National Park Service

U.S. Department of the Interior

Natural Resource Stewardship and Science

Colonial National Historical Park

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2016/1237
ON THE COVER: The Yorktown Victory Monument was completed in January 1885 and, at nearly 30 m (100 ft) tall, 

overlooks the wide harbor of the York River. Architecturally it was planned and constructed in three parts, with a 

base, a sculptured podium (in the form of a drum), and a column. The whole “is intended to convey, in architectural 

language, the idea, set forth in the dedicatory inscription, that, by the victory at Yorktown, the independence of 

the United States of America was achieved, or brought to final accomplishment.” National Park Service photograph 

courtesy of Dorothy Geyer (Colonial National Historical Park).

THIS PAGE: Local fossils are historically significant to paleontological history. Many species were discovered, described, 

and named from locations in the park. The bivalve (mollusk) Chesapecten jeffersonius was likely the first fossil to be 

described in North America. It was included in Martin Lister’s Historiae Conchyliorum in the late 1600s. National Park 

Service photograph courtesy of Melanie Peters (Geologic Resources Division) taken in August 2005.
Colonial National Historical Park

Geologic Resources Inventory Report

Natural Resource Report NPS/NRSS/GRD/NRR—2016/1237

Trista L. Thornberry-Ehrlich 

Colorado State University Research Associate

National Park Service Geologic Resources Division

Geologic Resources Inventory

PO Box 25287

Denver, CO 80225

June 2016

U.S. Department of the Interior 

National Park Service 

Natural Resource Stewardship and Science 

Fort Collins, Colorado
ii

The National Park Service, Natural Resource Stewardship and Science office in Fort Collins, Colorado, publishes a 

range of reports that address natural resource topics. These reports are of interest and applicability to a broad audience 

in the National Park Service and others in natural resource management, including scientists, conservation and 

environmental constituencies, and the public. 

The Natural Resource Report Series is used to disseminate comprehensive information and analysis about natural 

resources and related topics concerning lands managed by the National Park Service. The series supports the 

advancement of science, informed decision-making, and the achievement of the National Park Service mission. The 

series also provides a forum for presenting more lengthy results that may not be accepted by publications with page 

limitations.

All manuscripts in the series receive the appropriate level of peer review to ensure that the information is scientifically 

credible, technically accurate, appropriately written for the intended audience, and designed and published in a 

professional manner. This report received informal peer review by subject-matter experts who were not directly 

involved in the collection, analysis, or reporting of the data.

Views, statements, findings, conclusions, recommendations, and data in this report do not necessarily reflect views and 

policies of the National Park Service, U.S. Department of the Interior. Mention of trade names or commercial products 

does not constitute endorsement or recommendation for use by the U.S. Government. 

This report is available from the Geologic Resources Inventory website (http://go.nps.gov/gripubs), and the Natural 

Resource Publications Management website (http://www.nature.nps.gov/publications/nrpm/). To receive this report in 

a format optimized for screen readers, please email irma@nps.gov.

Please cite this publication as:

Thornberry-Ehrlich, T. L. 2016. Colonial National Historical Park: Geologic resources inventory report. Natural 

Resource Report NPS/NRSS/GRD/NRR—2016/1237. National Park Service, Fort Collins, Colorado.

NPS 333/133343, June 2016
iii

Contents

Page

Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v

Executive Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

Products and Acknowledgments . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

GRI Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

Geologic Setting and Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Park Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Geologic Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Geologic Significance and Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Geologic Features and Processes . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Fluvial Features and Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Coastal Plain Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Slope Features and Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Paleontological Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Karst Topography and Cornwallis “Cave” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Subsurface Geologic Features and the Chesapeake Bay Impact Crater . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Hydrogeologic System at Yorktown Battlefield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

Geologic Resource Management Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Sea Level Rise, Flooding, and Coastal Vulnerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

Shoreline Erosion, Sediment Transport, and Coastal Engineering Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

Stormwater Management along Colonial Parkway and Upland Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Paleontological Resource Inventory, Monitoring, and Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Geologic Hazards and Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

Groundwater Quantity and Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Karst Landscape Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Yorktown Formation Shrink-and-Swell Clays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Abandoned Mineral and Disturbed Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

Geologic History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Mesozoic Era (252.2 million to 66.0 million years ago)—Origin of the Coastal Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Cenozoic Era (66.0 million years ago to present)—Building and Reshaping the Coastal Plain . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Geologic Map Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Geologic Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Source Maps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

GRI GIS Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

GRI Poster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

Map Unit Properties Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Use Constraints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

