the Great Swamp Watershed.