How was the Sourland Mountain geophysical region created?
Sourland Mountain, whose highest elevation is 568 feet, is less
of a mountain and more of a hill. It is made of volcanic rock, but there
was never a volcano in this part of New Jersey. The mountain is covered
with enormous, rounded and smooth boulders that look as if they were
carried here by moving ice, but no glacier ever came within fifty miles of
During the Jurassic Age, 195-135 million years ago, lava from the mantle below the Earth’s surface forced its way upwards and slid forcefully between the existing horizontal sedimentary layers, cooking the parts it touched, and cooling very slowly because it was not exposed to the cool
air above the ground. Over millions of years as the tectonic plates
continued to slide east and west the ground, no longer flat, was forced to fold up into what is now our Sourland Ridge, running about seventeen miles from northeast to southwest. All of this pressure caused large cracks, called faults, and smaller cracks, called fractures, which to this day form the primary source of groundwater storage for the wells on Sourland Mountain. Even today, the softer layers of sedimentary rock have continued to erode, leaving the hard diabase and argillite layers which define the mountain.
All streams atop the mountain are headwaters, and feed most of the 19 streams and rivers in the Sourland region, which then flow into two main watersheds, the Delaware and Raritan Rivers.
Settlement on Sourland Mountain has always been constricted by scarcity of water. Its hard bedrock impedes penetration of water into aquifers (underground geological formations containing or conducting ground water), resulting in limited supplies of water that can be withdrawn through domestic wells, which are the primary source of potable water in the region.
However, water running off the mountain during precipitation events led to the formation of narrow "hollows", that allowed the creation of mills during the 18th century.
Land Cover/Land Use
Land cover and use in the Sourland region has been in a constant state of flux, since the first native Americans arrived thousands of years ago, who cleared the forests for villages and small agricultural plots. Forest removal on a much larger scale occurred with the arrival of the Dutch British. Throughout the 18th and 19th centuries, mountain streams were used to harness power for mills, which ground grains and other agricultural products, as well as lumber (evidence of these mills can be seen along Rock Brook, just north of the modern Zion AME Church, in Montgomery Township). During this period, pottery manufacture began (taking advantage of the valley's clay soils) and quarries were dug to extract the hard diabase rock, used for railroad ballast and road building.
By the mid-19th century, most forest cover on the mountain had been depleted. In their place, farms sprang up on the mountain, and rural villages were formed, including African American sites like Minnietown and Wycoff Corner. These people supported the peach industry that was thriving on top of the mountain. Railroads serviced the agricultural industry, and their train stations could be found in Stoutsburg, Hopewell, and Skillman.
The maps above represent land cover/land use change in the area surrounding the current site of the Mt Zion AME Church. The map on left is based on B&W aerial imagery taken in the 1930's, with wooded areas tinted in green; the map on the right is color aerial imagery taken in 2015, with the 1930's wooded areas over-layed.
Note how significantly the land use and cover have changed over the past 80+ years. Nearly all of the agricultural fields have disappeared. The amount of tree coverage in this extent has more than tripled, and suburban residential growth is scattered throughout.
Maps produced by Kevin Burkman, GIS Analyst, SSAAM, 2018
The end of the 19th century brought major changes to the land cover and land use of the Sourland region. A peach blight brought destroyed the peach orchards, sending the African Americans who serviced them into the valleys below, and beyond. Further, a regional shift in the economy slowly ended other agriculture on the mountain. Rural villages, such as Zion, Minnietown and Wycoff Corner disappeared, while forest reclaimed abandoned farmland.
Until the mid 20th century, Sourland Mountain remained a relatively remote part of New Jersey. New road construction, however, soon connected the region to nearby urban areas. With this accessibility, profound changes began to occur. Land cover and use in the Sourland region, as we know it today, began to creep across the landscape; agricultural areas in the valleys and lower slopes of the mountain gave way to suburban neighborhoods. Meanwhile atop the ridge, orchards, fields and pasture lands from the 19th century gave way first to scrub habitat, then a mature, contiguous hardwood forest. That forest today is one of the few unbroken habitats in New Jersey, and serves as a refuge for threatened birds, amphibians and plants, as well as a source of clean water for the region.
Source: Sourland Conservancy, New Jersey's Sourland Mountain (T.J. Luce)