I. Introduction
From Extraction to Exposure
Buck Mine is located on Pine Hill Road in Millstone Township, Monmouth County. The township is named after the Millstone River, a major tributary of the Raritan River that shaped the region’s early settlement and economy. For much of the 20th century, this quiet ridge was known primarily for its sand, which was used in everything from roadbeds to building foundations across central New Jersey. It was one of many small mines that supported postwar development, quietly supplying material for the infrastructure of a changing state.
The site is privately owned and operated by William H. Stone and Lesley (Buck) Stone. Their family name remains rooted in the land through their company, Buck Mining & Materials Inc.
On a clear afternoon, the mine lies still. A breeze moves through the pines along the ridge, carrying the scent of damp soil and weathered stone. Below, the excavation cuts deep into the hillside, with stepped terraces descending not only through soil but also through time.
Near the surface, the sand is pale and dry, soft enough to crumble under a boot heel. Beneath that, the walls turn dark, exposing dense, iron-rich beds formed from ancient seabeds. Deeper still, the colors shift again, fading into muted amber as older sands reappear. Each layer marks a distinct chapter of Earth’s history, a natural mural composed of sediment and silence.
What began as a routine mining operation has revealed one of the most geologically informative landscapes in the state. Within the exposed layers lies a detailed record of ancient environments, including shorelines, seabeds, and sediments deposited over millions of years.
Today, most of the machinery is gone and the motion has stopped. In the stillness, the land reveals its history. It records shifting climates, the rise and fall of marine life, and the long rhythms of the geologic past. Much of what is now visible has never been seen by the public. Many features still await detailed study.
Buck Mine is no longer a place where material is removed. It has become a place where knowledge is uncovered. This chronicle presents the story of how a spent sand pit became a window into deep time, and how a group of scientists, conservationists, and community leaders worked to preserve what might otherwise have been lost.
II. Historical Context
Pine Hill Before Excavation
Before this place became a pit, it was a patch of high ground in Millstone Township. Locals knew it as Pine Hill, a modest rise with a wide view over surrounding fields and creeks. It was not steep or dramatic, but it stood apart from the landscape. On clear days, it offered one of the farthest views in the area.
Historic maps confirm its presence in the local geography. The 1851 Lightfoot map of Monmouth County labels Pine Hill clearly, surrounded by scattered farms and early roads. Later surveys from the 1870s and 1880s also mark it as a familiar landmark. It helped define property boundaries, guide travelers, and serve as a geographic anchor in a region shaped by gentle topography.
For generations, the hill was part of everyday life. The soil was sandy and well drained, suitable for certain crops but prone to drying quickly. Small farms came and went. Families cleared woodlots and worked the land in seasonal cycles. There was nothing unusual about it then, just a named hill with a good view.
No Lenape names are recorded for Pine Hill, but the land was certainly known long before the earliest maps. In a landscape defined by slope and water flow, a rise like this would have been easily recognized. It sat at the headwaters of many local streams, where the terrain began to divide and drain outward in all directions.
Aerial photographs from 1930 show Pine Hill as a dense forest, untouched by industrial development. A solid canopy covers the hilltop, bordered by farm fields, orchards, and narrow roads. Property lines remain visible, many still following patterns established generations earlier. From above, the hill is both a geographic and visual anchor. There is no sign yet of the excavation that would follow in later decades.
No one could have predicted what was hidden below. For most of its history, Pine Hill was part of the background. It shaped how people moved through the land but kept its deeper story concealed.
The Mining Years and Transformation of the Ridge
In the years following World War II, central New Jersey began to change. Cities expanded outward, and quiet rural areas were drawn into the reach of new highways, housing developments, and increasing demand for raw materials. The ridge in Millstone Township, once covered in farms and pine woods, became a resource.
Mining operations began gradually. Crews stripped away the topsoil and removed the loose surface sands, loading them onto trucks bound for construction sites across the region. The hill was taken down in stages. Each season, the elevation dropped slightly, altering the shape of the land.
