National Park Service U.S. Department of the Interior

Natural Resource Program Center

Prince William Forest Park Geologic Resources Inventory Report

Natural Resource Report NPS/NRPC/GRD/NRR—2009/086 THIS PAGE: South Fork Quantico Creek

ON THE COVER: Bridge over South Fork Quantico Creek

NPS Photos Prince William Forest Park Geologic Resources Inventory Report

Natural Resource Report NPS/NRPC/GRD/NRR—2009/086

Geologic Resources Division Natural Resource Program Center P.O. Box 25287 Denver, Colorado 80225

March 2009

U.S. Department of the Interior National Park Service Natural Resource Program Center Denver, Colorado The Natural Resource Publication series addresses natural resource topics that are of interest and applicability to a broad readership in the National Park Service and to others in the management of natural resources, including the scientific community, the public, and the NPS conservation and environmental constituencies. Manuscripts are peer-reviewed to ensure that the information is scientifically credible, technically accurate, appropriately written for the intended audience, and is designed and published in a professional manner.

Natural Resource Reports are the designated medium for disseminating high priority, current natural resource management information with managerial application. The series targets a general, diverse audience, and may contain NPS policy considerations or address sensitive issues of management applicability. Examples of the diverse array of reports published in this series include vital signs monitoring plans; "how to" resource management papers; proceedings of resource management workshops or conferences; annual reports of resource programs or divisions of the Natural Resource Program Center; resource action plans; fact sheets; and regularly-published newsletters.

Views, statements, findings, conclusions, recommendations and data in this report are solely those of the author(s) and do not necessarily reflect views and policies of the U.S. Department of the Interior, National Park Service. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the National Park Service.

Printed copies of reports in these series may be produced in a limited quantity and they are only available as long as the supply lasts. This report is also available online from the Geologic Resources Inventory website (http://www.nature.nps.gov/geology/inventory/ gre_publications.cfm) and the Natural Resource Publication Management website (http:// www.nature.nps.gov/publications/NRPM/index.cfm) or by sending a request to the address on the back cover. Please cite this publication as:

Thornberry-Ehrlich, T. 2009. Prince William Forest Park Geologic Resources Inventory Report. Natural Resource Report NPS/NRPC/GRD/NRR—2009/086. National Park Service, Denver, Colorado.

ii NPS D-54, March 2009

Contents

Figures ...... iv

Executive Summary ...... 1

Introduction ...... 2 Purpose of the Geologic Resources Inventory ...... 2 History of Prince William Forest Park ...... 2 Geologic Setting ...... 2

Geologic Issues ...... 6 Mining-Related Issues ...... 6 Geology and Biodiversity ...... 6 Recreational Demands ...... 7 Water Issues ...... 7 Erosion and Slope Processes...... 8 Paleontology ...... 8 Geologic Education and Research ...... 9

Geologic Features and Processes ...... 14 Geology and the Landscape ...... 14 Regional Structure ...... 14 Quantico Falls ...... 15

Map Unit Properties ...... 19 Map Unit Properties Table ...... 21

Geologic History...... 23

Glossary ...... 30

References ...... 34

Appendix A: Geologic Map Graphic...... 36

Appendix B: Scoping Summary ...... 39

Attachment 1: Geologic Resources Inventory CD

PRWI Geologic Resources Inventory Report iii Figures Figure 1.Map of Prince William Forest Park ...... 4 Figure 2. Physiographic Province Map of Virginia...... 5 Figure 3. Erosion from foot traffic along South Valley Trail ...... 10 Figure 4. A buttress along South Fork Quantico Creek...... 11 Figure 5. Top-down view of a gabion along shoreline of South Fork Quantico Creek ...... 12 Figure 6. Undercut slope along banks of South Fork Quantico Creek ...... 12 Figure 7. Gullying along South Valley Trail...... 13 Figure 8. Diagram showing effects of slope processes and erosion along Quantico Creek ...... 13 Figure 9. Map of Prince William County ...... 16 Figure 10. Generalized cross section through Prince William County ...... 17 Figure 11. Quantico Falls ...... 17 Figure 12. Steeply dipping gneissic beds underlying Quantico Falls...... 18 Figure 13: Geologic time scale ...... 26 Figures 14-16. Geologic evolution of the Appalachian Mountains in the Prince William Forest Park area ...... 27-29

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Executive Summary

This report accompanies the digital geologic map for Prince William Forest Park in Virginia, which the Geologic Resources Division produced in collaboration with its partners. It contains information relevant to resource management and scientific research. This document incorporates preexisting geologic information and does not include new data or additional fieldwork.

Prince William Forest Park begins with the geology, that further impacts of visitors are only just beginning to be is, with the processes that formed the present-day measured and alleviated. Researchers are striving to environments and scenery. Understanding the geologic better understand all these impacts on the environment. resources is relevant to resource-management decisions about geologic issues, future scientific research, The following issues, features, and processes were interpretive needs, and economic resources. identified as having the most geologic importance and the highest level of management significance to the park: Geologic processes formed a landscape composed of rock formations, ridge tops and valleys, waterfalls and • Mining-related issues. wetlands. These processes develop a landscape that Prince William Forest Park has a long history of influences human use patterns. The geology attracted mineral extraction—principally pyrite from the Cabin settlers to eastern Virginia to pursue hunting, mining, Branch Mine. The abandoned shafts from gold settlement, industry, and agriculture. The geology operations at the Greenwood Mine were a safety inspires wonder in visitors, and emphasis on geologic hazard. Wastes from such mines may also degrade the resources can enhance the visitor’s experience. environment by polluting water and soil through the weathering of mine tailings and other debris. The rocks in east-central Virginia reflect the tectonic forces that formed the Appalachian Mountains. Late • Geology and biodiversity. Precambrian to early Paleozoic crystalline rocks, and The park is famous for its forest biodiversity, including younger sandstone, shale, siltstone, carbonate rocks, and the largest parcel of piedmont forest in Virginia. This quartzite underlie the landscape. The region was diversity is a direct result of area geology, topography, compressed during three separate tectonic events, the and climate. Protecting ecosystems found in wetlands, Taconic, Acadian, and Alleghanian orogenies (mountain hill slopes, and ridge tops, as well as understanding the building events). The faulted and folded metamorphic relationships between geology and biology throughout gneiss underlying Prince William Forest Park records the park, remains a key resource management issue. this regional deformation. • Erosion and slope processes. The relatively wet climate of the eastern United States, Quantico Creek wanders through the largest piedmont combined with severe storms, loose soils on steep forest ecosystem in the eastern United States. Nearly the slopes, and marshy wetlands along the streams in entire Quantico Creek watershed is within the Prince William Forest Park, creates a setting that is boundaries of Prince William Forest Park. This park is especially susceptible to slumping, slope creep, and the third largest National Park Service unit in Virginia erosion of stream banks. This is commonly due to a and a natural haven in the Washington, D.C., local lack of stabilizing plant growth in the sandy, metropolitan area, some of the principal geologic issues relatively infertile and easily disturbed soils. and concerns pertain to protecting this environment. Substantial seasonal runoff and relatively frequent, Humans have significantly modified the landscape intense rainstorms also contribute to high rates of surrounding Prince William Forest Park, and erosion. Runoff can dramatically alter the landscape, consequently modified its geologic system. This system is creating new hazardous areas in the process. The dynamic and capable of noticeable change within a runoff may also clog streams with excess sediment, human life span. Geologic processes also continue to affecting hydrologic systems and aquatic life. change the landscape, making resource management a challenge. Other geologic issues concerning ground water and

surface water, recreational demands, and general In addition to natural causes of landscape change, dams, geology, were also identified as management issues for mines, roads, air and water pollution, and invasion by Prince William Forest Park. non-native species have had a significant impact on the natural resources of Prince William Forest Park. The

PRWI Geologic Resources Inventory Report 1

Introduction

The following section briefly describes the National Park Service Geologic Resources Inventory and the regional geologic setting of Prince William Forest Park.

Purpose of the Geologic Resources Inventory The park’s 18,939 acres cover a major part of the forested The Geologic Resources Inventory (GRI) is one of 12 Quantico Creek watershed (fig. 1). The park is one of the inventories funded under the National Park Service largest parcels of pristine piedmont forest land left in the (NPS) Natural Resource Challenge designed to enhance area and is the third largest National Park Service unit baseline information available to park managers. The solely in Virginia. program carries out the geologic component of the inventory effort. The Geologic Resources Division of the Prince William Forest Park is located in Prince William Natural Resource Program Center administers this County, Virginia. The land was originally set aside in the program. The GRI team relies heavily on partnerships 1930s by President Franklin D. Roosevelt’s with the U.S. Geological Survey, Colorado State administration in order to preserve a piedmont forest University, state surveys, and others in developing GRI landscape for the education and enjoyment of future products. generations. The park was formally established on June 22, 1948, by an act of Congress. The uses of the park have The goal of the GRI is to increase understanding of the varied from an outdoor education center to an Office of geologic processes at work in parks and provide sound Strategic Services training camp. The boundaries of the geologic information for use in park decision making. park have changed several times since its beginning as it Sound park stewardship relies on understanding natural has expanted to cover almost the entire Quantico Creek resources and their role in the ecosystem. Geology is the watershed. The park attracted 351,058 visitors in 2008. foundation of park ecosystems. The compilation and use of natural resource information by park managers is Geologic Setting called for in section 204 of the National Parks Omnibus The park is located within two physiographic provinces Management Act of 1998 and in NPS-75, Natural (fig. 2). The western two-thirds of the park are in the Resources Inventory and Monitoring Guideline. Piedmont province while the eastern third is located in the Atlantic Coastal Plain province. Marked differences To realize this goal, the GRI team is systematically in terrain combined with location in the transition zone conducting a scoping meeting for each of the identified between a northern and southern climate lead to 270 natural area parks and providing a park-specific ecosystem variations throughout the park and that digital geologic map and geologic report. These products supports a diversity of species. support the stewardship of park resources and are designed for nongeoscientists. Scoping meetings bring The topography within the park consists of rolling hills together park staff and geologic experts to review and narrow ridge tops separated by steep-sloped valleys available geologic maps and discuss specific geologic and ravines. The ridge tops are composed of resistant issues, features, and processes. late Precambrian to early Paleozoic metamorphic rocks. Separating the ridge tops are valleys where less resistant The GRI mapping team converts the geologic maps material, such as unconsolidated deposits, was easily identified for park use at the scoping meeting into digital eroded. Relief in the park is fairly high: elevations range geologic data in accordance with their innovative from lows of ≈3 m (≈10 ft) to heights of nearly 122 m Geographic Information Systems (GIS) Data Model. (400 ft) above sea level. These digital data sets bring an exciting interactive dimension to traditional paper maps by providing The following is a general description of the various geologic data for use in park GIS and facilitating the physiographic provinces of Virginia, including a regional incorporation of geologic considerations into a wide province, the Culpeper Basin, located just to the west of range of resource management applications. The newest Prince William Forest Park (fig. 2). maps come complete with interactive help files. This geologic report aids in the use of the map and provides Atlantic Coastal Plain Province park managers with an overview of park geology and The Atlantic Coastal Plain province is primarily flat geologic resource management issues. terrain with elevations ranging from sea level to about

≈ For additional information regarding the content of this 100 m ( 300 ft) in northern Virginia . The province was report and current GRI contact information please refer formed by sediments that were eroded from the to the Geologic Resources Inventory Web site Appalachian Highland areas to the west. These (http://www.nature.nps.gov/geology/inventory/). sediments were intermittently deposited over the past 100 million years in a wedge-shaped sequence during periods of higher sea level. These deposits were then History of Prince William Forest Park reworked by fluctuating sea levels and the continual Prince William Forest Park provides a respite in the erosive action of waves along the coastline. rapidly growing Washington, D.C., metropolitan area.