Additional References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Geology of National Park Service Areas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

NPS Resource Management Guidance and Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Climate Change Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Geological Surveys and Societies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

US Geological Survey Reference Tools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

Appendix A: Scoping Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
iv

Contents (continued)

2005 Scoping Meeting Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

2014 Conference Call Participants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Appendix B: Geologic Resource Laws, Regulations, and Policies . . . . . . . . . . . . . . . . . . . . . . . . . 81

Page

GRI Poster . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .in pocket

Map Unit Properties Table . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .in pocket
v

Figures

Figure 1. Map of the Chesapeake Bay watershed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Figure 2. Map of the physiographic provinces and subprovinces of Virginia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Figure 3. Generalized cross section and stratigraphic column of the Coastal Plain in Virginia . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Figure 4. Map of terraces on the James-York Peninsula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Figure 5. Geologic time scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Figure 6. Illustration of the evolution of James River and Jamestown Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Figure 7. Map of topographic and fluvial features of Jamestown Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Figure 8. Martin Lister’s 1687 illustration of a fossil shell later known as Chesapecten jeffersonius. . . . . . . . . . . . . . . . . . . . . . . . 10

Figure 9. Illustration of fluvial processes of meandering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Figure 10. Cross section of Jamestown Island . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Figure 11. Illustration of the deposition of the Yorktown Formation (geologic map units Tymh and Tc). . . . . . . . . . . . . . . . . . . . . . 17

Figure 12. Photograph of cliff of Yorktown Formation ca. 1912. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Figure 13. Illustrations of slope movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Figure 14. Illustration of slope creep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Figure 15. Map of the Yorktown Formation within park boundaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Figure 16. Illustration of dissolution sinkhole formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Figure 17. Illustration of fault types. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Figure 18. Map and cross section of the Chesapeake Bay impact structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Figure 19. Map of generalized groundwater flow through hydrogeologic units at Yorktown Battlefield . . . . . . . . . . . . . . . . . . . . 27

Figure 20. Map of flood-vulnerable areas of Jamestown Island. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

Figure 21. Map of shoreline loss at Black Point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

Figure 22. Photographs of shoreline stabilization structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

Figure 23. Aerial image of the Jamestown seawall and the James River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 24. Map of coastal engineering structures along the shorelines in the Jamestown unit. . . . . . . . . . . . . . . . . . . . . . . . . . 37

Figure 25. Map of coastal engineering structures along the shorelines in the Yorktown unit . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Figure 26. Enlarged map of coastal engineering structures along the shorelines in Yorktown . . . . . . . . . . . . . . . . . . . . . . . . . . 38

Figure 27. Photographs of stormwater management structures along the Colonial Parkway . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Figure 28. Photographs of upland erosional features in Colonial National Historical Park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Figure 29. Photograph of exposed rootball at a fallen tree on Jamestown Island. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Figure 30. Probability map of earthquakes with magnitude greater than 5.0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

Figure 31A–C. Illustration of the evolution of the landscape and geologic foundation of Colonial National Historical Park . . . . . . . . . . . 52

Figure 31D–F. Illustration of the evolution of the landscape and geologic foundation of Colonial National Historical Park, continued . . . . . . 53

Figure 32. Paleogeographic maps of North America . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

Page

Plate 1. Maps of Colonial National Historical Park. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . in pocket

Tables

Page

Table 1. Clastic sedimentary rock classification and characteristics. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Table 2. Geologic formation types. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Table 3. Proposed climate effects monitoring plan. . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

Table 4. Climate and depositional setting for map units occurring within Colonial National Historical Park. . . . . . . . . . . . . . . . . . . . 55

Table 5. Geology data layers in the Colonial National Historical Park GIS data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57

vii

Executive Summary

The Geologic Resources Inventory (GRI) is one of 12 inventories funded by the National Park Service 

(NPS) Inventory and Monitoring Program. The Geologic Resources Division of the NPS Natural 

Resource Stewardship and Science Directorate administers the GRI. This report synthesizes discussions 

from a scoping meeting for Colonial National Historical Park (Virginia) on 1 May 2005 and a 

follow-up conference call on 12 November 2014. Scoping participants identified geologic resources 

of significance and geologic resource management issues and needs, as well as the status of geologic 

mapping. This report is a companion document to previously completed GRI GIS data.