Over time, the excavation deepened. What began as surface-level removal became a full-scale mining operation. Machines cut long terraces into the slope, forming a wide, stepped pit. The work was steady and methodical. Material left the site by the truckload, used for roads, foundations, and backfill. A natural rise in the land was slowly transformed into an open excavation.
By the time production slowed, nearly fifty feet of elevation had been removed. What remained was no longer a hill, but a broad pit surrounded by exposed walls of sediment. Most people saw it as just another spent site, nearing the end of its usefulness. But something unexpected had been left behind. The stripped walls began to reveal a different kind of value.
III. Geological Significance & Preservation Efforts
Recognition of Geological Significance
In the summer of 2019, Joseph J. Serio, an inspector accredited by the Mine Safety and Health Administration and a geological and natural resources conservation specialist with the Ocean County Soil Conservation District, visited Buck Mine and the adjoining Campo Mine alongside Paul Califano, Assistant District Manager of the Freehold Soil Conservation District. The visit was routine. The owners were preparing closure plans that included stormwater management, vegetative stabilization, and a return to a more natural grade.
As their truck eased into the excavation pit, Serio noticed the greenish tint characteristic of Cretaceous greensands and felt a jolt of recognition. He paused to steady his breath and allowed himself a quiet grin. It was the unmistakable response of a geologist when training, experience, and anticipation converge in the field. On an otherwise ordinary day, the sedimentary record had revealed something extraordinary.
Califano was not there as a stratigrapher, but he listened. He weighed Serio’s excitement against the soil erosion and sediment control plans and quickly understood the potential value of what was exposed. If these walls truly held a clear slice of deep time, perhaps the right path was not to bury them, but to consider preservation.
They walked the pit walls slowly, scanning each face like lines in a book. The bedding was sharp and continuous, arranged in bands that caught the light differently with each step. Near the base, pale sand glimmered in muted tones of amber and gold. Higher up, the colors shifted abruptly to deep greens and browns, beds marked by glauconite and iron. To a trained eye, it was clear: this was not a random pile of disturbed sediment, but a well-preserved sequence. Layer by layer, it told the story of Earth’s transition from the age of dinosaurs to the time that followed. The close of the Cretaceous and the beginning of the Paleogene were exposed in place.
What struck Serio most was how unnoticed it all seemed. Local mining traditions had long simplified the language. The glauconitic beds were dismissed as “clay,” and all yellow sands were casually labeled “Englishtown,” a familiar trade name in pits across the region. But the stratigraphy told a more complex and precise story.
Standard reclamation would have buried these exposures under thousands of cubic yards of fill. The opportunity to study them, and to share what they revealed, would have been lost. Serio and Califano left the pit with a new sense of purpose. They had arrived to inspect a mine preparing for closure. They left ready to advocate for a rare geologic record of extinction and recovery, one that deserved to remain visible.
Building Support for Preservation
Recognition was only the beginning. Once we understood the scientific value of what the Buck Mine exposed, the next question was how to ensure it would not be buried or forgotten. The first step was simple but essential: to bring others to see it for themselves.
We reached out to John Showler, who was then the State Erosion Control Engineer. We explained that the pit walls contained one of the clearest records of geologic time remaining in New Jersey. To support the case, we prepared a brochure with photographs, stratigraphic sketches, and fossil examples from the site . With paper in hand, we began inviting others to stand with us.
An on-site walkthrough followed. John Showler, the mine owners, their engineers, county officials, and conservation staff joined us on the excavation floor. As we pointed to the exposed layers, we described what each one represented: ancient seas, the extinction horizon, and the return of life that followed. Seeing it in person conveyed a sense of significance that words alone could not.
Momentum built quickly. John Showler issued a formal letter of support. His endorsement gave the effort official recognition and marked the site as more than a local point of interest. It was now understood as a resource with statewide significance.
Original, brochure style informational pamphlet detailing the unique geological features exposed at the Buck and adjoining Campo mines as distributed to raise awareness and gain support for preservation. Prepared in September of 2019 by Joseph J. Serio, OCSCD.