2 NPS Geologic Resources Division

The Atlantic Coastal Plain province extends north-south The boundary between the Culpeper Basin and the from New York to Florida and from the Fall Line east to Piedmont Plateau is defined by a depositional contact the Chesapeake Bay and Atlantic Ocean. Coastal Plain that is best indicated by a topographic change from the surface soils are commonly sandy or sandy loams that are rolling hills of the Piedmont to relatively flat ground in well drained. Large streams and rivers in the province, the basin. The western boundary of the basin, west of including the James, York, Rappahannock, and Potomac which lies the Blue Ridge province, is defined sharply by Rivers, are often influenced by tidal fluctuations. a system of faults, locally culminating in the large Bull Run fault (Zen and Walker 2000). Piedmont Province The “Fall Line,” or “Fall Zone,” marks a transitional zone Blue Ridge Province where the softer, less consolidated sedimentary rocks of The Blue Ridge Province extends from Georgia to the Atlantic Coastal Plain to the east intersect the harder, Pennsylvania along the eastern edge of the Appalachian more resistant metamorphic rocks to the west, forming Mountains. It contains the highest elevations in the an area of ridges and waterfalls and rapids. This zone Appalachian Mountain system, in Great Smoky covers more than 27 km (17 mi) of the Potomac River Mountains National Park in North Carolina and from Little Falls Dam, near Washington, D.C., west to Tennessee. Precambrian and Paleozoic igneous and Seneca, Maryland. Examples of this transition can be metamorphic rocks were uplifted during several seen in the Potomac Gorge of the Chesapeake and Ohio orogenic events that formed the steep, rugged terrain. Canal National Historic Park or, on a smaller scale, at Erosion resistant Cambrian quartzite forms Blue Ridge, Quantico Falls in Prince William Forest Park. Bull Run Mountain, South Mountain, and Hogback Encompassing the Fall Line, westward to the Blue Ridge Ridge in Virginia, whereas Precambrian metamorphic Mountains, is the Piedmont physiographic province. rocks underlie the valleys (Nickelsen 1956).

The eastward-sloping Piedmont Plateau was formed Eroding streams have narrowed the northern section of through a combination of folding, faulting, uplift, and the Blue Ridge Mountains into a thin band of steep erosion. These processes resulted in an eastern landscape ridges, climbing to heights of approximately 1,200 m of gently rolling hills starting at 60 m (200 ft) in elevation (3,900 ft). The Blue Ridge province is typified by steep that become gradually steeper towards the western edge terrain covered by thin, shallow soils, resulting in rapid of the province at 300 m (1,000 ft) above sea level. Soils in runoff and low ground-water recharge rates. Many of the the Piedmont Plateau are highly weathered and generally streams and rivers dominating the landscape around well drained. Prince William Forest Park begin along the slopes of the Blue Ridge, dissecting them into ridges and ravines. Culpeper Basin The Culpeper Basin is one of a series of basins that fringe Valley and Ridge Province the boundary between the Piedmont and Blue Ridge The landscape of the Valley and Ridge physiographic along the length of the Appalachian Mountains. The province is characterized by long, parallel ridges basin formed during the Mesozoic as an intermountain separated by valleys. These valleys formed where basin during an extensional tectonic event. It trends resistant sandstone ridges border more easily eroded northeast-southwest and is about 120 km (75 mi) long shale and carbonate formations. Areas dominated by and 30 km (20 mi) wide. The rocks in the basin are carbonate formations exhibit karst topography. “Karst” largely flat-lying sedimentary sandstone, siltstone, and is a term used to describe landscapes dotted by shale and include some igneous diabase and basalt. sinkholes, caves, and caverns.

The eastern part of the Valley and Ridge province is part of the Great Valley (Shenandoah Valley). It is connected to the Piedmont province by streams that cut through the Blue Ridge Mountains.

PRWI Geologic Resources Inventory Report 3

Figure 2: Location of Prince William Forest Park relative to the physiographic provinces of Virginia. Modified by Trista L. Thornberry- Ehrlich (Colorado State University) from Bailey (1999).

PRWI Geologic Resources Inventory Report 5

Geologic Issues

The National Park Service held a Geologic Resources Inventory scoping session for Prince William Forest Park on April 30−May 2, 2001, to discuss geologic resources, address the status of geologic mapping, and assess resource management issues and needs. This section synthesizes the scoping results, in particular those issues that may require attention from resource managers.

Mining-Related Issues Subsurface hazards are numerous on public lands in the Inventory, Monitoring, and Research Suggestions for United States. Many of these are sites of historic mining Mining-Related Issues activity, which pose threats due to subsidence, • Accurately map mine features within the park. contamination, and possible collapse. These threats • Use ground-penetrating radar, common offset seismic- make it difficult to maintain roads and trails through the reflection profiling, and magnetic-gradient surveying mined areas. Failures of former mines can be to identify any subsurface workings. catastrophic, and collapse would present a hazard to anyone visiting or working in the area including hikers, • Assess the risk of shaft failure in mapped mine bicyclists, horseback riders, and recreational vehicle workings. users. • Assess environmental impact of abandoned pyrite mines on ground-water quality, the hydrogeologic Abandoned pyrite and gold mines are present at Prince system, and the biologic system within the park. William Forest Park. Speculation regarding the location • and structural integrity of the main shafts of the Periodically sample and test water (surface and ground abandoned mines necessitated electrical and magnetic water) and soil to detect heavy metals, especially in geophysical surveys to locate the shafts and to assess drinking water. shaft conditions. This was a project of the U.S. Bureau of • Contact the Abandoned Mineral Lands (AML) staff at Mines (Hauser and Jessop 1995). The volcanic-hosted the Geologic Resources Division office, Denver, CO, Cabin Branch Mine is probably the most visited mine for resource management questions. feature in the park. It was extracting a Cu-Zn-Pb massive sulfide deposit from 1889 to 1919. Mining at Cabin Geology and Biodiversity Branch ceased around 1920 and left several open shafts, Natural areas provide refuges for many species. They historic remnants and foundations, and pyritic acid also serve as migration corridors for wildlife. For the tailings that resulted in some acid drainage into Quantico public, they are living classrooms. Small national parks, Creek (Seal et al. 1999b). There is also an abandoned such as Prince William Forest Park, add considerably to gold mine (Greenwood Mine) in the northwest part of the biological diversity of an entire region, especially in the park, where there are partially collapsed mine shafts areas of heavy development, such as the Washington, at Independence Hill. D.C., metropolitan area. The park is the largest protected

green space in the area. It is also one of the largest Mines and abandoned mines create a strain on the protected Piedmont forest ecosystems in the National ecosystem. At Prince William Forest Park, this strain is Park Service. manifested as low biodiversity downstream from the

Cabin Branch Pyrite Mine. In 1995, steps were taken to Prince William Forest Park provides a critical natural reclaim the site. This reclamation included the area in a dissected landscape. An understanding of the construction of storm-water diversion trenches around features that promote biodiversity, such as the geology, the tailings, grading the tailings away from the shorelines, climate, topography, and hydrogeologic system, is the addition of topsoil and pulverized limestone (to important to understanding the distribution of unique reduce acidity), and revegetation of the surface. habitats and ecosystems, as well as managing them Although the chemistry of shallow ground water still effectively for preservation and restoration. remains affected—lower pH and higher concentrations of dissolved copper are found on the northeastern bank At least two distinct types of forest ecosystems are of the creek and higher concentrations of dissolved iron present in the upland areas of the park. These areas are and sulfate are found on the southwestern side of the controlled by the underlying geology. The ridges and creek—stream waters are relatively neutral, having a pH slopes support a mixed oak forest, whereas the lower − of 6.4 7.1. Concentrations of dissolved sulfate, copper, slopes support a mesic hardwood forest above the and zinc in the stream are still higher downstream of the floodplain of the local waterways. Beeches, which are site (Seal et al. 1999a). Despite the disturbance, indicative of an undisturbed interior environment, are organisms that once fled the toxic metals and low pH present in the park, as are a variety of rare species, (acidic) waters and soils are returning to the area. including the butternut, bigtooth aspen, black walnut, swamp white oak, and cottonwood. The floodplain

6 NPS Geologic Resources Division environments in the park support American beech, box These environments can be especially fragile, and off- elder, and sycamore trees. trail hiking leads to their degradation (fig. 3). The park designates trails and picnic areas to limit the negative The park is in a transition zone between northern and impacts of recreation. Prohibited use in non-designated southern climates and between different physiographic areas increases the area of impact and places delicate provinces. This is reflected in the distribution of several ecosystems at risk for contamination by waste. species of trees in the park. For more information on the rare ecosystems in the park (a seepage swamp, remote Several streams, including Quantico Creek, enhance the stands of eastern hemlock, and populations of rare natural beauty of the park. As with hiking, overuse of plants, including the small whorled pogonia orchid certain areas can lead to contamination by waste and Isotria medeoloides), see the park’s Web site degradation of the ecosystem and also increased stream- (www.nps.gov/prwi). bank erosion. The park has attempted to buttress certain reaches of the creek where it approaches a visitor trail. Prince William Forest Park is also host to rare and These supports are intended to reduce stream bank diverse fauna. More than 38 species of mammals, 24 erosion, but such measures are temporary (figs. 4 and 5). species of amphibians, more than 100 species of birds, 27 species of reptiles, 23 species of fish, and many Inventory, Monitoring, and Research Suggestions for invertebrates share the landscape and waterways of the Recreational Demands park. Of these inventoried species, there are a few rare or • Identify and mitigate areas of trail erosion, social trails, threatened species listed by the State of Virginia, as well and human impacts on park watersheds and wetlands. as species of special concern. • Design informative exhibits to encourage responsible The geological features of the Culpeper Basin and the use of park resources. Piedmont province are major determining factors of the biodiversity of the flora and fauna protected within the Water Issues park. The ecosystem can be dramatically different In the humid eastern climate of Virginia, water seems depending on the orientation of a particular, elevation, present everywhere—in streams, rivers, runoff, springs, geologic substrate, soil type, and permeability, change in and wells. Annual precipitation at Prince William Forest slope, and exposure to climate and wind. Therefore, Park averages ≈100 cm (40 in) per year with most of the correlation with geological features and resources should rain coming during short storms in the summer months. be part of any biological inventory and monitoring effort. Because of the existing and future development of the surrounding populated areas, water resources are under Inventory, Monitoring, and Research Suggestions for constant threat of contamination and overuse. Geology and Biodiversity • Determine and study geologic controls on habitat and Preserving the integrity of the Quantico Creek watershed species distribution. is a major management objective at Prince William Forest Park, which contains approximately 70% of the entire • Create habitat maps and models that include geology watershed. The north branch of Quantico Creek and and topography in a GIS to improve understanding of South Fork Quantico Creek join near the eastern ecosystem processes and geographic distribution. boundary of the park. These streams receive more than • Monitor changes in geologic controls on species 90% of the runoff from park lands. The park also distribution, including hydrologic systems, slopes, and contains several vernal pools that serve as vital breeding human development. areas for many species. These pools are underlain by relatively impermeable geologic substrate, trapping Recreational Demands seasonal precipitation. The National Park Service has a dual mission, to protect park resources and to provide opportunities for visitors The natural course of Quantico Creek has been altered in to enjoy those resources. Prince William Forest Park the park to create recreational lakes. A series of small provides visitors numerous recreational opportunities, dams trap sediments from storm-water runoff, and these including hiking, fishing, bicycling, picnicking, dams are periodically dredged. These constructed photography, and almost any activity that does not features provide additional breeding habitat for several damage the resources of the park or endanger other fish and amphibian species. Normally, restoration of an visitors. original natural watershed would be a primary goal of the park. In this case, such a goal is tempered by the The park receives many visitors, especially during the possibility of habitat degradation for the organisms living summer months. As many as 351,058 people entered the below the dams, as well as the increase in sediment load park in 2008, placing increasing demands on the and the likelihood of intense flooding that would resources of the park. Management concerns vary from compromise park resources. Visitor expectations and trail erosion, waste treatment, and water quality to access are also determining factors in remediation historic mine shaft stability. proposals.

