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National Battlefield


cover of park brochure

park geology subheading
Photo of cannons at Antietam
Antietam National Battlefield, Maryland

The Valley and Ridge province has developed on thick, folded beds of sedimentary rock deposited during the Paleozoic. The differing degrees of resistance to erosion of sandstones, shales, and carbonate rocks comprising the lithology determine local relief. In general, the more resistant sandstones cap the ridgetops, protecting the softer bedrock below from erosion. Limestones and dolomites, which underlie ANTI, form the lowlands and valleys. As shown in Figure 5, four major rock units have been mapped by the Maryland Geologic Survey in ANTI; Conococheague Limestone, Elbrook Limestone, Waynesboro Formation (siltstone, shale, sandstone, dolomite), and Tomstown Dolomite. About 89 percent of the Hagerstown Valley is underlain by carbonate rocks. More than 50 known caves and about 200 wells intersecting cavernous zones attest to the development of caverns in the carbonate rocks of the valley (Duigon, 2002). The NPS is required to manage ANTI's karst terrain to maintain the inherent integrity of its water quality, spring flow, drainage patterns, and caves (National Park Service, 2001). The eastern and western boundaries of the Hagerstown Valley are major faults separating the valley from areas having greater relief and different lithology and structure (Duigon, 2001).

Military Geology

It was over this karst terrain that the two armies clashed. The Union forces taking up position on the far side of Antietam Creek to the east of the visitors center. The small stream valley created by the north-to-south flow of the creek is somewhat hidden from view. The Confederate forces concentrated their strength in a curved line of defense running along Hagerstown Pike to the southern end of Sharpsburg, terminating at the heights, composed of the Waynesboro Formation, overlooking Antietam Creek at the Burnside Bridge. Union forces were sent north to cross the creek at one of the several fords in open view of Lee's position, thus allowing him to shift his lines to the impending attack on his northern flank. Opening engagements came from the North Woods and the Cornfield. Later in the morning the battle shifted toward the center of Lee's line and concentrated around the Sunken Road (Bloody Lane). The four hours of fighting along Sunken Road resulted in 5,000 casualties. Union forces were unable to cross Burnside Bridge throughout most of the day due to a commanding position held by a small Confederate force of Georgians along the heights overlooking the bridge. By the time General Burnside's forces managed to cross, the element of surprise was lost. With the loss of surprise and the arrival of more Confederate troops along the heights, the Union forces withdrew to the other side of Antietam Creek (White, 1997). The single bloodiest battle of the American Civil War was over for the day.


ANTI is located in the Valley and Ridge physiographic province (Figure 4). The Valley and Ridge province is characterized by elongate parallel ridges and valleys that are underlain by folded sedimentary rock. The characteristic topography of this region is the result of differential weathering of linear belts of rocks. More specifically, ANTI is located in the Great Valley, a subprovince of the Valley and Ridge. The Great Valley is characterized by a karstic landscape where many cavern and sensitive aquatic habitats are located (William & Mary, 2000). Locally around ANTI, the Great Valley subprovince is referred to as the Hagerstown Valley of Washington County, Maryland (Duigon, 1997).


The unconsolidated sediments overlying the rocks in the Hagerstown Valley include transported materials as well as materials formed in place. Transported materials comprise alluvium and terrace deposits along streams, and colluvium along the flanks of mountains east and west. The materials formed in place include weathering products and soils. Total soil thickness varies from nothing (exposed bedrock) to over 100 feet in the valley (Duigon, 2001). Depending on the parent material, soils of the Hagerstown Valley tend to be medium texture, well drained, and deep to shallow. Parallel linear outcrops (clints) may separate areas of deep soil (grikes). These outcrops are the edges of steeply dipping strata, and the deep soil between them has formed along the bedding planes (Duigon, 2001). The Hagerstown Valley contains limestone-derived soils that are highly productive for agriculture uses. Many acres of forests have been cleared in the Great Valley region for agriculture. The Nature Conservancy has estimated that only 1500 acres of an original 500,000 acres of limestone forest remains undisturbed in Maryland (National Park Service, 1996). ANTI currently has the 2002 Washington County Soil Survey for the battlefield entered in the park's geographic information system (GIS). Soil resources at ANTI are to be preserved; thus, the unnatural erosion, physical removal, and contamination of soils will be prevented to the extent possible (Wenschhof, 1997). Park management is encouraged to consider crop selection, crop rotation, minimum tillage, grassed waterways, mulching, contour farming, strip farming, terracing, and the use of various soil amendments when designing a land use plan for a historic district where the interpretive theme calls for using agricultural tillage practices (National Park Service, 1991).