We also contacted scientists who had studied New Jersey’s deep past for decades. Dr. Ken Miller of Rutgers University, known for his work on the Cretaceous to Paleogene boundary, and Dr. David Parris, longtime curator at the New Jersey State Museum, were both invited to evaluate the exposures. To support their research, Serio provided bulk sediment samples and fossil material collected from the pit. Their expertise, combined with the voices of local and state officials, began forming a coalition strong enough to challenge the default approach to reclamation.
What began with one realization in the field was now a shared effort. Buck Mine had found its advocates.
Dated October 20, 2019, this form records the delivery of three flats of fossil-bearing sediment collected by Joseph J. Serio, OCSCD, from Pine Hill Road in Millstone Township, Monmouth County, New Jersey. The specimens were received by Dr. David C. Parris at NJSM for examination and potential inclusion in the museum’s Natural History collection.
Stratigraphy and Scientific Value Inside the Pit
Buck Mine is more than an excavation. Its walls preserve a sequence of formations that span the end of the Cretaceous and the beginning of the Paleogene, one of the most dramatic transitions in Earth history, which occurred about 66 million years ago. At the base lies the Red Bank Formation, a reddish to brown quartz sand deposited during the late Cretaceous. Above it rests the glauconitic Tinton Formation, often cemented into iron-rich ledges, which represents the final Cretaceous seas of New Jersey. Overlying the Tinton is the Hornerstown Formation, a Paleocene unit whose contact with the Tinton marks the transition across the extinction boundary. In some places, the contact is sharp; in others, it appears burrowed and reworked. In every case, it represents the recovery of life after catastrophe. Higher in the sequence, thin remnants of the Vincentown Formation may be present, followed by the much younger Kirkwood and Cohansey Formations of Miocene age. These later deposits contain lighter, cross-bedded sands that record shifting river and coastal systems.
This stratigraphic stack is more than a visual record. It also preserves a chemical signature of global significance. In the 2000s, core drilling in collaboration with Rutgers University recovered continuous samples across the boundary interval at several New Jersey sites, including Buck Mine. The Buck Pit 1 core, now housed at the Rutgers Core Repository, contains a distinct iridium anomaly peaking at 0.43 parts per billion within a clay unit approximately 33 centimeters thick that overlies the Tinton Formation. Although microtektites were not reported from that core, outcrop studies in the same belt documented clay clasts with embedded spherules, as reported by Esmeray-Senlet and colleagues in 2016. These findings confirm the presence of impact-derived material and support a geochemical signal tied to the Chicxulub event. Together, the physical and chemical evidence connect New Jersey’s coastal plain to the global effects of the end-Cretaceous asteroid impact.
The pit walls also preserve fossil burrows, feeding traces, and internal molds of marine invertebrates, along with polished shear surfaces and other deformation features that record changes long after burial.
Field Observations and Fossil Documentation
On June 26, 2025, Joseph J. Serio visited Buck Mine and was joined by Marc Rogoff, a representative of the New Jersey Department of Environmental Protection. Together, they met with Lesley Buck and held discussions with local officials about planned activities and the broader potential of the site. Ideas were raised for future interpretive displays and how core samples might serve both scientific and public purposes.
In the pit, attention focused on the fossil-bearing beds. The upper Hornerstown Formation revealed burrows, feeding traces, and phosphatized internal molds or nodules. Found at the contact between the uppermost Tinton Formation and the lowermost Hornerstown Formation was an internal mold of the extinct bivalve Cucullaea, an index fossil of the Cretaceous . Specimens of this species had already been collected and formally deposited by Serio in the repositories of the New Jersey State Museum and Rutgers University. Other invertebrate material from the same horizon shows affinities with both the latest Cretaceous and earliest Paleocene faunas, further underscoring the transitional nature of the boundary. These small finds serve as direct evidence of ancient marine life and highlight the importance of systematic fossil collection for science and conservation.