Many trails wind through preserved biological, Although its course has been altered, the creek is a historical, and geological environments at the park. “reference stream” regarded by various federal, state,

PRWI Geologic Resources Inventory Report 7 and local entities as an example of a pristine, unspoiled of slopes by roads, trails, and other development in watershed. Even so, issues related to the health of the addition to natural erosion and weathering. streams and lakes in the park still exist. Suburban development surrounding Prince William Forest Park, The walls of many of the river and tributary valleys part of the Washington, D.C., metropolitan area, affects within and around the park are steep and high (fig. 6). the watershed in a variety of ways. They are dangerous because of the likelihood of rock falls, landslides, slumps, and slope creep. This is a major Where agricultural remnants, construction materials, concern in the areas of weaker rock units, such as and other wastes are present, nitrogen levels (and other fractured siltstone and unconsolidated alluvium. Slopes contaminants) in the water may reach dangerous levels. composed of unconsolidated deposits are especially Runoff from roadways commonly contains high levels of vulnerable to failure. Heavy rainstorms, common in the oil and other car emissions, which are carried into park eastern United States, can quickly saturate valley slopes. waterways and seep into the soil. Knowledge of the On slopes that lack stabilizing vegetation, rock and soil chemicals used in regional agriculture and development may mobilize and slide downhill as a massive slump or projects, and an understanding of the hydrogeologic debris flow. Slides along streams and rivers lead to system, including ground-water flow patterns, are shoreline erosion, increased sediment load, and gullying, essential to protect the watershed’s ecosystem. all of which threaten trails, bridges, and other features of interest in addition to visitor safety (figs. 7 and 8). The movement of nutrients and contaminants through Sediment load and distribution affect the location and the ecosystem can be modeled by monitoring the health of aquatic and riparian ecosystems. Increased composition of system inputs, such as rainfall, and sediment load can cause turbidity which adversely affects outputs, such as streamflow. Other input sources include aquatic plants and animals. Sediment loading can also wind, surface runoff, ground water, sewage, landfills, and result in changes to channel morphology and overbank fill dirt. Streams in effect integrate the surface runoff and flooding frequency affecting the riparian zones on either ground-water flow of their watersheds. Thus, they side of the stream. If the sediments entrain harmful provide a cumulative measure of the status of the substances, these can be deposited in overbank deposits, watershed’s hydrologic system. Consistent measurement poisoning the plants within the riparian zone. of these parameters is necessary to establish baselines for comparison. Inventory, Monitoring, and Research Suggestions for Erosion and Slope Processes The hydrogeologic system changes in response to • Develop a landslide hazard model to identify increased surface runoff as well. This increase results vulnerable locations in the park using topographic, from addition of impervious surfaces, such as parking geologic, and rainfall data. lots, roads, and buildings. Sedimentation also increases • due to clearing land for development. Water temperature Monitor erosion rates at key sites. Traditional profile increases because of the insulating nature of impervious measurements (repeated seasonally and, if possible, surfaces. For example, runoff from a parking lot on a hot shortly after major storms) and repeat photography July day is much warmer than runoff from a grassy slope. may be useful tools. • Inventory areas that are susceptible to runoff flooding Inventory, Monitoring, and Research Suggestions for Water (paleoflood hydrology). Issues • Assess trails for stability and determine which trails are • Establish working relationships with the U.S. most at risk and in need of further stabilization. Geological Survey and the Virginia Geological Survey, • as well as local to national conservation groups, to Study the morphology of stream channels with respect study and monitor the park’s watershed and the to intense seasonal runoff and monitor changes in hydrology of the area for applications in channel morphology. Consult professional hydrogeology, slope creep, stream-bank erosion, and geomorphologists regarding erosional processes. other geologic hazards. • Review changes in streamflow as they indicate basin • Measure and document changes in the hydrologic dynamics, climate, and land use. regime in impacted areas of the park, such as • Assess conditions such as channel morphology, roadways, abandoned mines, trails, and visitor and seasonal flooding, and proximity to park facilities to administrative facilities. identify actual and potential “problem reaches” for • Survey species of fish and benthic organisms in the prioritized monitoring. watershed. Relate species distribution to geologic • Measure sediment load on Quantico Creek to establish controls, such as ripples, waterfalls, and vernal pools. baseline conditions for future comparative assessment. • Map and quantify subterranean recharge zones. Data will provide information relevant to decisions regarding removal or maintenance of existing dams. Erosion and Slope Processes Paleontology The topographic differences within and surrounding the park are large in some places, especially along the banks No formal paleontological inventories have been of Quantico Creek and its tributaries. The likelihood of undertaken for Prince William Forest Park, and landsliding increases with precipitation and undercutting paleontological scoping sessions have not been

8 NPS Geologic Resources Division completed for the park. However, the park has Most of the petrified wood was discovered as a result of approximately 15 specimens of petrified wood construction activities. All of the petrified wood samples accessioned into museum collections. One specimen is have been classified as Taxodium distichum or bald on display at the visitor center (Kenworthy and Santucci cypress. This taxonomy has been updated and the 2004). Fossils are non-renewable resources that require material is most likely from the Cupressaceae family, in park protection and provide opportunities for visitor the fossil wood genus Cupressoxylon, closely related to education about geology and past environments. modern sequoia and bald cypress. Cupressoxylon is the Fortunately, fossil theft does not appear to be a problem most common Early Cretaceous-aged fossil wood in the for the park at this time. area. The largest pieces of petrified wood—2m (6 ft) in length—in addition to the piece already on display in the The majority of rocks within Prince William Forest Park visitor center, have excellent interpretive potential due to are igneous or metamorphic. Fossils are not typically their size and “recognizeablility” (Kenworthy and found in igneous or metamorphic rocks, and as such Santucci 2004). fossils are not known from those units. However, the Ordovician Quantico Formation and the Potomac Group Additional fossils from the Potomac Group are likely of Early Cretaceous age are located immediately adjacent within the park. However, future discovery of fossils may to or within the park and are known to contain fossils. be difficult. The heavily forested nature of the park precludes extensive rock exposures, therefore only The Quantico Formation, previously known as Quantico stream valleys and construction projects are likely to Slate, is a dark gray-black slate (lightly metamorphosed provide exposures of the Potomac Group. Nevertheless shale) originally named for exposures along Quantico awareness of the potential paleontological resource by Creek. Limited exposures of the Quantico Formation resource managers may help to preserve any fossils have been mapped within the southeastern corner of the unearthed during future excavation activities. park, near Quantico Creek and immediately adjacent to the park boundary. Numerous fossils of a well-preserved Geologic Education and Research pelecypod bivalve, Pterinea, and poorly preserved Along with a detailed geologic map and a road or trail brachiopod specimens, tentatively identified as log, a guidebook linking Prince William Forest Park to Pholidops or Leptobolus were initially described in 1911 the other parks in the Central Appalachian region would from a locality northeast of the park along Powell Creek enhance visitor appreciation of the geologic history and (Kenworthy and Santucci 2004). dynamic processes that created the natural landscape of the park. Strategically placed wayside exhibits can also The Potomac Group is a well known, frequently help explain the geology to the visitor. fossiliferous group of formations found throughout Virginia, Maryland, and Washington, D.C. The Potomac Inventory, Monitoring, and Research Suggestions for Group has variable lithologies including light-gray to General Geology pink-gray medium to very coarse grained quartz sand, a • green clay-sand, and a dark yellow-brown sandy soft Promote geologic mapping within Prince William clay. Found within these sands and clays are abundant, County, Virginia. but generally poorly preserved, leaf and stem • Collaborate with other agencies, such as the U.S. impressions of ferns, cycads, and gymnosperms along Geological Survey and the Virginia Geological Survey, with rare silicified, or petrified, tree trunks. Upchurch et to complete and integrate geologic studies of the rivers al. (1994) report on a different floral assemblage from draining the Piedmont and Atlantic Coastal Plain. Potomac Group sediments found in a gravel pit along • Map the geology within the park to determine the Engineers Road, parallel to Chopawamsic Creek south of exact nature of the boundary between the Atlantic the U.S. Marine Corps Air Station. This assemblage Coastal Plain and the Piedmont province. contains 22 different species, including one species each of horsetail and cycadophyte, eight species of conifers • Develop interpretive exhibits discussing the geologic and 12 species of angiosperms (Upchurch et al. 1994; features (sedimentary deposits, igneous rocks, Kenworthy and Santucci 2004). deformational structures, metamorphism) underlying the park, their origins, and their significance for the The only paleontological resources cataloged within geomorphology of the area, especially with regards to Prince William Forest Park collections include various the regional mining interest. Include exhibits about the pieces and chips of petrified wood collected from tectonic history of the eastern United States. Potomac Group sediments. One shoe-box sized specimen is currently on display within the visitor center.

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Figure 3. Erosion from foot traffic along the South Valley Trail. This stairway was intended to reduce erosion of the steep slope but its purpose has been undermined by off-trail hiking. Photograph by Trista L. Thornberry-Ehrlich (Colorado State University).

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South Valley Trail

Figure 4. A buttress along South Fork Quantico Creek is intended to prevent erosion of the South Valley Trail (foreground); however, slope creep from the undercut slope above has pushed the buttress out of alignment and is compromising visitor safety along trail. Photograph by Trista L. Thornberry-Ehrlich (Colorado State University).

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Direction of slope creep

Figure 5. Top-down view of a gabion along the shoreline of South Fork Quantico Creek. This image shows the toe of the slope pushing the gabion into the stream and undermining the trail along the top of the gabion. Photograph by Trista L. Thornberry-Ehrlich (Colorado State University).

Slumping

Undercut slope

Figure 6. Undercut slope along the banks of South Fork Quantico Creek. Note the significant slumping on the steep slope of a minor tributary. Photograph by Trista L. Thornberry-Ehrlich (Colorado State University).

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South Valley Trail

Gully

Figure 7. Gullying along the South Valley Trail. Photograph by Trista L. Thornberry-Ehrlich (Colorado State University).

Figure 8. Diagram showing the effects of slope processes and erosion along Quantico Creek. Note typical deposits associated with slope processes and location of a visitor trail with respect to waterway, slopes, and hazards. Diagram not to scale and represents only those features present at Prince William Forest Park. Diagram by Trista L. Thornberry-Ehrlich (Colorado State University).

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Geologic Features and Processes

This section describes the most prominent and distinctive geologic features and processes in Prince William Forest Park.

Geology and the Landscape managers to facilitate effective resource management, as Prince William Forest Park is on the fall line between the well as baseline information on soil resources for the Piedmont and the Atlantic Coastal Plain physiographic Vital Signs Monitoring Program. Soil resource provinces (figs. 9 and 10). The Piedmont is characterized inventories equip parks with maps showing the locations by deformed metamorphic rocks (granitic and and extent of soils; data about the physical, chemical, and hornblende gneiss and mica schist) of late Precambrian biological properties of those soils; as well as information to early Paleozoic age that were thrust upon the eastern regarding potential uses and limitations of each kind of margin of North America during the mountain building soil type. The products also can be used for park events (orogenies) that formed the Appalachian interpretive programs and to identify emerging Soil Mountains. The Coastal Plain is composed of mostly Program needs. The Soils map and data products for unconsolidated sediments shed from the highlands to Prince William Forest Park are available through the the west and deposited in thick layers. These layers NPS Data Store (http://science.nature.nps.gov/nrdata/). include sand, silt, and clay, as well as gravel. Geologic Basis of Ecosystem Diversity In the two-thirds of the park that is within the Piedmont, Climate and geology at Prince William Forest Park create the topography is characterized by narrow ridges capped a setting that favors biodiversity. This region in Virginia by resistant rocks and separated by steep-sided valleys is composed of mixed deciduous/coniferous forests and ravines eroded through less resistant rocks. Some thriving in the temperate climate and relatively acidic ridges and hilltops are covered with a mantle of coastal soils. Many of the forest varieties require seasonally plain or other alluvial sediments. Relief throughout the flooded sloughs, upland basins, and back swamps, such park is fairly high. The elevation ranges from about 3 m as those on the northern branch of Quantico Creek and (10 ft) above sea level to nearly 122 m (400 ft). South Fork Quantico Creek floodplains. Others require well-drained soils, such as those with a higher rock and Intense erosion is common throughout the park and in sand content present on the higher slopes in the park, places has exposed outcrops of folded and faulted and moderate to high acidity. Upland areas underlain by bedrock. Where these beds are nearly vertical, steep hardpan clay support specific forests. Pines dominate the ridges have been carved creating ripples, rapids, and falls steepest slopes along ravines and bluffs that have along Quantico Creek. Some of these rocks represent the relatively infertile soils. Successional species such as Red fall line, or the boundary between the Coastal Plain and Cedar are found in clay-rich soils that contain few the Piedmont. This line separates relatively hard, nutrients. Relatively flat topography and poorly drained resistant rocks to the west from soft, easily eroded rocks nature of some of the soils in the park support unique to the east. In many river valleys along the eastern coast, oak species that are far less common in other areas of the this line is manifested as rapids and waterfalls. To the Piedmont. north, in the Potomac River, the fall line is as wide as 27 km (17 mi) and presented serious obstacles to upstream Primarily metamorphic rocks, such as gneiss and schist, transportation before the railroads were built (Harris et underlie the park. Unconsolidated sediments and sandy al. 1997). soils overlie the metamorphic substrate. This geology in part determines the soil types and their distribution and Substrate Types and Distribution thus influences forest types in the park. Thus, an The substrates at Prince William Forest Park are understanding of the small-scale geologic differences at generally sandy, poor in nutrients, and easily disturbed. Prince William Forest Park and their interplay with the The area sustained early tobacco farming that depleted climate, topography, and soil types is important to the ground of nutrients. Poor farming practices may also managing both the recreational landscape and the have contributed to long-term depletion of nutrients. vegetation that defines much of the natural setting. These soils have yet to recover. Their exposure on steep slopes makes them highly susceptible to erosion and to Regional Structure slumping and sliding. The types of rocks underlying the The post-Early Cretaceous Stafford fault system crosses park play a role in determining the types and distribution the area (Seiders and Mixon 1981). This system consists of soils. Geologic processes also influence characteristics of a series of northeast-trending, high-angle reverse such as pH, permeability, and thickness. faults in the unconsolidated deposits. The system is more than 68 km (42 mi) long and contains the Dumfries, Fall The Soil Resources Inventory (SRI) Program of the NPS Hill, Hazel Run, and Brooke faults. The individual Geologic Resources Division worked with the Natural segments are 16−40 km (10−25 mi) long. Separating the Resources Conservation Service (NRCS) to complete a segments are 2−4 km (1.2−2.5 mi)-wide en echelon, left- soil survey for Prince William Forest Park in 2005. The SRI Program provides user-friendly products to park

