Hatfield Swamp

Hatfield Swamp is a fresh water wetland area in the US state of New Jersey, forming what might be considered the "second bank" of the Passaic River between Morris and Essex counties.

During the late Triassic and early Jurassic periods, when the North American plate separated from the African plate, an aborted rift system was created. The resulting rift valley, known as the Newark Basin, was filled with alternating layers of red bed sediment and flood basalts. Over millions of years, the rift valley was faulted, tilted, and eroded, until the edges of the hard flood basalt layers formed ridges. Prior to 20,000 years before the present, an ancestral Passaic River flowed through a gap in these ridges. This changed when the Wisconsin Glacier, a massive continental ice sheet which formed during the last ice age, advanced on the region and permanently plugged the gap with glacial rubble. As the glacier eventually melted back, water pooled behind the ridges (known today as the Watchung Mountains), forming Glacial Lake Passaic. After thousands of years, the lake drained leaving behind many swamps with various hardwood trees struggling to take hold, including the Hatfield Swamp.

The Whippany River flows into the Rockaway River, at the western end of the swamp. The Rockaway River travels a short distance and then flows into the Passaic River near the center of the swamp. The USGS gaging station is 1.3 miles (2.1 km) downstream of the Rockaway River confluence. At this point the Passaic River drainage is three hundred forty nine square miles. This includes the Rockaway River drainage of one hundred twenty five square miles and the Whippany River drainage of sixty nine square miles.

The area is from 180 feet (55 m) above sea level to 160 feet (49 m). Latitude 40.85 N and Longitude 74.32 W

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