The battlefield is located within the 14,670 square mile Potomac River drainage basin, the fourth largest watershed on the East Coast (Belval and Sprague, 1999; National Park Service, 1995a). The Potomac River flows for 385 miles from the Allegheny Mountains to the Chesapeake Bay. Draining almost 15,000 square miles in four states, the Potomac is a major natural resource (National Park Service, 1995). The Potomac is one of nine river basins, and the second largest drainage that form the 64,000 square mile Chesapeake Bay watershed (see Figure 6). The Chesapeake Bay is the largest estuary in the United States, providing habitat for abundant and diverse wildlife populations and supporting an economy that includes fishing, shipping, and recreation. Currently, 136 million people live in the Chesapeake Bay watershed, which is challenged with unprecedented development (Burke et al., 1999). Within the Potomac River drainage basin, ANTI is located within the Conococheague- Opequon watershed [USGS cataloging unit: 02070004] (Figure 7a). More specifically, the battlefield is contained within the Antietam Creek drainage of this watershed, draining 281 square miles at ANTI before emptying into the Potomac River (Figure 7b). A detailed map of the Antietam Creek drainage basin is included in a recent report (Duigon, 2001) prepared by the Maryland Geologic Survey. Sixty percent of the Antietam Creek drainage basin is within Washington County, Maryland (U.S. Army Crops of Engineers, 1972). Land use within this basin is 69 percent agriculture, 24 percent forest and 7 percent urban (U.S. Geological Survey, 1995).

Ground Water Wells and Springs

There are a number of ground water wells and springs at the battlefield. Wells that are no longer in use should be considered for plugging and abandonment since they provide a pathway for contaminants to enter the shallow karst aquifers at ANTI. Some of these inactive wells may have value for future ground water monitoring or research projects, if so, they should be properly protected from surface influences. Chemical applications to crops and animal wastes from grazing livestock (cattle) at the battlefield are concerns for both wells and springs. To protect wells and springs, the park should delineate ground water flow regimes and sensitive recharge areas (e.g., exposed limestone, sinkholes, etc.) at ANTI, and work to eliminate the application of chemicals and direct livestock access to these locations. A field survey identified two possible sinkholes on the Poffenberger Farm, located at the West Woods reforestation area north of Confederate Avenue. Both areas were observed to be full of trash, suggesting these areas being used as dumps by local landowners (Wenschhof, 1997). Unfortunately, this practice is common in karst landscapes, where sinkholes appear to be an appropriate place to dispose of trash. Nothing could be further from the truth, since these areas represent important recharge locations for ANTI's aquifers. Delineation of the recharge areas and ground water flows for karst aquifers underlying the battlefield is very important. In some cases, the ground water flow system boundaries may coincide with surface drainage basin boundaries, but in karst terrain, they commonly do not (Duigon, 2001). It has been suggested by the Maryland Department of Natural Resources (1997) that true watershed delineation by dye tracing methods is not practical at ANTI due to the small size of aquifers and high associated costs. The author disagrees with this conclusion. Delineation of a catchment basin in karst geology is typically approached through dye tracing techniques due to the unpredictable nature of carbonate hydrogeology. If there are several small aquifers in the area, this increases the complexity of ground water flow, and validates the need for dye tracing, in concert with other tools (e.g., potentiometric surface maps, ground water chemistry, etc), to confirm flow paths. Failure to understand ground water flows at ANTI can be costly, not only from a natural resources perspective, but also from a cultural resources perspective. For example, the NPS drilled a geothermal well, adjacent to the Mumma springhouse, as part of the climate control system for the newly restored Mumma Farmhouse. Drilling this well altered the Mumma Spring flow, resulting in a new flow path. Now, ground water enters the historic springhouse at a reduced flow rate. The primary flow path appears to travel beneath the foundation of the springhouse before entering back into the historic surface drainage. Significant undercutting was observed around the springhouse foundation as a result of this new subsurface flow. After realizing the drilling impacts to the spring, the geothermal well was closed. Geothermal wells were then installed several hundred feet away from the spring to meet the needs of the climate control system.

