Geology of Antietam National Battlefield, Maryland

Geodiversity is the full range of a park's geologic resources — rocks, minerals, sediments, fossils, landforms and the processes that shape them — together with its soils. The National Park Service's Geodiversity Atlas, produced by the Geologic Resources Inventory, collects that information for education, geoconservation and the joint management of each park's living and non-living resources.

The park

• Antietam National Battlefield lies just outside Sharpsburg, Maryland, about 14 km (9 miles) north of Harpers Ferry in Washington County.
• Established on August 30, 1890, it covers about 1,307 hectares (3,230 acres).
• It commemorates the bloodiest single-day battle in American history. The 1862 Battle of Antietam ended Robert E. Lee's first invasion of the North and left more than 23,000 soldiers killed, wounded or missing.
• Photographs taken in the days after the battle were among the first to show the public the horrors of the Civil War.
• The battle gave President Lincoln the opening to issue the preliminary Emancipation Proclamation.
• One of the best-preserved Civil War sites in the park system, it includes the battlefield, monuments, roads, fences, an observation tower and tablets marking troop movements and artillery, many placed by the War Department.

Geologic setting

Antietam sits in the Great Valley section (the Shenandoah Valley in Virginia) of the Valley and Ridge province — long, parallel ridges separated by valleys, often with karst topography over carbonate rock. Its rolling hills, farms, fields and pastures still recall the battle era.

• The bedrock is carbonate and clastic sedimentary rock laid down in the Cambrian and Ordovician on the margin of Laurentia, ancestral North America.
• Buried for about 200 million years, the rocks were then folded and uplifted in the late Paleozoic Alleghenian Orogeny, about 285 million years ago.
• Most of the park rests on the Cambrian Elbrook Limestone and the Cambrian–Ordovician Conococheague Limestone, including its Big Spring Station Member.
• Sinkholes occur across most of the area's carbonate formations, especially the Elbrook and Conococheague.
• The eastern part of the park lies on older Cambrian units: the Waynesboro Formation (Red Run, Cavetown and Chewsville members) and the Tomstown Formation (Dargan Member).

Protected resources

• Fossils in national parks are protected by the Paleontological Resources Preservation Act of 2009.
• Caves are protected by the Federal Cave Resources Protection Act of 1988.
• Abandoned mineral lands can be valuable cultural sites and habitat but can also endanger visitors and wildlife and harm water, landscapes and resources — stay out and stay alive.

A small flag in front of the headstones around the colossal Private Soldier Monument at Antietam National Cemetery. NPS photo.

Maps and reports

The Geologic Resources Inventory produces digital geologic maps and reports for more than 270 natural resource parks — scoping summaries, GIS maps, reports, posters and project overviews. A Soil Resources Inventory has also been completed for Antietam. All are available through the NPS DataStore.

Sources

Based on "NPS Geodiversity Atlas—Antietam National Battlefield, Maryland," National Park Service; a work of the United States government in the public domain.