14 NPS Geologic Resources Division stepping faults that suggest dextral (right) shear on the This series of belts is interpreted to be part of an island- fault system (Dominion Nuclear North Anna 2004). arc complex accreted onto North America during the Taconic orogeny (Dominion Nuclear North Anna 2004). These faults were active from the Cretaceous to earliest After accretion and subsequent erosion of the belt rocks, Quaternary time and indicate tectonic activity along the sediments such as those that became the Quantico eastern margin of North America, long considered to be Formation were deposited in successor basins and a passive margin. Maximum vertical displacements along depositional troughs, such as the Quantico synclinorium. the faults are estimated at 30−60 m (100−200 ft). These faults commonly act as conduits to ground-water flow The Quantico synclinorium is a northeast-southwest- but can also offset and thereby seal pre-existing fractures trending structure that was compressed during the and aquifers (Nelms and Brockman 1997). Ordovician Period. Within the synclinorium, the Quantico Formation is at garnet-staurolite metamorphic In addition to these features, there are many large- to grade. The high temperatures and pressures indicated by small-scale regional faults, including the Spotsylvania, this metamorphic grade indicate pervasive tectonic Chopawamsic, and Long Branch thrusts, the Hylas shear activity in the area (Dominion Nuclear North Anna zone, the Mountain Run fault zone, and the Sturgeon 2004). Creek fault (Dominion Nuclear North Anna 2004). These and other small faults are northeast-striking, east- Quantico Falls dipping Paleozoic structures that have been reactivated Several outcrops of folded and faulted metamorphic intermittently during tectonic events since their rocks are scattered throughout the park. These rocks dip formation. nearly vertically in some areas. Where present along streambeds, these rocks form natural rapids. Many of the In particular, the Mountain Run fault zone, which runs faulted rocks occur along the fall line: the geologic along the eastern margin of the Culpeper basin to the boundary between the harder, more resistant rocks of northwest of Prince William Forest Park, was reactivated the Piedmont and the softer, unconsolidated deposits of during Mesozoic extension and again as recently as the the Atlantic Coastal Plain physiographic province. Quaternary. The fault was initially accommodating thrust movement, followed by reactivation as strike-slip Quantico Falls, along the northern branch of Quantico (dextral) and dip-slip (normal) movement. Creek, is a classic example of a fall-line feature (fig. 11). The falls cascade over nearly vertical beds of resistant The Chopawamsic and Spotsylvania thrusts bound the gneissic rock (fig. 12). More easily eroded rocks Chopawamsic belt on the west and east, respectively. downstream of the falls allow the lower reaches of the This belt of rocks extends southwestward from stream to cut more deeply, increasing the overhang of Washington, D.C., through to North Carolina. Together the ledge. with the Charlotte and Milton belts, the Chopawamsic belt makes up a broad part of the central Piedmont from Virginia to Georgia.

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Figure 9. Map of Prince William County showing location of Prince William Forest Park in relation to the Culpeper Basin and the three physiographic provinces (Blue Ridge, Piedmont, and Atlantic Coastal Plain) in the county, the fall line between the Piedmont and Coastal Plain, and other regional features. Locations are approximate. Heavy red line indicates cross section of fig. 8, below. Diagram by Trista L. Thornberry-Ehrlich (Colorado State University).

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Figure 10. Generalized cross section through Prince William County showing location of Prince William Forest Park in relation to underlying structures. Drawing not to scale; vertical dimension is exaggerated. Diagram by Trista L. Thornberry-Ehrlich (Colorado State University).

Figure 11. Quantico Falls. Resistant gneissic rocks underlie this scenic setting. Less resistant rocks below are preferentially eroded away, increasing the overhang of the ledge. Photograph by Trista L. Thornberry-Ehrlich (Colorado State University).

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Figure 12. Steeply dipping gneissic beds underlying Quantico Falls. The parallelogram represents a nearly vertical plane intersecting the rock along the yellow arrow (foliation trend). This resistant rock causes the rapids and falls along Quantico Creek. Photograph by Trista L. Thornberry-Ehrlich (Colorado State University).

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Map Unit Properties

This section identifies characteristics of map units that appear on the Geologic Resources Inventory digital geologic map of Prince William Forest Park. The accompanying table is highly generalized and for background purposes only. Ground-disturbing activities should not be permitted or denied on the basis of information in this table.

The map units in the Prince William Forest Park area can Geologic maps facilitate an understanding of Earth, its be divided into two groups on the basis of their age and processes, and the geologic history responsible for its the physiographic province where they occur. Piedmont formation. Hence, the geologic map for Prince William rocks, including those of the Chopawamsic belt, are Forest Park informed the “Geologic History,” “Geologic located on the western edges of the area. Cenozoic rocks, Features and Processes,” and “Geologic Issues” sections including unconsolidated marine sand, silt, and clay, are of this report. Geologic maps are essentially two- part of the Atlantic Coastal Plain to the east. Younger, dimensional representations of complex three- Quaternary unconsolidated deposits, such as artificial dimensional relationships. The various colors on fill, alluvium, colluvium, and terrace deposits, line river geologic maps illustrate the distribution of rocks and and stream beds and underlie developed areas. unconsolidated deposits. Bold lines that cross or separate the color patterns mark structures such as faults and The Piedmont rocks include deformed metasedimentary folds. Point symbols indicate features such as dipping and metavolcanic rocks of late Precambrian and early strata, sample localities, mines, wells, and cave openings. Paleozoic age, such as the Cambrian Lunga Reservoir, Purcell Branch, Sykesville, and Chopawamsic Incorporation of geologic data into a Geographic formations, as well as the Ordovician Quantico Information System (GIS) increases the usefulness of (“Quantico slate”) and Popes Head formations. The geologic maps by revealing the spatial relationships to predominate rock types are metadiamictite, phyllite, other natural resources and anthropogenic features. amphibolite gneiss, metasiltstone, and slate (Nelms and Geologic maps are indicators of water resources because Brockman 1997). they show which rock units are potential aquifers and are useful for finding seeps and springs. Geologic maps do Some map units, such as the Wissahikon Formation, not show soil types and are not soil maps, but they do were formed as part of the ocean floor and were then show parent material, a key factor in soil formation. smeared along the eastern edge of the continent during Furthermore, resource managers have used geologic orogenic events (Pavlides et al. 1980). These were in turn maps to make connections between geology and biology; intruded by premetamorphic granitic plutons of for instance, geologic maps have served as tools for Cambrian and/or Ordovician age, such as the Dale City, locating sensitive, threatened, and endangered plant Goldvein, and Lake Jackson plutons, and the Occoquan species, which may prefer a particular rock unit. Granite (Nelms and Brockman 1997). These crystalline rocks underlie the unconsolidated sediments of Early Although geologic maps do not show where earthquakes Cretaceous age (Potomac Group), gravel deposits, and will occur, the presence of a fault indicates past several sets of river terraces (Pavlides et al. 1980; Seiders movement and possible future seismic activity. Geologic and Mixon 1981). maps do not show where the next landslide, rockfall, or volcanic eruption will occur, but mapped deposits show Other unconsolidated map units overlying the crystalline areas that have been susceptible to such geologic rocks include the Paleocene Aquia Formation, the hazards. Geologic maps do not show archaeological or Pleistocene Tabb Formation, and Holocene alluvium and cultural resources, but past peoples may have inhabited colluvium. Sediment types range from sand, silt, gravel, or been influenced by various geomorphic features that clay, and lignite, to soil and chemically weathered are shown on geologic maps. For example, alluvial bedrock called saprolite (Nelms and Brockman 1997). terraces may preserve artifacts, and formerly inhabited Saprolite is an earthy material in which the major rock- alcoves may occur at the contact between two rock units. forming minerals (except for quartz) have been altered to clays. The material retains many textural and structural The geologic units listed in the following table characteristics of the original rock but has relatively little correspond to the accompanying digital geologic data. structural integrity (Dominion Nuclear North Anna Map units are listed in the table from youngest to oldest. 2004). Please refer to the geologic timescale (fig. 13) for the age associated with each time period. This table highlights While the pre-Holocene deposits were collected in characteristics of map units such as susceptibility to fluvial, estuarine, and marine settings, the recent hazards; the occurrence of fossils, cultural resources, sediments are fluvial deposits, marsh deposits, and soils mineral resources, and caves; and the suitability as (Nelms and Brockman 1997). These recent deposits habitat or for recreational use. drape hill slopes and fill valleys and other small depressions.

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The GRI digital geologic maps reproduce essential architecture, feature attribution, and data relationships elements of the source maps including the unit within ESRI ArcGIS software, increasing the overall descriptions, legend, map notes, graphics, and report. quality and utility of the data. GRI digital geologic map The following reference is source data for the GRI digital products include data in ESRI personal geodatabase and geologic map for Prince William Forest Park: shapefile GIS formats, layer files with feature symbology, Federal Geographic Data Committee (FGDC)-compliant Southworth, S., and D. Denenny. 2006. Geologic map of metadata, a Windows help file that contains all of the the national parks in the National Capital Region, ancillary map information and graphics, and an ESRI Washington D.C., Virginia, Maryland and West ArcMap map document file that easily displays the map Virginia. Scale 1:24,000. Open-File Report OF 2005- and connects the help file directly to the map document. 1331. Reston, VA: U.S. Geological Survey. GRI digital geologic data are included on the attached The GRI team implements a geology-GIS data model CD and are available through the NPS Data Store that standardizes map deliverables. This data model (http://science.nature.nps.gov/nrdata/) dictates GIS data structure including data layer

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Geologic History

This section describes the rocks and unconsolidated deposits that appear on the digital geologic map of William Forest Park, the environment in which those units were deposited, and the timing of geologic events that created the present landscape.

