Natural History

The Setting for the Raritan Headwaters Region
Map of the Raritan River Watershed Headwaters Region

The Raritan Headwaters Region

The Raritan Headwaters region is located in north-central New Jersey and is defined by the area of land that drains into the North and South Branches of the Raritan River. The region contains the headwaters of the Raritan, the river which drains to the Raritan Bay and Atlantic Ocean. The drainage basin of the Raritan River covers approximately 1,100 square miles, making it the largest river basin located entirely within the State of New Jersey. The South Branch of the Raritan River is 51 miles long from its source in Budd Lake to its confluence with the North Branch in Branchburg. The North Branch of the Raritan River originates as a spring-fed stream in Morris County and flows south for approximately 23 miles to its confluence with the South Branch. Our watershed covers 470 square miles in three counties: Morris, Hunterdon, and Somerset. It includes all or portions of 39 municipalities.

The Raritan Headwaters region provides clean water to approximately 1.5 million people in central New Jersey including drinking water, irrigation water for farms, nurseries and golf courses and process water for industries. In addition, our watershed is used for many recreational activities including boating, fishing, golf and hiking, and provides habitat for many aquatic and terrestrial organisms, including many rare plants and animals. The Raritan Headwaters contains a larger percentage of forested area than the Lower Raritan River Basin and the Stony Brook-Millstone Watershed.

The northern half of the watershed is characterized by the Highlands physiographic province, which reaches elevations of approximately 1,400 feet in some areas. Ridges associated with these elevations were formed from hard rock material that resisted erosion, while valleys in the lower elevations are comprised of softer materials — limestone and shale. Soils of this region are moderately well-drained and have moderate infiltration rates. Limestone and glacial aquifers of the Highlands contribute to this watershed’s moderate to high infiltration rates.

The southern half of our watershed is characterized by the Piedmont physiographic province with its gently rolling terrain and unique soil profile.


The topography of the Raritan Headwaters ranges from 47 feet above mean sea level (msl) at the confluence of the North and South Branches in Branchburg to elevations of approximately 1,400 feet near Budd Lake in the headwater areas of Morris County. Some of the highest elevations in the State occur in the Highlands because the Precambrian rocks on many Highlands ridgelines are resistant to erosion.

Raritan Headwaters Topography Map

The watershed lies in two physiographic provinces. The higher altitude northern section is in the Highlands. A portion in the north was glaciated in the last ice age and contains the Wisconsin terminal moraine. Overall, the bulk of the Highlands is un-glaciated and contains deep soils with good recharge characteristics. These soils overlie Precambrian crystalline rocks that are highly weathered and fractured in many locations. In these situations, recharge, storage and transmission of groundwater are good. However in some locations the bedrock is massive and un-fractured, leading to relatively poor aquifer conditions. The largest expanses of forests of better quality lie in the un-glaciated Highlands.

At the southern end of the Highlands in the Borough of Peapack-Gladstone, a small area of limestone of Cambrian age is present. This formation is a prolific aquifer due to its extreme degree of weathering. It is overlain by soils weathered from the bedrock material that are only moderately permeable but are also excellent agricultural soils.

The topographically lower southern portion of the watershed lies in the Piedmont province. The underlying geology consists of red shale, siltstones and mudstones of Triassic age. In several locations basalt and diabase intrusions are present. Known as the “Newark Basin” or the “Brunswick Formation,” soils in this area are dominated by high percentages of fine clay particles and thus produce large amounts of run-off. This tendency has been aggravated by approximately 300 years of agricultural activity and recent suburban development.

More detailed information on the geology, soils, vegetation, and wildlife of our watershed follows. This information is taken from Setting of the Raritan River Basin: A Technical Report for the Raritan Basin Watershed Management Project, published by the New Jersey Water Supply Authority in July 2000. The Raritan Headwaters Association is a member of the Raritan Basin Watershed Alliance and was a member of the project team for this publication.