The most striking features, however, were structural rather than fossiliferous. Just above the Tinton Formation, Serio identified diagenetic shear surfaces with polished textures resembling slickenlines. Hand samples previously provided to Dr. David Parris at the New Jersey State Museum had led to speculation that these features resulted from mining activity. Their occurrence in freshly exposed, undisturbed sections confirmed instead that they were natural. Additional samples were collected for further analysis, with the potential to reveal new information about post-depositional processes. Similar surfaces were observed at the ferruginous hardground that caps the Tinton, suggesting a broader pattern of deformation. Such shear features are rarely reported for this stratigraphic interval, making their presence at Buck Mine a potentially significant observation. These findings, along with the supporting samples, were reported to Dr. Ken Miller at Rutgers to inform ongoing site interpretations.
Testing of practical coring methods was also conducted using a one-inch steel soil sampler. Despite the compact nature of the Tinton layer, the tool produced nearly intact cores both vertically and horizontally. The success of this method opened new possibilities for sampling and for sharing the site’s geology with the broader public.
That day at Buck Mine combined field science with forward-looking planning. Fossils, structures, and core samples all spoke to the scientific value of the site, while cooperation among landowners, state representatives, and local officials demonstrated a growing commitment to its preservation.
Cucullaea and Boundary Complexity
The presence of Cucullaea near the contact between the Tinton and Hornerstown Formations has long been a subject of interest in New Jersey geology. In some locations, specimens appear to have been reworked from older Cretaceous deposits. In others, they occur within Paleocene sediments. The examples from Buck Mine, preserved as phosphatized internal molds, contribute directly to this ongoing discussion. Whether these specimens were reworked or deposited in place, they illustrate the complex processes of erosion, reburial, and preservation that shaped the Cretaceous to Paleogene boundary. Each specimen offers evidence that helps refine our understanding of extinction, recovery, and sedimentation along the New Jersey Coastal Plain.
Unusual Structural Features in Boundary Sediments
Published studies on the succession from the Tinton Formation to the Hornerstown Formation have focused primarily on fossils, geochemical signatures, and the placement of the boundary itself. Polished shear planes that resemble slickenlines are not widely reported from these formations. Their presence at Buck Mine, observed in undisturbed exposures, suggests a layer-parallel style of diagenetic deformation concentrated along the ferruginous hardground and within clay-rich seams.
If confirmed through microtextural analysis, these features would introduce a new line of evidence for understanding how these greensands were modified after burial. The structural observations at Buck Mine may therefore represent an underreported aspect of post-depositional history in this region.
Toward Restoration and Public Access
Buck Mine now stands at the edge of transition. With only a few final contracts remaining, the owners are preparing to move from active extraction to site restoration. This process is being carried out in coordination with state and local government agencies, with the possibility that the property may eventually become part of the Monmouth County Park System.
Restoration efforts will focus on stabilizing slopes, managing surface water, and encouraging natural re-vegetation. At the same time, plans aim to preserve the most significant geologic exposures for future study.
For now, the site remains closed to the public. This restriction protects both visitors and the fragile outcrops that make the site unique. However, important groundwork has already been laid. Discussions with county officials, scientists, and educators have begun to shape a vision for controlled access.
The long-term goal is for Buck Mine to become accessible in a way that balances education and preservation. One day, students, researchers, and residents may walk the site, view the exposed layers, and connect directly with the geologic history of the region. Access would follow clear guidelines to ensure that the site remains protected for future generations.
Preservation, Interpretation, and Responsibility
At the Ocean County Soil Conservation District office, a single core sample from Buck Mine stands upright in its display. It shows a series of layered sands and clays, each with distinct textures and colors. Within those bands lies a record that spans millions of years and holds scientific value that is still being studied. For us, the core is more than a geologic specimen. It is a symbol of what can be protected when science, community, and stewardship align.
The transformation of Buck Mine from a spent sand pit into a recognized geologic site is a shift in both perception and purpose. What was once valued only for what it provided to the construction industry is now valued for what it reveals about the past. This change did not happen on its own. It required observation, advocacy, and a willingness to preserve what would otherwise be lost.