Prince William Forest Park is on the boundary between Somewhat later, 540, 470, and 360 million years ago, the Atlantic Coastal Plain and the Piedmont amphibolite, granodiorite and pegmatite, and physiographic provinces. It therefore has features of lamprophyre, respectively, intruded the sedimentary both provinces and reflects the long geologic history of rocks. Several episodes of mountain building and the Appalachian Mountains and the evolution of the continental collision that resulted in the Appalachian eastern coast of North America. The regional perspective Mountains contributed to the heat and pressure that presented here connects the landscape and geology of deformed and metamorphosed the entire sequence of the park with its surroundings. sediments, intrusive rocks, and basalt into schist, gneiss, marble, slate, and migmatite (Southworth, Fingeret, et al. The recorded history of the Appalachian Mountains 2000). begins in the Proterozoic (figs. 13 and 14A). In the mid- Proterozoic, during the Grenville orogeny, a From Early Cambrian through Early Ordovician time supercontinent formed that consisted of most of the orogenic activity along the eastern margin of the continental crust in existence at that time, including the continent began again. Known as the Taconic orogeny, crust of North America and Africa. Sedimentation, this activity involved the closing of the ocean, subduction deformation, plutonism (the intrusion of igneous rocks), of oceanic crust, formation of volcanic arcs, and uplift of and volcanism are manifested in the metamorphic gneiss continental crust (fig. 15B). In response to the overriding in the core of the modern Blue Ridge Mountains of plate thrusting westward onto the continental margin of Prince William Forest Park (Harris et al. 1997). These North America, the crust bowed downwards to create a rocks formed over a period of 100 million years and are deep basin that filled with mud and sand eroded from the more than a billion years old, making them among the highlands to the east (Harris et al. 1997). This so-called oldest rocks known in this region. They form a basement Appalachian basin was centered on what is now West upon which all other rocks of the Appalachians were Virginia (fig. 15C). These infilling sediments covered the deposited (Southworth et al. 2001). grand carbonate platform and are today represented by the shale of the Ordovician (450 million years old) The late Proterozoic (fig. 14B), roughly 600 million years Martinsburg Formation (Southworth et al. 2001). ago, brought extensional rifting to the area. The supercontinent broke up, and a sea basin formed that During the Late Ordovician, the oceanic sediments of the eventually became the Iapetus Ocean. This basin shrinking Iapetus Ocean were thrust westward onto collected many of the sediments that would eventually other deep-water sediments of the western Piedmont form the Appalachian Mountains. Some of the sediments along the Pleasant Grove fault. Sand, mud, silt, and were deposited as large submarine landslides and carbonate sediments were then deposited in the shallow turbidity flows, which today preserve their depositional marine to deltaic environment of the Appalachian basin. features. These early sediments are exposed on Catoctin The rocks that formed—sandstone, shale, siltstone, and Mountain, Short Hill−South Mountain, and Blue limestone, all now metamorphosed—currently underlie Ridge−Elk Ridge, all west of Prince William Forest Park. the Valley and Ridge province far to the west of Prince Also, in this extensional environment, flood basalt and William Forest Park (Fisher 1976). other igneous rocks, such as diabase and rhyolite, were added to the North American continent. These igneous The Piedmont metasediments, which cover rocks were intruded through cracks in the granitic gneiss approximately two-thirds of Prince William Forest Park, of the Blue Ridge core and extruded onto the land record the transition from non-orogenic, passive-margin surface during the break-up of the continental land mass sedimentation to extensive syn-orogenic clastic (Southworth et al. 2001). sedimentation from the southeast during Ordovician time (Fisher 1976). In the Prince William Forest Park Associated with the shallow marine setting along the area, these metasediments include mica schist, granitic eastern continental margin of the Iapetus were large gneiss, and hornblende gneiss. Northwest of the park deposits of sand, silt, and mud in near-shore, deltaic, these also include phyllonite, mélange, and metasiltstone barrier-island, and tidal-flat areas (fig. 14C). Some of of the Mather Gorge, Yorkshire, Sykesville, and Popes these are present as the Antietam Formation in central Head formations. Oceanic crust caught up in the Virginia (Schwab 1970; Kauffman and Frey 1979; orogenic events now exists as the basic peridotite, Simpson 1991). In addition, huge masses of carbonate gabbro, and pyroxenite (mantle rocks) of the Piney rocks represent a grand platform, thickening to the east, Branch Complex (Drake et al. 1994). that persisted during the Cambrian and Ordovician Periods (545−480 million years ago) (fig. 15A).

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This shallow marine to fluvial sedimentation continued area of Manassas National Battlefield Park, just for a period of about 200 million years during the northwest of Prince William Forest Park. Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian periods, building thick The large faults that formed the western boundaries of layers of sediments. Their source was the highlands that the basins provided an escarpment that was quickly were rising to the east during the Taconic orogeny covered with eroded debris. Magma was intruded into (Ordovician), and the Acadian orogeny (Devonian). The the new strata as sills (sub-horizontal sheets), and nearly Quantico synclinorium underlying Prince William Forest vertical dikes that extend beyond the basins into adjacent Park was compressed during the Taconic orogeny. rocks. After this magma was emplaced approximately Exotic terranes were added to the eastern margin of the 200 million years ago, the region underwent a period of continent, including the Chopawamsic belt. The Acadian slow uplift and erosion. The uplift was in response to orogeny continued the mountain building of the Taconic isostatic adjustments within the crust, which forced the orogeny as the African continent approached North continental crust upwards and exposed it to erosion (fig. America (Harris et al. 1997). 16C). This erosion is evident in the landscape at Prince William Forest Park where deep ravines and ridges of Following the Acadian orogeny, the proto-Atlantic metamorphic rock were carved by rapidly downcutting Iapetus Ocean closed completely during the Late rivers. Paleozoic as the North American continent collided with the African continent, forming the Appalachian Thick deposits of unconsolidated gravel, sand, and silt mountain belt we see today. This mountain-building were shed from the eroded mountains. These were episode, known as the Alleghanian orogeny, is the last deposited at the base of the mountains as alluvial fans major orogeny that affected the Appalachians (fig. 16A). and spread eastward to become part of the Atlantic The rocks were deformed by folds and faults to produce Coastal Plain, which encompasses the eastern third of the Sugarloaf Mountain anticlinorium and the Frederick Prince William Forest Park (Duffy and Whittecar 1991; Valley synclinorium in the western Piedmont, the Blue Whittecar and Duffy 2000; Southworth et al. 2001). The Ridge−South Mountain anticlinorium, and the numerous amount of material that was deposited has been inferred folds of the Valley and Ridge province (Southworth et al. from the now-exposed metamorphic rocks to have been 2001). Many of the faults and folds that resulted from immense. Many of the rocks exposed at the surface must orogenic stresses are exposed today in the landscape have been at least 20 km (≈10 mi) below the surface prior surrounding Prince William Forest Park. to regional uplift and erosion. Erosion continues today with the Potomac, Rappahannock, Rapidan, and During the Alleghanian orogeny, rocks of the Great Shenandoah Rivers, as well as smaller branches such as Valley, Blue Ridge, and Piedmont provinces were the Quantico Creek watershed, and tributaries stripping transported along the North Mountain fault westward the Coastal Plain sediments, lowering the mountains, and onto younger rocks of the Valley and Ridge. The amount depositing alluvial terraces along the rivers, thus shaping of crustal shortening was very large, estimated at the present landscape (fig. 16D). 20−50 %, which translates into 125–350 km (78–217 mi) of movement (Harris et al. 1997). Deformed rocks in the Since the breakup of Pangaea and the uplift of the eastern Piedmont were also folded and faulted, and Appalachian Mountains, the North American plate has existing thrust faults were reactivated as both strike-slip continued to drift toward the west. The isostatic and thrust faults during the Alleghanian orogeny adjustments that uplifted the continent after the (Southworth et al. 2001). Alleghanian orogeny continued at a lesser rate throughout the Cenozoic Period (Harris et al. 1997). Following the Alleghanian orogeny, during the late Triassic, a period of rifting began as the deformed rocks The landscape and geomorphology of the greater of the joined continents began to break apart from about Potomac River and Rappahannock River valleys 230–200 million years ago (fig. 16B). The supercontinent (including the Quantico Creek watershed) in particular Pangaea was segmented into roughly the same continents are the result of erosion and deposition from about the that persist today. This episode of rifting, or crustal middle of the Cenozoic Period to the present, or at least fracturing, initiated the formation of the current Atlantic the last 5 million years. The distribution of flood-plain Ocean and caused many block-fault basins to develop alluvium and ancient fluvial terraces of the rivers and with accompanying volcanism (Harris et al. 1997; adjacent tributaries reflect the historical development of Southworth et al. 2001). both drainage systems. There is little or no evidence that the rivers migrated laterally across a broad, relatively flat The Newark Basin system is a large component of this region. It seems the rivers have cut downward through tectonic setting. Large, stream-fed alluvial fans collected very old, resistant rocks, overprinting their early courses debris shed from the uplifted Blue Ridge and Piedmont (Southworth et al. 2001). The steep ridges and ravines in provinces. These were deposited as non-marine mud and Prince William Forest Park are the result of this sand in fault-created troughs, such as the Culpeper basin downward cutting and overprinting. in the western Piedmont. Many of these rift openings became lacustrine basins and were filled with thick The position, distribution, thickness, and elevation of deposits of silt and sand. The Manassas Sandstone and terraces and the sediments deposited on them along the the Balls Bluff Siltstone represent these deposits in the rivers vary by province and rock type. The elevations of

24 NPS Geologic Resources Division terraces along the rivers show that the gradients of the Given the susceptibility to erosion of the unconsolidated ancient and modern river valleys are similar and suggest deposits throughout the area, dating of recent tectonic that the terraces formed as the result of either eustatic and climatic regimes is problematic. Most of the sea-level drop or uplift (Zen 1997a and 1997b). sediments have eroded away. However, loess deposits (wind-blown silt-sized particles, commonly associated Though glaciers never reached the eastern Virginia area, with glaciation) found on stable landforms near the colder climates of the Ice Ages may have played a role Occoquan, Virginia, indicate that the local transition in the river valley morphology. The periglacial conditions from a colluvial-dominated (rockfall and slope-failure that must have existed at high altitudes intensified processes) to a fluvial-dominated (river and other water weathering and other erosional processes (Harris et al. action) geomorphic regime did not occur in the mid- 1997). The landforms and deposits are probably late Atlantic region until the end of the early Holocene Tertiary to Quaternary, when a wetter climate, sparse (Feldman et al. 2000). Similarly, geologists measure the vegetation, and frozen ground caused increased oxygen isotope ratios in pedogenic clays such as kaolinite precipitation to run into the ancestral river, enhancing (formed from the weathering of muscovite and downcutting and erosion by waterways such as Quantico microcline) to determine the climatic conditions during Creek (Zen 1997a and 1997b). weathering. In the Piedmont province, a cooler climate persisted beyond the Pleistocene glacial stage in North America (Elliott et al. 1997).

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Figure 13: Geologic time scale; adapted from the U.S. Geological Survey (http://pubs.usgs.gov/fs/2007/3015/). Red lines indicate major unconformities between eras. Included are major events in life history and tectonic events occurring on the North American continent. Absolute ages shown are in millions of years.

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Figure 14. Geologic evolution of the Appalachian Mountains in the Prince William Forest Park area. Cross-section view is west to east. (A) First, intrusions of granitic gneiss, metamorphism, and deformation related to the Grenvillian orogeny lasted 60 million years, from 1.1 billion to 950 million years ago. These rocks are found in the Blue Ridge province. (B) Then, continental rifting and volcanic activity in the Grenville terrane (current Blue Ridge province) and deposition of turbidites in deep-water basin to the east (current Piedmont province) lasted about 200 million years, from about 770–575 million years ago. (C) Next, the margin of the continent became stable with carbonate sediments being deposited in quiet water (rocks of the current Great Valley and Frederick Valley). Shelled organisms appeared about 545 million years ago. Then, deep-water sediments were deposited in a basin east of the shelf margin for about 65 million years. Ma, mega- annum (millions of years).

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Figure 15. (A) Following deposition, the stable shelf was destroyed (?) as the Taconic orogeny (B) (480−460 million years ago) elevated the rocks to the east and provided a source for the clastic material that makes up the shale of the Martinsburg Formation. Rocks in the Piedmont province were intruded by plutonic rocks. (C) Then, a thick sequence of sediments was deposited in a deepening Appalachian Basin over a span of 120 million years. Most of these rocks are now found in the Valley and Ridge province. About 370 million years ago magma forming igneous rocks was intruded into rocks near Great Falls. Ma, mega-annum (millions of years).