 Topography Map (pdf)


Raritan Headwaters Geology Map

Raritan Headwaters Geology Map


The present surface features of northern New Jersey are due almost entirely to erosion of older and higher land masses and the effects of the Wisconsin glaciation that left behind the terminal moraine which constitutes a narrow band of the Highlands region. A small area of the terminal moraine intersects the very northern portion of our watershed near Budd Lake. The geologic formations of the Highlands region are estimated to be approximately 1 billion years old. Elevations in the northern part of the Basin in the Highlands average approximately 1,000 feet above msl, while the southern part of the Highlands shows valley contours reaching a low of 350 feet. Ridges of the Highlands have resisted erosion due to the very hard rock, (sandstone, gneiss, granite, marble, quartzite, igneous and metamorphic material) of which they are made. Highland valleys consist of much softer materials of limestone or shale, making them less resistant to erosion. The soils of the Highlands have been weathered from glacial till deposits and eroding bedrock and are generally shallow and stony, with frequent rock outcrops.


The bedrock of the Piedmont is comprised primarily of consolidated shales, siltstones, sandstones, conglomerates, and igneous rocks. The Piedmont is comprised of gently rolling terrain, which is dissected by a series of broad, winding river valleys. The gentle contour of the landscape is interrupted by a number of distinctly higher, rocky ridges and hills, including Cushetunk Mountain which surrounds Round Valley Reservoir, and the Sourland Mountains, which formed from the diabase or basaltic rocks which are much harder than the shale and sandstone of the Piedmont lowlands. Exposed rock and soil at the surface of the Piedmont is the product of intense weathering of local bedrock and the influence that glacial ice sheets had on the landscape. Continuous cycles of freezing and thawing in the rocks and soils produced landform characteristics consisting of subsurface depressions and uneven ground. Meltwater streams deposited sediment on the landscape and subsequent weathering and erosion have continued to shape and reshape the surface and produce the modern soil profile of the Piedmont province.

Raritan Headwaters Geology Map (pdf)


RHA Soils Map

RHA Soil Associations Map


The dominant soils within the Highlands region of our watershed consist of the Parker and Gladstone (formerly Edneyville) series. These are well-drained, gravelly sandy loams and loams formed in weathered gneissic bedrock in the uplands. Annandale soils, formed in old glacial till, are also extensive on broad undulating ridgetops. These soils are well-drained but contain a water restrictive horizon (fragipan) in the subsoil. Bartley, a moderately well-drained soil formed in old glacial till or colluvium, is important in the limestone valleys. Poorly drained Cokesbury soils, also formed in old glacial till or colluvium, are found in depressions and waterways. Some very poorly drained soils, also found in depressions or along low-gradient streams, are formed in organic deposits (Carlisle series).


The most extensive soil in the Piedmont area is the Penn series. This is a moderately deep (20 to 40 inches to bedrock), well-drained, silty soil formed in weathered red shale. Other important well-drained, deep soils formed from sedimentary rocks include Bucks (red shale), Quakertown and Hazleton (sandstone), and Pattenburg (red conglomerate). Areas of shallow soils, (less than 20 inches to bedrock), Klinesville, and poorly drained soils are also found on uplands.

Soils associated with Round Valley and the Sourland Mountains formed in weathered igneous rocks, diabase or basalt. The important series are the well-drained Neshaminy and moderately well-drained Mt. Lucas.

RHA Soil Association Map (pdf)

Vegetation and Wildlife


Vegetative communities of the ridgetops, steep slopes, and rock outcroppings of the Highlands are dominated primarily by Chestnut-Oak forests. Species occupying this forest type include chestnut oak, red oak, black birch, tulip tree, white ash, basswood, and sugar maple. Smaller trees and saplings that constitute the understory include flowering dogwood. An array of herbs, ferns, and mosses provide ground cover. Grasses, sedges, and annuals are abundant on drier slopes.

Upland vegetative communities of the Highlands consist primarily of three forest types which include the Mixed-Oak forest, the Hemlock-Mixed Hardwood forest, and the Sugar Maple-Mixed Hardwood forest. Mixed-Oak forests consist of varying mixtures of large trees including red, white and black oak; hickory; maple; ash; beech; and elm to name a few. Smaller trees, shrubs, and vines comprise much of the understory.

Slopes of the Highlands underlain by gneiss formations contain a different forest type called the Hemlock-Mixed Hardwood forest. This vegetative community occurs in cool, moist ravines like the Ken Lockwood Gorge and on steep, lower, north-facing slopes. Dominant species in the tree canopy include hemlock, oak, birch, maple, beech, and scattered individuals of several other species.