A detailed sedimentary log of the boundary section was prepared to support outreach and education. It highlights the iron-cemented Tinton hardground, the overlying dark clay that records the Chicxulub impact and extinction event, and the basal Hornerstown beds that show the early stages of recovery. The core and associated field log make the science accessible and help ensure that the importance of the site can be understood by a wider audience.
Pictured is the OCSCD interpretive core of the K-Pg boundary at Buck Mine, Millstone, New Jersey (June 26, 2025). The log and photographs trace the 5.2′ horizontally cored section from the upper Tilton Formation.
Our task now is to make sure the story continues. The layers at Buck Mine are not renewable. Once altered or covered, their scientific value is lost. Preserving them means future generations will be able to see what we see, to study what we study, and to connect directly with this record of deep time. In doing so, they will inherit not only a preserved site, but a model of how local action can protect irreplaceable natural history.
IV. Dedication
This chronicle is dedicated to John Showler, whose insight and quiet determination helped turn the idea of preserving Buck Mine into a real possibility. As State Erosion Control Engineer, John brought technical rigor to every project. What set him apart, however, was his respect for both the science and the people involved.
When the future of Buck Mine was uncertain, John stepped forward. His letter of support did more than add credibility. It signaled that the state recognized the exposures as a resource worth protecting. That act gave our effort momentum at a moment when it might have stalled. It marked him not only as an administrator, but as a steward.
Colleagues know John as a mentor, a thoughtful problem solver, and a steady presence in challenging times. Friends appreciate his ability to listen carefully before responding with clarity and empathy. He has been both a professional ally and a personal advocate, helping to ensure that science remained visible and valued despite changes in policy and direction.Now retired, John’s influence continues through the work we carry on. His legacy lives in every preserved ridge, every slope stabilized with foresight, and every young professional who learned by his example. Buck Mine is only one part of that story, but it is a lasting one. For that, the state of New Jersey owes him not only respect, but gratitude.
V. References
Esmeray-Senlet, S., Miller, K. G., Sherrell, R. M., Senlet, T., Vellekoop, J., and Brinkhuis, H. (2016). Iridium profiles and delivery across the Cretaceous and Paleogene boundary. Earth and Planetary Science Letters, 457, 21–33
John & Maureen Buck, whose family established and operated Buck Mine for decades. The sand and gravel they supplied helped build roads, homes, and landmarks across New Jersey. That legacy is now carried forward through stewardship and conservation. Image courtesy of Buck Mining & Materials Inc.
Special thanks to Tim Thomas, FSCD District Manager and Paul Califano, FSCD Assistant District Manager, and all the other conservationists who’ve lended their support to the continued preservation of New Jersey’s geological and natural resources.
Key Takeaways: Why the Buck Mine Matters to New Jersey
- Preserves a clear record of the K–Pg boundary (~66 million years ago)
- Yields important fossils such as Cucullaea and other transitional species
- Displays unusual structural features (slickenlines) rarely reported in this interval
- Holds potential as a site for education, research, and future public access
- Represents the legacy of the Buck family, whose materials helped build roads, homes, and even landmarks like Six Flags Great Adventure.
Want to Learn More About Buck Mine?
Download a copy of Stratigraphy and Stewardship: A Chronicle of Conservation at Buck Mine of Millstone Township, New Jersey, by Joseph Serio. Ocean County Soil Conservation District is committed to protecting and preserving New Jersey’s unique geological and natural resources. Stay tuned for future updates on all of our conservation initiatives and educational opportunities.
Contact: jserio@SoilDistrict.org | Contact: education@SoilDistrict.org
Although clearly outside the political boundaries which define the jurisdictional area of Ocean County Soil Conservation District in the implementation of the Soil Erosion and Sediment Control Act of New Jersey (N.J.S.A. 4:24-39 et. seq.), the significance of the Buck Mine site transcends this limitation and the District fully supports the continue involvement of Joseph Serio, OCSCD, in assisting, in any reasonable manner, to investigate, engage and inform interested entities as requested an available. Visit the District’s website, www.soildistrict.org, to explore the important work and educational opportunities.