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Figure 16. (A) About 240 million years ago, the continental tectonic plates of North America and Africa collided, resulting in the Alleghanian orogeny. Many of the folds and faults in rocks west of the Piedmont province are related to this event. (B) About 20 million years later, continental rifting began and lasted for about 20 million years (220−200 million years ago). (C) Thick sequences of sediments were deposited in fault-bounded basins, there was volcanic activity, and the end result was the creation of the Atlantic Ocean. The Culpeper and Gettysburg basins in the western Piedmont are the result of this event. (D) For the last 200 million years, the landscape has eroded and rivers have carried the sediment eastward to deposit the thick strata of the Atlantic Coastal Plain. Diagrams are not to scale and are broadly representative of the tectonic settings. Adapted from Southworth et al. 2001. Ma, mega-annum (millions of years).

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Glossary

This glossary contains brief definitions of technical geologic terms used in this report. Not all geologic terms used are referenced. For more detailed definitions or to find terms not listed here please visit: http://wrgis.wr.usgs.gov/docs/parks/misc/glossarya.html. active margin. A continental margin where significant clay. Clay minerals or sedimentary fragments the size of volcanic and earthquake activity occurs; commonly a clay minerals (>1/256 mm). convergent plate margin. cleavage (rock). The tendency of rock to break along alluvial fan. A fan-shaped deposit of sediment that parallel planes that correspond to the alignment of accumulates where a high-gradient stream flows out of platy minerals. a mountain front into an area of lesser gradient, such concordant. Strata with contacts parallel to the attitude as a valley. of adjacent strata. alluvium. Stream-deposited sediment that is generally conglomerate. A coarse-grained sedimentary rock with rounded, sorted, and stratified. clasts larger than 2 mm in a fine-grained matrix. angular unconformity. An unconformity where the strata continental crust. The type of crustal rocks underlying above and below are oriented differently; generally the continents and continental shelves; having a caused by structural deformation and erosion prior to thickness of 25−60 km (16−37 mi) and a density of deposition of the upper bed. approximately 2.7 grams per cubic centimeter. anticlinorium. A composite anticlinal structure of continental drift. The concept that continents have regional extent composed of lesser folds. shifted in position over Earth (see and use “plate aquifer. Rock or sediment that are sufficiently porous, tectonics”). permeable, and saturated to be useful as a source of continental rise. Gently sloping region from the foot of water. the continental slope to the abyssal plain. ash (volcanic). Fine pyroclastic material ejected from a continental shelf. The shallowly submerged part of a volcano (also see “tuff”). continental margin extending from the shoreline to the asthenosphere. Weak layer in the upper mantle below continental slope with water depths of less than 200 m the lithosphere where seismic waves are attenuated. (656 ft). basement. The undifferentiated rocks, commonly continental shield. A continental block of Earth’s crust igneous and metamorphic, that underlie the rocks of that has remained relatively stable over a long period interest. of time and has undergone only gentle warping basin (structural). A doubly-plunging syncline in which compared to the intense deformation of bordering rocks dip inward from all sides (also see “dome”). crust basin (sedimentary). Any depression, from continental continental slope. The relatively steep slope from the to local scales, into which sediments are deposited. outer edge of the continental shelf down to the more bed. The smallest sedimentary strata unit, commonly gently sloping ocean depths of the continental rise or ranging in thickness from one centimeter to a meter or abyssal plain. two and distinguishable from beds above. convergent boundary. A plate boundary where two bedding. Depositional layering or stratification of tectonic plates are moving together (i.e., a zone of sediments. subduction or obduction). bedrock geology. The geology of underlying solid rock craton. The relatively old and geologically stable interior as it would appear with the sediment, soil, and of a continent (also see “continental shield”). vegetative cover stripped away. cross-bedding. Uniform to highly varied sets of inclined block (fault). A crustal unit bounded by faults, either sedimentary beds deposited by wind or water that completely or in part. indicate distinctive flow conditions. braided stream. A stream, clogged with sediment that cross section. A graphical interpretation of geology, forms multiple channels that divide and rejoin. structure, and/or stratigraphy in the third (vertical) calcareous. A rock or sediment containing calcium dimension based on mapped and measured geological carbonate. extents and attitudes depicted in an oriented vertical carbonaceous. A rock or sediment with considerable plane. carbon, especially organics, hydrocarbons, or coal. crust. The outermost compositional shell of Earth, 10−40 cementation. Chemical precipitation of material into km (6−25 mi) thick, consisting predominantly of pores between grains that bind the grains into rock. relatively low-density silicate minerals (also see chemical sediment. A sediment precipitated directly “oceanic crust” and “continental crust”). from solution (also called “nonclastic”). crystalline. Describes the structure of a regular, orderly, chemical weathering. The dissolution or chemical repeating geometric arrangement of atoms breakdown of minerals at Earth’s surface via reaction debris flow. A rapid and often sudden flow or slide of with water, air, or dissolved substances. rock and soil material involving a wide range of types clastic. Rock or sediment made of fragments or pre- and sizes. existing rocks.

30 NPS Geologic Resources Division deformation. A general term for the process of faulting, isostasy. The process by which the crust “floats” at an folding, shearing, extension, or compression of rocks elevation compatible with the density and thickness of as a result of various Earth forces. the crustal rocks relative to underlying mantle. delta. A sediment wedge deposited at a stream’s mouth isostatic adjustment. The shift of the lithosphere of the where it flows into a lake or sea. Earth to maintain equilibrium among units of varying dike. A tabular, discordant igneous intrusion. mass and density; excess mass above is balanced by a dip. The angle between a structural surface and a deficit of density below, and vice versa. horizontal reference plane measured normal to their joint. A semi-planar break in rock without relative line of intersection. movement of rocks on either side of the fracture disconformity. An unconformity at which the bedding of surface. the strata above and below are parallel. karst topography. Topography characterized by discordant. Having contacts that cut across or are set an abundant sinkholes and caverns formed by the angle to the orientation of adjacent rocks. dissolution of calcareous rocks. divergent boundary. A tectonic plate boundary where lacustrine. Pertaining to, produced by, or inhabiting a the plates are moving apart (e.g., a spreading ridge or lake or lakes. continental rift zone). lamination. The finest stratification or bedding as seen in drainage basin. The total area from which a stream shale and siltstone (syn: lamina or laminae) or the system receives or drains precipitation runoff. formation of laminae. en echelon. Describing parallel or subparallel, closely- landslide. Any process or landform resulting from rapid spaced, overlapping or step-like minor structural mass movement under relatively dry conditions. features in rock, such as faults and tension fractures, lava. Magma that has been extruded out onto Earth’s that are oblique to the overall structural trend. surface, both molten and solidified. eustatic. Relates to simultaneous worldwide rise or fall levees. Raised ridges lining the banks of a stream; may be of sea level in Earth’s oceans. natural or artificial. evaporite. Chemically precipitated mineral(s) formed by limbs. The two sides of a structural fold on either side of the evaporation of solute-rich water under restricted its hingeline. conditions. lineament. Any relatively straight surface feature that can exfoliation. The breakup, spalling, peeling, flaking, etc., be identified via observation, mapping, or remote of layers or concentric sheets from an exposed rock sensing, commonly representing tectonic features. mass due to differential stresses resulting from thermal lithification. The conversion of sediment into solid rock. changes or pressure unloading. lithology. The description of a rock or rock unit, extrusion. The emission of relatively viscous lava onto especially the texture, composition, and structure of the Earth’s surface; also, the rock so formed. sedimentary rocks. extrusive. Of or pertaining to the eruption of igneous lithosphere. The relatively rigid outmost shell of Earth’s material onto the surface of Earth. structure, 50−100 km (31−62 mi) thick, that facies (metamorphic). The pressure-temperature regime encompasses the crust and uppermost mantle. that results in a particular, distinctive metamorphic loess. Silt-sized sediment deposited by wind, generally of mineralogy (i.e., a suite of index minerals). glacial origin. facies (sedimentary). The depositional or environmental mafic. A rock, magma, or mineral rich in magnesium and conditions reflected in the sedimentary structures, iron. textures, mineralogy, fossils, etc. of a sedimentary magma. Molten rock generated within the Earth that is rock. the parent of igneous rocks. fault. A subplanar break in rock along which relative mantle. The zone of Earth’s interior between crust and movement occurs between the two sides. core. formation. Fundamental rock-stratigraphic unit that is matrix. The fine-grained interstitial material between mappable and lithologically distinct from adjoining coarse grains in porphyritic igneous rocks and poorly strata and has definable upper and lower contacts. sorted clastic sediments or rocks. fracture. Irregular breakage of a mineral; also any break meanders. Sinuous lateral curves or bends in a stream in a rock (e.g., crack, joint, fault) channel. frost wedging. The breakup of rock due to the expansion mechanical weathering. The physical breakup of rocks of water freezing in fractures. without change in composition (syn: physical geology. The study of Earth including its origin, history, weathering). physical processes, components, and morphology. member. A lithostratigraphic unit with definable contacts igneous. Refers to a rock or mineral that originated from that subdivides a formation. molten material; one of the three main classes or mesic. Requiring moderate water. rocks—igneous, metamorphic, and sedimentary. metamorphic. Pertaining to the process of intrusion. A body of igneous rock that invades older metamorphism or to its results. rock. The invading rock may be a plastic solid or metamorphism. Literally, “change in form.” magma that pushes its way into the older rock. Metamorphism occurs in rocks through mineral island arc. A line or arc of volcanic islands formed over alteration, genesis, and/or recrystallization from and parallel to a subduction zone. increased heat and pressure.

PRWI Geologic Resources Inventory Report 31 mid-ocean ridge. The continuous, generally submarine, progradation. The seaward building of land area due to seismic, median mountain range that marks the sedimentary deposition. divergent tectonic margin(s) in the world’s oceans. provenance. A place of origin. The area from which the mineral. A naturally occurring, inorganic crystalline solid constituent materials of a sedimentary rock were with a definite chemical composition or compositional derived. range. radioactivity. The spontaneous decay or breakdown of mud cracks. Cracks formed in clay, silt, or mud by unstable atomic nuclei. shrinkage during subaerial dehydration. radiometric age. An age in years determined from nonconformity. An erosional surface preserved in strata radioisotopes and their decay products. in which crystalline igneous or metamorphic rocks recharge. Infiltration processes that replenish underlie sedimentary rocks. groundwater. normal fault. A dip-slip fault in which the hanging wall red beds. Sedimentary strata composed largely of moves down relative to the footwall. sandstone, siltstone, and shale that are predominantly obduction. The process by which the crust is thickened red due to the presence of ferric oxide (hematite) by thrust faulting at a convergent margin. coating individual grains. oceanic crust. Earth’s crust formed at spreading ridges regression. A long-term seaward retreat of the shoreline that underlies the ocean basins. Oceanic crust is 6−7 or relative fall of sea level. km (3−mi) thick and generally of basaltic composition. relative dating. Determining the chronological orogeny. A mountain-building event, particularly a well- placement of rocks, events, fossils, etc. from geological recognized event in the geological past (e.g., the evidence. o Laramide orogeny). reverse fault. A contractional, high-angle (>45 ), dip-slip outcrop. Any part of a rock mass or formation that is fault in which the hanging wall moves up relative to the exposed or “crops out” at Earth’s surface. footwall (also see “thrust fault”). overbank deposits. Alluvium deposited outside a stream rift valley. A depression formed by grabens along the channel during flooding. crest of an oceanic spreading ridge or in a continental paleogeography. The study, description, and rift zone. reconstruction of the physical geography from past ripple marks. The undulating, subparallel, usually small- geologic periods. scale ridge pattern formed on sediment by the flow of paleontology. The study of the life and chronology of wind or water. Earth’s geologic past based on the phylogeny of fossil rock. A solid, cohesive aggregate of one or more minerals organisms. or mineraloids. Pangaea. A theoretical, single supercontinent that roundness. The relative amount of curvature of the existed during the Permian and Triassic Periods (also “corners” of a sediment grain, especially with respect see “Laurasia” and “Gondwana”). to the maximum radius of curvature of the particle. parent (rock). The original rock from which a sandstone. Clastic sedimentary rock of predominantly metamorphic rock or soil was formed. sand-sized grains. passive margin. A tectonically quiet continental margin scarp. A steep cliff or topographic step resulting from indicated by little volcanic or seismic activity. vertical displacement on a fault or by mass movement. pebble. Generally, small, rounded rock particles from 4 seafloor spreading. The process by which tectonic plates to 64 mm in diameter. diverge and new lithosphere is created at oceanic permeability. A measure of the ease or rate that fluids ridges. move through rocks or sediments. sediment. An eroded and deposited, unconsolidated plateau. A broad, flat-topped topographic high of great accumulation of lithic and mineral fragments. extent and elevation above the surrounding plains, sedimentary rock. A consolidated and lithified rock canyons, or valleys (both land and marine landforms). consisting of detrital and/or chemical sediment(s). plate tectonics. The theory that the lithosphere is broken sequence. A major informal rock-stratigraphic unit that up into a series of rigid plates that move over Earth’s is traceable over large areas and defined by a major sea surface above a more fluid aesthenosphere. level transgression-regression sediment package. pluton. A body of intrusive igneous rock. shale. A clastic sedimentary rock made of clay-sized plutonic. Describes igneous rock intruded and particles that exhibit parallel splitting properties. crystallized at some depth in the Earth. silt. Clastic sedimentary material intermediate in size porosity. The proportion of void space (cracks, between fine-grained sand and coarse clay (1/256−1/16 interstices) in a volume of a rock or sediment. mm). Principal of Original Horizontality. The concept that siltstone. A variably lithified sedimentary rock composed sediments are originally deposited in horizontal layers of silt-sized grains. and that deviations from the horizontal indicate post- slickenside. A smoothly polished and commonly striated depositional deformation. surface representing deformation of a fault plane. Principle of Superposition. The concept that sediments slope. The inclined surface of any geomorphic feature or are deposited in layers, one atop another, i.e., the rocks rational measurement thereof (syn: gradient). on the bottom are oldest with the overlying rocks slump. A generally large, coherent mass movement with progressively younger toward the top. a concave-up failure surface and subsequent backward rotation relative to the slope.

