Intro 

As one of the original outlets for Glacial Lake Passaic, Moggy Hollow Natural Area offers a view into the prehistoric landscape that once was present in Northern New Jersey. Located in Far Hills, Somerset County, the park was added to the National Registry of Natural Landmarks (1) in 1970 (2; 3). Known for its marshy wetlands and steep ravines, Moggy Hollow holds tremendous natural beauty and gives space for local biodiversity to thrive (4). 

Historical development

During the formation of Glacial Lake Passaic, the ancient Wisconsinan Glacier that covered Northern New Jersey began to melt and recede (4). As the glacier melted, water began to collect in an oval basin located between the Watchung Mountains to the east and the Highlands ridges in the west (5). This basin would eventually become the bottom floor for Lake Passaic, which reached its maximum size about 11,000 years ago (5). 

At its largest size, Glacial Lake Passaic was estimated to be 30 miles long ranging from Wayne to Bedminster, about 10 miles wide, and an average depth of 160 – 200 feet deep (1; 6). As broken fragments of ice and debris melted from the glacier, they naturally blocked gaps within the mountain ranges, allowing the basin to continue to fill (5). Sediments from the melting glacier covered the bottom of the lake, forming depths estimated to be over 300 feet (5). These layers of sediment are still present in the form of wetlands and marsh habitats scattered throughout the former lake’s location. 

Eventually the basin found an outlet to release its waters through Moggy Hollow. This location was the primary delta for Glacial Lake Passaic for over 2,000 years (7). The remnants of this ancient delta are still visible in the drastic 90-foot gorge within Moggy Hollow, as well as the wetland habitat that surrounds the protected natural area (7; 2). The waters that drained out of Moggy Hollow carved a gravity-fed route through natural terrain, eventually connecting to a branch of the Raritan river (8). The constant flow of rushing water crafted unique structures in the rock formations at Moggy Hollow, and continue to shape the landscape to this day (9). 

After enough glacial water had retreated out of Lake Passaic, the levels of the lake lowered and created new outlets for water to escape. A gap near present-day Paterson became exposed, known as the Paterson Great Falls, and the ancient lake began to permanently drain (9). Smaller, postglacial lakes began to form as the massive Lake Passaic was dwindling in size, and eventually disappeared entirely. However, natural landscapes in this region still show signs of the lasting effect this ancient lake had. There are abundant ecosystems composed of marshes, floodplains and swamps found in this area, along with the soil composition having hundreds of feet or silt or clay that was deposited from glacial movement and melting (8). 

Local Species 

Moggy Hollow does not only have historical significance, but its natural habitat plays a pivotal role in the survival and growth of many local species. Flora and fauna utilize this protected space to reproduce, forage and seek protection from the suburban landscape that surrounds them. There are hundreds of plant species that grow within the Passaic Basin region, with 10 state-listed species and even a federally listed species being present called Swamp Pink (Helonias bullata) (5). Many migratory birds use Moggy Hollow as a stopover habitat in their long migration routes, and raptors are frequently spotted hunting within the basin (5). There is a large presence of wetland vegetation, due to the historical composition of the region. Various species of cattails (Typha spp.) and sedges (Carex spp.) make up marshes and shrub swamps, with the majority of forested swamps being red maple (Acer rubrum) (5). With many native mammals, amphibians and reptiles from along the Eastern United States, this region has important breeding areas for the endangered Indiana Bat (Myotis sodalis) and the threatened Box Turtle (Clemmys muhlenbergii). It is also worth noting that the Passaic Basin has the only identified population of the blue-spotted salamander (Ambystoma laterale) (5). 

However, Moggy Hollow and the Passaic Basin face prominent challenges in terms of its conservation efforts, with pollution, overdevelopment and habitat fragmentation being the highest risks for the area’s protection (5). Many conservation efforts have been established within the Passaic River Watershed, such as riparian forest buffers for erosion control and eliminating sources of pollution throughout the region (10). Floodplain management is a prominent conservation initiative that protects the natural floodplains from development and improves its natural ways of mitigating water absorption for the habitat (4). Restoration projects have also been a main focus, with the planting of native species and efforts to restore ecosystems back to their original, balanced state (4). There has also been a huge focus on land acquisition, with over 20,000 acres being collected to provide protection for the Basin (4).

The location of Moggy Hollow holds tremendous historical and natural significance, with its prehistoric characteristics still prevalent in our modern world. Due to these qualities, the park was selected for inclusion in the National Registry of Natural Landmarks – a program run by the National Park Service – in 1970 (7). Being a NNL site, the park is not only able to stay protected, but is naturally conserved to encourage greater appreciation for the region’s rich history and future growth (11). The Moggy Hollow Natural Area is an environment with close to no human influence, and is a pristine example of how important environmental preservation is for plants, animals and people combined. 

About the Author

Stella Mueller is a recent college graduate from the University of Rhode Island. She earned a M.S. in Environmental Communication in 2025, along with a B.A. in Journalism and a B.S. in Wildlife & Conservation Biology in 2024. During graduate school, Stella joined the DWELL Lab as a Communication Assistant, working in collaboration with the National Park Service to create updated multimedia products for NPS locations. She worked primarily with National Natural Landmark (NNL) sites in Northern New Jersey, where she designed updated posters, brochures and augmented reality (AR) experiences for park visitor engagement. Stella is currently pursuing a career in science communication and education, looking to share her appreciation for the natural world with future audiences.

Works cited: 

1. “Moggy Hollow | Somerset County Park Commission, NJ.” Somersetcountyparks.org, 2025, www.somersetcountyparks.org/leonard-j-buck-garden/pages/moggy-hollow. 
2.  “National Natural Landmarks – National Natural Landmarks (U.S. National Park Service).” Nps.gov, 2025, www.nps.gov/subjects/nnlandmarks/site.htm?Site=MOHO-NJ. 
3. Staff, Editorial. “Moggy Hollow.” The Official Site for the Historical Society of the Somerset Hills (THSSH), 26 Feb. 2024, somersethillshistoricalsociety.org/2024/02/26/moggy-hollow
4. Jones, Madison. “Central Passaic Basin (NNL /NPS/ESA).” Uri.edu, 2025, web.uri.edu/dwell/nnl-nps/.
5. U.S. Fish and Wildlife Service . “New Jersey’s Central Passaic Basin.” Fws.gov, Feb. 2007, www.fws.gov/sites/default/files/documents/Cent_Passaic_basin_508.pdf.
6. Jones, Madison . “Remediation Page.” Google.com, 2024, www.google.com/maps/ 
7. “Moggy Hollow Natural Area – Raritan Headwaters.” Raritan Headwaters, 24 Sept. 2018, www.raritanheadwaters.org/preserves-map-page/moggy-hollow-natural-area/ 
8. NJ Geological Survey, NJ Department of Environmental Protection. Unearthing New Jersey. 2007, www.nj.gov/dep/njgs/enviroed/newsletter/v3n2.pdf 
9. Edelson, Alan . “Moggy Hollow Historical Marker.” Hmdb.org, 16 June 2016, www.hmdb.org/m.asp?m=18700. 
10. Passaic River Coalition. “Passaic River Watershed Issues.” Passaic River Coalition (PRC), passaicriver.org/passaic-river-basin/watershed-issues/.
11. “National Natural Landmarks (U.S. National Park Service).” Www.nps.gov, www.nps.gov/subjects/nnlandmarks/index.htm.