Discovering 4,500 Years of Patuxent River History with Magnetic Susceptibility, Fluxgate Gradiometry
Billingsley (18PR9) is situated on a prominent bluff overlooking the marshy confluence of Western Branch and the Patuxent River near Jug Bay. It was a favorite spot for avocational archaeologists throughout the twentieth century who walked its vast fields and picked up artifacts left by the countless Native people who lived in this area for at least 13,000 years. The 1670 Augustin Herrman map tells us that there were villages named “Wighkawamecq” and “Coppahan” on this bluff and historic documents suggest that the Native people remained until the early 1700s. But Billingsley is a huge property, encompassing over 150 acres, and there was little indication of precisely where these settlements were located.
Archaeologists with the Maryland Historical Trust (MHT) and the Maryland-National Capital Park and Planning Commission (M-NCPPC), Department of Parks and Recreation, Prince George’s County recently partnered with the Archeological Society of Maryland (ASM) to search for the remains of the late-seventeenth century villages. The team also wanted to understand more about the long period of occupation at the site, considering that the artifacts collected by avocational archaeologists at Billingsley spanned over 9,000 years of human occupation representing the Early Archaic through the Late Woodland period.
After establishing a site grid, the archaeologists conducted several remote sensing surveys with multiple techniques to glimpse beneath the surface of the Billingsley fields. The team first used a magnetic susceptibility (MagSusc) meter to determine areas of enhanced cultural activity. This tool works by inducing a magnetic field and then determining how soils react. After processing the MagSusc data, the archaeologists realized they’d found a large area of anomalous soil in the south field and brought out the fluxgate gradiometer to narrow down where to excavate (Figure 1).
Figure 1. Magnetic Susceptibility Results
Fluxgate gradiometers are powerful instruments that use magnetometers mounted in an array to detect slight differences in the Earth’s magnetic field. These magnetic anomalies might be caused by buried metallic objects, features containing soils with elevated levels of magnetic oxides resulting from high-intensity burning, like hearths or kilns, or even small post holes and palisades. The gradiometer data is processed to create a map revealing magnetic anomalies that might be cultural features.
The results of the gradiometer survey suggested that there were several magnetic anomalies worth investigating further. This information helped guide the placement of units excavated during the 2019 and 2021 Field Sessions at Billingsley (Figure 2).
Finally, metal detecting was used as a method of narrowing down where to look for Contact period Native occupations. The Maryland Free State Treasure Club worked with MHT and M-NCPPC to search for brass arrowheads, often found on sites from the time period. None were found, but brass scrap of a similar gauge ultimately pointed the team to a concentration of Late Woodland/Contact-era artifacts.
Figure 2. Fluxgate Gradiometry Results
Ground-truthing is always the final judge that determines if anomalies detected by remote sensing are cultural or natural. In this case, in every unit where the gradiometer predicted a cultural feature, one was encountered, including a buried living surface, hearths, and large pit features, all of which yielded artifacts and carbonized plant and animal remains.
Carbonized nutshells recovered from several Billingsley features were Accelerator Mass Spectrometry (AMS) radiocarbon dated. The AMS dates indicate reuse of the site for at least 4,500 years. Several Late Archaic pit features dated between 2500 and 2100 BC. One small hearth produced a Late Woodland calibrated date between AD 1400 and 1435. Another small hearth found near a concentration of Late Woodland/Contact-era artifacts yielded a date of AD 1458-1631, suggestive of a Late Woodland or Contact period component.
While the remote sensing surveys did not pinpoint the remains of the two presumably substantial Native villages of “Wighkawamecq” and “Coppahan”, they did reveal the location of a large and robust Late Archaic settlement that thrived 4,500 years ago and was used and reused for millennia, including during the Early Woodland, Middle Woodland, Late Woodland, and Contact periods. It seems clear that Billingsley, like many other sites in the surrounding Jug Bay Complex, can lend insight into thousands of years of history if archaeologists only know where to look.