32 NPS Geologic Resources Division soil. Surface accumulation of weathered rock and terrane. A region or group of rocks with similar geology, organic matter capable of supporting plant growth and age, or structural style. commonly overlying the parent rock from which it terrestrial. Relating to Earth or Earth’s dry land. formed. theory. A hypothesis that has been rigorously tested spring. A site where water flows out at the surface due to against further observations or experiments to become the water table intersecting the ground surface. a generally accepted tenet of science. strata. Tabular or sheetlike masses or distinct layers (e.g., thrust fault. A contractional, dip-slip fault with a of rock). shallowly dipping fault surface (<45o) where the stratigraphy. The geologic study of the origin, hanging wall moves up and over relative to the occurrence, distribution, classification, correlation, footwall. age, etc. of rock layers, especially sedimentary rocks. topography. The general morphology of Earth’s surface stream. Any body of water moving under gravity flow including relief and location of natural and and confined within a channel. anthropogenic features. strike. The compass direction of the line of intersection trace (fault). The exposed intersection of a fault with that an inclined surface makes with a horizontal plane. Earth’s surface. strike-slip fault. A fault with measurable offset where the trace fossils. Sedimentary structures, such as tracks, relative movement is parallel to the strike of the fault. trails, burrows, etc., that preserve evidence of subduction zone. A convergent plate boundary where organisms’ life activities, rather than the organisms oceanic lithosphere descends beneath a continental or themselves. oceanic plate and is carried down into the mantle. transgression. Landward migration of the sea due to a subsidence. The gradual sinking or depression of part of relative rise in sea level. Earth’s surface. trend. The direction or azimuth of elongation of a linear suture. The linear zone where two continental geological feature. landmasses become joined due to obduction. type locality. The geographic location where a syncline. A fold of which the core contains the stratigraphic unit is well displayed, is formally defined stratigraphically younger rocks; it is generally concave as a typical section, and derives its name. upward. unconformity. A surface within sedimentary strata that synclinorium. A composite synclinal structure of regional marks a prolonged period of nondeposition or extent composed of lesser folds. erosion. tectonic. Relating to large-scale movement and uplift. A structurally high area in the crust, produced by deformation of Earth’s crust. movement that raises the rocks. tectonics. The geological study of the broad structural volcanic. Related to volcanoes; describes igneous rock architecture and deformational processes of the crystallized at or near Earth’s surface (e.g., lava). lithosphere and aesthenosphere (also see “structural water table. The upper surface of the saturated (phreatic) geology”). zone. terraces (stream). Step-like benches surrounding the weathering. The set of physical, chemical, and biological present floodplain of a stream due to dissection of processes by which rock is broken down in place. previous flood plain(s), stream bed(s), and/or valley floor(s).

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References

This section lists references cited in this report as well as a general bibliography that may be of use to resource managers. A more complete geologic bibliography is available from the National Park Service Geologic Resources Division.

Bailey, C.M. 1999. Generalized geologic terrane map of Froelich, A. J.; and B. D. Leavy. 1981. Map showing the Virginia Piedmont and Blue Ridge. mineral resources of the Culpeper Basin, Virginia and http://www.wm.edu/geology/virginia/terranes.html Maryland; availability and planning for future needs. (accessed June 6, 2005) Miscellaneous Investigations Series 1313-B. Reston, VA: U.S. Geological Survey. Brown, G. A. 1980. Water resources of Prince William Forest Park, Virginia. Open-File Report OF 80-0964. Harris, A. G., E. Tuttle, and S. D. Tuttle. 1997. Geology of Reston, VA: U.S. Geological Survey. National Parks. Dubuque, IA: Kendall/Hunt Publishing Company. Dominion Nuclear North Anna, LLC. 2004. North Anna Early Site Permit Application. Report submitted to the Hauser, K., and J. A. Jessop. 1995. Detection of U.S. Nuclear Regulatory Commission (NRC). abandoned mines hazards on government lands using http://www.nrc.gov/reactors/new?licensing/license?re geophysical methods. In Proceedings of the Symposium views/esp/north?anna.html (accessed March, 2005). on the Application of Geophysics to Environmental and Engineering Problems (SAGEEP), comp. R.S. Bell, Drake, A. A., Jr., A. J. Froelich, R. E. Weems, and K. Y. 211−220. Wheat Ridge, CO: Environmental and Lee. 1994. Geologic map of the Manassas Quadrangle, Engineering Geophysical Society. Fairfax and Prince William counties, Virginia. Scale 1:24,000. Geologic Quadrangle Map GQ-1732. Reston, Hopkins, H. T. 1984. Water-resources reconnaissance of VA: U.S. Geological Survey. Prince William Forest Park, Virginia. Water-Resources Investigations WRI 84-4009. Reston, VA: U.S. Duffy, D. F., and G. R. Whittecar. 1991. Geomorphic Geological Survey. development of segmented alluvial fans in the Shenandoah Valley, Stuarts Draft, Virginia. Geological Kauffman, M. E., and E. P. Frey. 1979. Antietam Society of America Abstracts with Programs 23 (1): 24. sandstone ridges; exhumed barrier islands or fault- bounded blocks? Geological Society of America Elder, J. H., Jr. 1989. Soil survey of Prince William County, Abstracts with Programs 11 (1): 18. Virginia. Soil Conservation Service, U.S. Department of Agriculture. Kenworthy, J.P. and V. L. Santucci. 2004. Paleontological Resource Inventory and Monitoring, National Capital Elliott, W. C., S. M. Savin, H. Dong, and D.R. Peacor. Region. National Park Service TIC# D-289. 1997. A paleoclimate interpretation derived from pedogenic clay minerals from the Piedmont Province, Lee, K. Y., and A. J. Froelich. 1989. Triassic-Jurassic Virginia. Chemical Geology 142 (3-4): 201−211. stratigraphy of the Culpeper and Barboursville basins, Virginia and Maryland. Professional Paper 1472. Feldman, S. B., L. W. Zelazny, M. J. Pavich, and H. T. Reston, VA: U.S. Geological Survey. Millard, Jr. 2000. Late Pleistocene eolian activity and post-depositional alteration on the Piedmont of Nelms, D. L., and A. R. Brockman. 1993. Well- northern Virginia. In Regolith in the central and construction, water-level, and ground-water-quality southern Appalachians, ed. G. M Clark, H. H. Mills, data for Prince William County, Virginia, 1992. Open- and J.S. Kite. Southeastern Geology 39 (3-4): 183−198. File Report OF 93-0443. Reston, VA: U.S. Geological Survey. Fisher, G. W. 1976. The geologic evolution of the northeastern Piedmont of the Appalachians. Geological Nelms, D. L., and A. R. Brockman. 1997. Hydrogeology Society of America Abstracts with Programs 8 (2): of, and quality and recharge ages of ground water in, 172−173. Prince William County, Virginia, 1990−91. Water- Resources Investigations WRI 97-4009. Reston, VA: Froelich, A. J. 1989. Maps showing geologic and U.S. Geological Survey. hydrologic factors affecting land-use planning in the Culpeper Basin, Virginia and Maryland. Miscellaneous Nickelsen, R. P. 1956. Geology of the Blue Ridge near Investigations Series 1313-J. Reston, VA: U.S. Harpers Ferry, West Virginia. Geological Society of Geological Survey. America Bulletin 67 (3): 239−269.

Olson, C. G. 1983. Soils and land use tour. Madison, WI: Soil Sciences Society, American Division.

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Pavlides, L. 1990. Geology of part of the northern Virginia Southworth, S., D. K. Brezinski, R. C. Orndorff, K. M. Piedmont. Open-File Report OF 90-0548. Reston, VA: Lagueux, and P. G. Chirico. 2000. Digital geologic map U. S. Geological Survey. of the Harpers Ferry National Historical Park. 1 CD- ROM. Open-File Report OF 00-0297. Reston, VA: U.S. Pavlides, L., J. Pojeta, Jr., M. V. Gordon, Jr., R. L. Parsley, Geological Survey. and A. R. Bobyarchick. 1980. New evidence for the age of the Quantico Formation of Virginia. Geology Southworth, S., C. Fingeret, and T. Weik. 2000. Geologic Boulder 8 (6): 286−290. Map of the Potomac River Gorge: Great Falls Park, Virginia, and Part of the C & O Canal National Schwab, F. L. 1970. Origin of the Antietam Formation Historical Park, Maryland. Open-File Report OF 00- (late Precambrian?, lower Cambrian), central Virginia. 264. Reston, VA: U.S. Geological Survey. Journal of Sedimentary Petrology 40 (1): 354−366. Tollo, R. P., D. Gottfried, and A. J. Froelich. 1988. Field Seal, R. R., II, D. P. Haffner, and A. L. Meier. 1998. guide to the igneous rocks of the southern Culpeper Environmental characteristics of the abandoned Basin, Virginia. In Studies of the early Mesozoic basins of Greenwood Mine area, Prince William Forest Park, the Eastern United States, ed. A. J. Froelich and G. R. Virginia; implications for mercury geochemistry. Robinson, Jr., 391−403. Bulletin 1776. Reston, VA: U.S. Open-File Report OF 98-0236. Reston, VA: U.S. Geological Survey. Geological Survey. Upchurch, G. R., Jr., P. R. Crane, and A. N. Drinnan. Seal, R. R., II, D. P. Haffner, and A. L. Meier. 1999a. 1994. The megaflora from the Quantico locality (Upper Methylmercury in surface waters around an Albian), Lower Cretaceous Potomac Group of Virginia. abandoned gold prospect in the Virginia gold-pyrite Virginia Museum of Natural History, Charlottesville, belt, northern Virginia. Geological Society of America VA. Memoir 4. 64 pages. Abstracts with Programs 31 (3): 66. Whittecar, G. R., and D. F. Duffy. 2000. Geomorphology Seal, R.R., II, D. P. Haffner, A. L. Meier, and C. A. Pollio. and stratigraphy of late Cenozoic alluvial fans, Augusta 1999b. Ground- and surface-water geochemical County, Virginia, U.S.A. In Regolith in the Central and insights into the behavior of limestone amendment at Southern Appalachians, ed. G. M Clark, H. H. Mills, the reclaimed Cabin Branch pyrite mine, Prince and J. S. Kite. Southeastern Geology 39 (3−4): 259−279. William Forest Park, Virginia. Geological Society of America Abstracts with Programs 31 (7): 333. Wynn, J. 2000. A ground electromagnetic survey used to map sulfides and acid sulfate ground waters at the Seiders, V.M., and R. B. Mixon. 1981, Geologic map of the abandoned Cabin Branch Mine, Prince William Forest Occoquan Quadrangle and part of the Fort Belvoir Park, northern Virginia gold-pyrite belt. Open-File Quadrangle, Prince William and Fairfax counties, Report OF 00-360. Reston, VA: U.S. Geological Virginia. Scale 1:24,000. Miscellaneous Investigations Survey. Series I-1175. Reston, VA: U.S. Geological Survey. Zen, E-an. 1997a, The seven-storey river: Simpson, E. L. 1991. An exhumed Lower Cambrian tidal- Geomorphology of the Potomac River channel flat; the Antietam Formation, central Virginia, U.S.A. between Blockhouse Point, Maryland, and In Clastic tidal sedimentology, eds. D. G. Smith, B. A. Georgetown, District of Columbia, with emphasis on Zaitlin, G. E. Reinson, and R. A. Rahmani. Canadian The Gorge complex below Great Falls. Open-File Society of Petroleum Geologists Memoir 16:123−133. Report OF 97-60. Reston, VA: U.S. Geological Survey.