Source National Park Service, Water Resources Division

Cover of Antietam report

Geologic Resource Evaluation Report – A detailed geologic report is available that provides an introduction to the geologic history of the park and its geologic formations, identifies geologic features and processes that are important to park ecosystems, describes key resource management challenges and possible solutions, and lists geologic research and monitoring needs.


Duigon, M.T. 1997. A brief discussion of the Project, "Karst Hydrogeology in the Hagerstown Valley, Maryland and its Influence on Ground-Water-Quality Protection". Maryland Geologic Survey. Baltimore , MD. 2 pp.

Duigon, M.T. 2001. Karst Hydrogeology of the Hagerstown Valley , Maryland . Report of Investigations No. 73. Maryland Geologic Survey. Baltimore , MD. 128 pp.

Duigon, M.T. 2002. Karst Hydrogeology of the Hagerstown Valley, Maryland (abstract). Maryland Geologic Survey. Baltimore , MD. 1 p.

Maryland Department of Natural Resources. 1999. 1999 Maryland 's Rural Legacy Awards. http://www.dnr.state.md.us/rurallegacy/rlnews/99awards.html

National Park Service, 1995. Baseline Water Quality Data, Inventory and Analysis, Antietam National Battlefield. Water Resources Division and Servicewide Inventory and Monitoring Program. Ft. Collins, CO. 308 pp. + appendices.

National Park Service. 2001. National Park Service, Management Policies. Washington D.C. Ch. 4.

U.S. Army Corps of Engineers, 1972. Antietam Creek Floodplain Information. Washington County , Maryland . Baltimore District.

U.S. Geological Survey, 1995. Selected herbicides in major streams in the Potomac River basin upstream from Washington , D.C. NAWQA Fact Sheet 107-95. Townson , MD. 4 pp.

Wenschhof, E.R., Jr. 1997. Identification of Sensitive Soil and Water Resources and Evaluation of Agricultural Conservation Practices at Antietam National Battlefield, Sharpsburg , Maryland (unpubl. Master thesis). Shippensburg University . Shippensburg , Pennsylvania . 97 pp. + appendices.

White, W.R. 1997. Military Geology: Antietam Battlefield. http://www.howard.kl2. md.us/white/AntietamFT.html.

William & Mary. 2000. The Geology of Virginia . The College of William and Mary, Williamsburg , Virginia . URL:http//www.wm.edu/cas/geology/ virginial coastal_plain.html, piedmont.html, blue_ridge.html, valley_ridge.html, coastal_plain.html

park maps subheading

The General park map handed out at the visitor center is available on the park's map webpage.

For information about topographic maps, geologic maps, and geologic data sets, please see the geologic maps page.

photo album subheading

A geology photo album for this park can be found here.

For information on other photo collections featuring National Park geology, please see the Image Sources page.

books, videos, cds subheading

Currently, we do not have a listing for a park-specific geoscinece book. The park's geology may be described in regional or state geology texts.

Please visit the Geology Books and Media webpage for additional sources such as text books, theme books, CD ROMs, and technical reports.

Parks and Plates: The Geology of Our National Parks, Monuments & Seashores.
Lillie, Robert J., 2005.
W.W. Norton and Company.
ISBN 0-393-92407-6
9" x 10.75", paperback, 550 pages, full color throughout

The spectacular geology in our national parks provides the answers to many questions about the Earth. The answers can be appreciated through plate tectonics, an exciting way to understand the ongoing natural processes that sculpt our landscape. Parks and Plates is a visual and scientific voyage of discovery!

Ordering from your National Park Cooperative Associations' bookstores helps to support programs in the parks. Please visit the bookstore locator for park books and much more.

geologic research subheading


For information about permits that are required for conducting geologic research activities in National Parks, see the Permits Information page.

The NPS maintains a searchable data base of research needs that have been identified by parks.

A bibliography of geologic references is being prepared for each park through the Geologic Resources Evaluation Program (GRE). Please see the GRE website for more information and contacts.

selected links subheading

NPS Geology and Soils Partners

NRCS logoAssociation of American State Geologists
NRCS logoGeological Society of America
NRCS logoNatural Resource Conservation Service - Soils
USGS logo U.S. Geological Survey

teacher feature subheading

Currently, we do not have a listing for any park-specific geology education programs or activities.

General information about the park's education and intrepretive programs is available on the park's education webpage.

For resources and information on teaching geology using National Park examples, see the Students & Teachers pages.
updated on 01/04/2005  I   http://www.nature.nps.gov/geology/parks/anti/index.cfm   I  Email: Webmaster
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