Many of the fertile limestone valleys of the Highlands have been cleared of their natural vegetation which included the Sugar Maple-Mixed Hardwood forest which consisted of various species of oak and hickory, as well as ash, birch, maple, basswood, and beech. Scattered trees of hemlock, white pine, American elm and black walnut are found in some of the remaining wooded areas of the limestone valleys.

Forests of the Highlands provide habitat for approximately 23 threatened and endangered species and 120 resident bird species. The forested ridges provide critical nesting habitat and migration corridors for migratory songbirds and other avian species. Large contiguous forests provide nesting and foraging opportunities for several species of hawks and owls (birds of prey).

Wetlands, lakes and streams of the Highlands region support endangered and threatened species including bog turtle and wood turtle as well as large populations of small mammals, butterflies, moths and dragonflies.

Other wildlife species of the Highlands include black bear, beaver, coyote, river otter, wild turkey, white-tailed deer and an occasional bobcat.


RHA Landscape v3.1 Map

RHA Landscape v3.1 Map

Mixed-Oak forests typically found in the Highlands also occur in the Piedmont, particularly on flat expanses of sandstone and shale and on the slopes of the diabase and basalt ridges of the Sourlands. Dominant trees of the Piedmont include white oak, hickory, maple, beech, ash, and cherry. Maple-leaved viburnum and black haw are the common shrubs of well-drained areas, while moist forests include an abundance of spicebush and arrowwood and a diversity of common herbs.

Lowlands of the Piedmont consist of hardwood wetlands communities and a number of species commonly found on floodplains. Meadowland communities are dominated by cattail and a number of flood tolerant shrubs, grasses, and herbs.

In our watershed, the Piedmont province is still dominated primarily by farm fields, pastures, woodlands, swamps, and rocky ridges. Fortunately, large tracts of land within this area have been preserved as public open space. Abandoned farm fields of the Piedmont consist of pioneer species or species that have occurred as a result of natural succession.

Wildlife species of the Piedmont region are typically found in forested areas and fallow fields. Uncultivated fields provide valuable habitat for many edge-dwelling species and endangered grassland birds. Field edges containing sassafras, dogwood, viburnum, gray birch, and blackberry and raspberry brambles provide shelter and foraging opportunities for an array of wildlife species including white-tailed deer and red fox. Migratory songbirds rely on the interior of Piedmont forests, and a variety of toads and turtles reside in drier soils of higher elevations. Commonly seen mammals consist of eastern chipmunk, gray squirrel, eastern cottontail, woodchuck, and white-tailed deer. Flowering plants attract an array of insects and birds and loose soils attract small mammals, which attract red fox, hawks, and owls.

Land Use

RHA Land Use Map

RHA Land Use Map

There is a great diversity of land uses within the watershed including undeveloped land, agricultural areas, and generally small population centers. Historically, development centered in small villages and towns, often following the stream corridors which served as early economic engines in the region by serving as transportation corridors and energy for mills. In more recent decades–post-1950–suburban development has been focused along major highway corridors (I-78, I-287 and I-80, Rts. 22, 10, and 46, Rts. 206, and 24 and Rt. 517). As a result, population density is highest in the northern portion of the watershed along the I-80 corridor, along the I-287 and I-78 corridors, and along state route 31 and route 206.

Over the past 20 years, development has become more diffuse and sprawling in nature. Most communities within the watershed have instituted large lot zoning regulations (ranging from 3-12 acres per dwelling unit). While this has limited density and served in some cases to maintain valued aesthetic qualities within a community, it has also resulted in a more sprawling land use pattern that has rapidly increased per-capita land use and has acted to further fragment critical wildlife habitat. This land use pattern has made development less predictable, and thus more difficult to appropriately plan for.

While widely valued within the community for providing open space, agriculture is also implicated in water quality problems, contributing sediment, phosphorous and fecal coliform to the rivers and streams. The environmental challenges posed by agricultural uses are exacerbated by the contract nature of most contemporary agriculture in the watershed. Most farms in the watershed are privately owned for residential estate purposes and leased to farmers. The lack of long-term connection to the land being farmed often results in less sustainable practices, including less productive crop rotation cycles and a greater concern with short-term productivity.