Southworth, S., and D. K. Brezinski. 1996. Geology of the Zen, E-an. 1997b. Channel geometry and strath levels of Harpers Ferry Quadrangle, Virginia, Maryland, and the Potomac River between Great Falls, Maryland, and West Virginia. Bulletin B-2123. Reston, VA: U.S. Hampshire, West Virginia. Open-File Report OF 97- Geological Survey. 480. Reston, VA: U.S. Geological Survey.

Southworth, S., D. K. Brezinski, R. C. Orndorff, P. G. Zen, E-an, and A. Walker. 2000. Rocks and war; geology Chirico, and K. M Lagueux. 2001. Geology of the and the campaign of second Manassas. Shippensburg, Chesapeake and Ohio Canal National Historical Park PA: White Mane Books. and Potomac River Corridor, District of Columbia, Maryland, West Virginia, and Virginia. CD-ROM (Disc 1: A, geologic map and GIS files; Disc 2: B, geologic report and figures). Open-File Report OF 01- 0188. Reston, VA: U.S. Geological Survey.

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Appendix A: Geologic Map Graphic

The following page is a snapshot of the geologic map for Prince William Forest Park. For a poster-size PDF of this map or for digital geologic map data, please see the included CD or visit the Geologic Resources Inventory publications Web page (http://www.nature.nps.gov/geology/inventory/gre_publications.cfm).

36 NPS Geologic Resources Division

Appendix B: Scoping Summary

The following excerpts are from the GRI scoping summary for Prince William Forest Park. The scoping meeting was on April 30−May 2, 2001; therefore, the contact information and Web addresses referred to in this appendix may be outdated. Please contact the Geologic Resources Division for current information.

Executive Summary supply digital geologic databases to accompany this Geologic Resources Inventory (GRI) workshops were mapping. Scott Southworth (USGS-Reston, VA) is the held for National Park Service (NPS) Units in the project leader and main contact. The original PMIS National Capital Region (NCR) over April 30−May 2, (Project Management Information Systems) statement is 2001. The purpose was to view and discuss the park’s available on the NPS intranet (PMIS number 60900); of geologic resources, to address the status of geologic note is that portions of it need to be changed to reflect mapping for compiling both paper and digital maps, and that the source of funding will be Inventory and to assess resource management issues and needs. Monitoring funds and not NRPP. Cooperators from the NPS Geologic Resources Division (GRD), Natural Resources Information Division Desired Enhancements in the Geologic Maps for NCR Parks (NRID), individual NPS units in the region, and the To better facilitate the geologic mapping, Scott United States Geological Survey (USGS) were present for Southworth would like to obtain better topographic the workshop. coverage for each of the NCR units. Tammy Stidham knows that some of these coverages are already available This involved half-day field trips to view the geology of and will supply them to Scott and the USGS. In general, Catoctin Mountain Park, Harpers Ferry NHP, Prince anything in Washington, D.C., proper has 1-meter William Forest Park, and Great Falls Park, as well as topographic coverage, and Prince George's County has another full-day scoping session to present overviews of 1:24,000 coverage. the NPS Inventory and Monitoring (I&M) program, the GRD, and the on-going GRI. Round-table discussions Notes on Prince William Forest Park involving geologic issues for all parks in the National Prince William Forest (PRWI) has the Quantico Capital Region included the status of geologic mapping quadrangle in paper format; however USGS Geologist efforts, interpretation, paleontologic resources, sources Wright Horton has been out to the park and found some of available data, and action items generated from this issues with miscorrelated volcanic units on the map meeting. along South Fork (they shouldn't be volcanics). There was a major reclamation project of the Cabin Branch Geologic Mapping Pyrite Mine back in 1995, and the rehabilitation of the area is continuing still; there are a few Web sites on the Existing Geologic Maps and Publications subject (EPA Web site at After the bibliographies were assembled, a separate http://www.epa.gov/reg3wapd/nps/pdf/cabinbranch.pdf search was made for any existing surficial and bedrock and NPS Web site at geologic maps for the National Capital Region parks. http://www2.nature.nps.gov/grd/distland/prwi_restorati The bounding coordinates for each map were noted and on). The park is preparing "The Geology Trail and entered into a GIS to assemble an index geologic map. Related Sites" as an interpretive trail to showcase some Separate coverages were developed based on scales of the park’s geology. There is also an abandoned gold (1:24,000, 1:100,000, etc.) available for the specific park. mine in the northwest part of the park with partially Numerous geologic maps at varying scales and vintages collapsed mine shafts at Independence Hill. Bob Mixon cover the area. Index maps were distributed to each has worked on the geology of the Joplin quadrangle; workshop participant during the scoping session. Scott and Pete Chirico will check on the status of the open-file report as well as bringing Wright Horton in on Status this project. The index of published geologic maps is a useful reference for the NCR. However, some of these maps are Digital Geologic Map Coverage dated and are in need of refinement and in other places The USGS will supply digital geology in ArcInfo format there are no existing large-scale coverages available. The for all of the NCR parks. GRI staff will take these data USGS began a project to map the Baltimore-Washington, and add the Windows help file and NPS theme manager D.C., area at 1:100,000 scale, and as a result it was capability to the digital geology and will supply it to the brought to their attention that modern, large-scale region to distribute to each park in NCR. geologic mapping for the NCR NPS areas would be beneficial to NPS resource management.

Because of this, the USGS developed a proposal to re- map the NCR at large scale (1:24,000 or greater) and to

PRWI Geologic Resources Inventory Report 39

Other Desired Data Sets for NCR Paleontology Greg McDonald (GRD Paleontologist) would like to see Soils an encompassing, systematic paleontological inventory Pete Biggam (GRD Soil Scientist) supplied the following for the NCR describing the known resources in all parks information in reference to soils for parks: with suggestions on how to best manage these resources. In addition to the parks containing paleo resources in National Capitol Parks - Central is covered by the NACE, according to his current database, the following "District of Columbia" Soil Survey (State Soil Survey are considered "paleo parks" in the NCR: Area ID MD099). It has been mapped, and is currently • Chesapeake & Ohio Canal NHP being refined to match new imagery. An interim digital product is available to us via NRCS, but the "final • George Washington Memorial Parkway certified" dataset most likely will not be available until • Manassas NBP FY03. • Prince William Forest Park National Capitol Parks - Eastern is covered by parts of • Harpers Ferry NHP three soil survey areas: "District of Columbia" (MD099), "Charles County, Maryland" (MD017), and "Prince Geologic Report George's County, Maryland" (MD033). Both Charles A "stand-alone" encompassing report on each park’s County and Prince George's County are currently being geology is a major focus of the GRI. As part of the USGS updated, with Charles County scheduled to be available proposal to map the NCR, they will be summarizing the sometime in calendar year 2002, and Prince George's major geologic features of each park in a report to County sometime within calendar year 2003. accompany their database. It was hoped that after the individual reports are finished a regional physiographic report will be completed for the entire NCR.

40 NPS Geologic Resources Division

List of Attendees for NPS National Capital Region Workshop

NAME AFFILIATION PHONE E-MAIL NPS, Natural Resources [email protected] Joe Gregson (970) 225-3559 Information Division NPS, Geologic Resources [email protected] Tim Connors (303) 969-2093 Division NPS, Geologic Resources [email protected] Bruce Heise (303) 969-2017 Division Lindsay NPS, Geologic Resources [email protected] 202-208-4958 McClelland Division Scott Southworth USGS (703) 648-6385 [email protected] Pete Chirico USGS 703-648-6950 [email protected] 202-342-1443, ext. [email protected] Pat Toops NPS, NCR 212 Cato_resource_management@nps. James Voigt NPS, CATO 301-416-0536 gov 202-342-1443, ext. [email protected] Marcus Koenen NPS, NCR 216 202-342-1443, ext. [email protected] Ellen Gray NPS, NCR 223 Dale Nisbet NPS, HAFE 304-535-6770 [email protected] Suzy Alberts NPS, CHOH 301-714-2211 [email protected] Dianne Ingram NPS, CHOH 301-714-2225 [email protected] Bill Spinrad NPS, CHOH 301-714-2221 [email protected] Debbie Cohen NPS, ANTI 301-432-2243 [email protected] Ed Wenschhof NPS, ANTI/MONO 301-432-2243 [email protected] Ann Brazinski NPS, GWMP 703-289-2541 [email protected] Melissa Kangas NPS, GWMP 703-289-2542 [email protected] Barbara Perdew NPS, GWMP 703-285-2964 [email protected] Barry Wood NPS, GWMP 703-289-2543 [email protected] Marie Sauter NPS, CHOH 301-714-2224 [email protected] Carol Pollio NPS, PRWI 703-221-2176 [email protected] Duane Donnelly- Duane_donnelly- NPS, PRWI 703-221-6921 Morrison [email protected] 202-342-1443, ext. [email protected] Diane Pavek NPS-NRS 209 Chris Jones NPS-WOTR 703-255-1822 [email protected] Doug Curtis NPS-NCR-NRS 202-342-1443, ext.228 [email protected] Brent Steury NPS-NACE 202-690-5167 [email protected] Dave Russ USGS 703-648-6660 [email protected] Tammy Stidham NPS-RTSC 202-619-7474 [email protected] Dan Sealy NPS-GWMP 703-289-2531 [email protected] Sue Salmons NPS-ROCR 202-426-6834, ext. 33 [email protected]

PRWI Geologic Resources Inventory Report 41

Prince William Forest Park Geologic Resources Inventory Report

Natural Resource Report NPS/NRPC/GRD/NRR—2009/086

National Park Service Acting Director • Dan Wenk

Natural Resource Stewardship and Science Associate Director • Bert Frost

Natural Resource Program Center The Natural Resource Program Center (NRPC) is the core of the NPS Natural Resource Stewardship and Science Directorate. The Center Director is located in Fort Collins, with staff located principally in Lakewood and Fort Collins, Colorado and in Washington, D.C. The NRPC has five divisions: Air Resources Division, Biological Resource Management Division, Environmental Quality Division, Geologic Resources Division, and Water Resources Division. NRPC also includes three offices: The Office of Education and Outreach, the Office of Inventory, Monitoring and Evaluation, and the Office of Natural Resource Information Systems. In addition, Natural Resource Web Management and Partnership Coordination are cross-cutting disciplines under the Center Director. The multidisciplinary staff of NRPC is dedicated to resolving park resource management challenges originating in and outside units of the national park system.

Geologic Resources Division Chief • Dave Steensen Planning Evaluation and Permits Branch Chief • Carol McCoy Geosciences and Restoration Branch Chief • Hal Pranger

Credits Author • Trista Thornberry-Ehrlich Review • Phil Cloues and Pat O’Dell Editing • Diane Lane Digital Map Production • Stephanie O’Meara Map Layout Design • John Gilbert

The Department of the Interior protects and manages the nation’s natural resources and cultural heritage; provides scientific and other information about those resources; and honors its special responsibilities to American Indians, Alaska Natives, and affiliated Island Communities. NPS D-54, March 2009 National Park Service U.S. Department of the Interior

Geologic Resources Division Natural Resource Program Center P.O. Box 25287 Denver, CO 80225

www.nature.nps.gov

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