The Geology of Morristown National Historical Park, New Jersey

Morristown National Historical Park in New Jersey preserves the ground where the Continental Army spent two winters of the American Revolution. It also sits astride one of the region's major geologic boundaries, where rocks more than a billion years apart meet along a fault. This summary draws on the National Park Service's Geodiversity Atlas, which gathers what the NPS Geologic Resources Inventory knows about each park's rocks, sediments, landforms, fossils, soils and the processes that shape them.

The park

The park takes in the 18th-century village of Morristown in Morris County, about 48 km (30 mi) west of New York City. Authorized on March 2, 1933, it was the nation's first designated national historical park, and it covers about 692 hectares (1,711 acres).

It protects the structures, features, archeological sites and collections of the Continental Army's winter encampments of 1777–1778 and 1779–1780, General George Washington's headquarters, and related Revolutionary War sites. It has four separate units: Washington's Headquarters, Fort Nonsense, Jockey Hollow and the New Jersey Brigade area. In the winter of 1779–1780, the park notes, Washington held the army together through disease, food shortages, expiring enlistments and the worst winter of the century.

Winter at Morristown National Historical Park. Image from the National Park Service's page.

A park on a fault line

Morristown lies on the tectonic boundary between the Reading Prong and the Piedmont, two regions made of very different rocks and separated by the Ramapo Fault. The park's geology falls into three main groups:

• Mesoproterozoic metamorphic and igneous rocks. The oldest bedrock, west of the fault: granite and gneiss of the Byram Intrusive Suite and Losee Metamorphic Suite.
• Jurassic sedimentary rocks. Sandstone, siltstone and mudstone of the Boonton Formation, east of the fault, underlying the Washington's Headquarters Unit.
• Quaternary surface deposits. During the Pleistocene, repeated advances of glaciers reshaped the land and left thick layers of loose till. Streams and rivers later reworked the till into alluvial, swamp, terrace and slope deposits.

The Geodiversity Atlas places the park in the New England Highlands Physiographic Province, next to the Piedmont Physiographic Province, and notes that it shares its geologic history and characteristic formations with a region far beyond its boundaries.

Geologic Resources Inventory map. National Park Service.

Maps and inventories

The Geologic Resources Inventory produces digital geologic maps, reports and posters for more than 270 natural resource parks, and a Soil Resources Inventory has also been completed for Morristown. Both are available through the NPS DataStore.

Sources

• National Park Service, "NPS Geodiversity Atlas—Morristown National Historical Park, New Jersey": https://www.nps.gov/articles/nps-geodiversity-atlas-morristown-national-historical-park-new-jersey.htm
• The report cover shown on the source page is not reproduced.