This GRI report was written for resource managers 

to support science-informed decision making. It 

may also be useful for interpretation. The report was 

prepared using available geologic information, and the 

NPS Geologic Resources Division conducted no new 

fieldwork in association with its preparation. Sections 

of the report discuss distinctive geologic features and 

processes within Colonial National Historical Park, 

highlight geologic issues facing resource managers, 

describe the geologic history leading to the presentday landscape, and provide information about the GRI 

GIS data. A poster (in pocket) illustrates these data. 

The Map Unit Properties Table (in pocket) summarizes 

report content for each geologic map unit. A glossary 

defines many of the geologic terms used in this text.

Colonial National Historical Park commemorates the 

origins of America across seven historic units:

● historic Jamestowne, the site of America’s first 

permanent English settlement in 1607 and 

Virginia’s capital until 1699;

● Yorktown Battlefield, the scene of the 1781 

culminating battle of the American Revolutionary 

War;

● the 37-km (23-mile) Colonial Parkway;

● Green Spring Plantation;

● Cape Henry Memorial, marking the first landing of 

the colonists in 1607;

● Tyndall’s Point in Gloucester; and

● Swanns Point.

Cape Henry is within the legislative boundary, but not 

the administrative boundary of the park; it is not part of 

the GRI GIS data coverage and is not on the poster. 

The park spans the James-York peninsula between the 

James and York rivers—two major tributaries of the 

Chesapeake Bay watershed. In addition to its historic 

resources and stories, the park encompasses significant 

natural resources, including tidal and nontidal wetlands, 

upland forests, bluffs, open fields, streams, and the 

James and York rivers’ shorelines. These features and 

their geologic foundations strongly influenced the 

history of the area from the prehistoric American Indian 

inhabitants to the European settlements and American 

struggles for independence and unity. 

Colonial National Historical Park is in the Coastal 

Plain physiographic province, a province which 

stretches from Cape Cod to the Mexican border in 

Texas. The coastal plain formed at the same time the 

Atlantic Ocean was forming, more than 180 million 

years ago. Sediments eroded from the Appalachian 

Mountains to build the plain seaward as a thick wedge 

of sediments. In Virginia, the coastal plain is dominated 

by a series of step-wise, riverine terraces. A sloping 

scarp and relatively flat tread compose each terrace, 

the series of which locally decrease in elevation in a 

step-wise manner toward the Chesapeake Bay. During 

fluctuations in sea level more than 20,000 years ago, 

shoreline erosion along major streams and bays created 

the scarps that subsequent slope movements, deep 

incision by stream valleys, and overlapping features have 

obscured, producing a rolling and dissected terrain.

Geologic features and processes include the following:

● Fluvial Features and Processes. The James and 

York rivers and their tributaries are among the 

major natural resources at Colonial National 

Historical Park. Jamestown Island was chosen as 

a settlement because of its defendable position 

nearly surrounded by water. Former traces of the 

meandering river are visible as the swales and ridges 

along the island. The well-drained ridges were the 

first areas that the colonists settled. The shorelines 

within the park are estuarine and the James and 

York rivers are affected by tides of nearly 1 m (3 
viii

ft). Many areas of the park are nearly at sea level. 

Recent mapping of bottom sediments in the James 

River revealed how the currents and waves are 

moving deposits within the river system.

● Coastal Plain Sediments. The sedimentary 

units mapped in the park fall into two broad 

categories. The first are older, marine, fossiliferous 

layers. The second are younger, fluvial-estuarine 

sediments with a wide range in composition and 

spatial distribution. The composition and spatial 

continuity of both types of sediments are complex 

and the subject of much study. Yorktown lends 

its name to the Yorktown Formation. It was the 

excellent exposures near the Moore House that 

caused them to become the official type locality 

of the Moore House Member of the Yorktown 

Formation. This member is rich in shell hash and 

sand.

● Slope Features and Processes. Slope 

movements—the downslope transfer of earth 

materials—occur primarily as small scale slumps 

and slope creep on the park’s steep bluffs and 

ravines. Human activities that disturb earth can 

exacerbate slope movement issues.

● Paleontological Resources. Fossil resources within 

Colonial National Historical Park are historically 

and scientifically significant. The bivalve (mollusk) 

Chesapecten jeffersonius was likely the first fossil to 

be described from North America. It was described 

by Martin Lister in the late 1600s and is now the 

state fossil of Virginia. The Yorktown Formation 

is particularly fossiliferous and yields a wealth of 

information about past climates and ecosystems. 

New fossil discoveries occur regularly in the region. 

● Karst Topography and Cornwallis “Cave”. 

The only cave in the park is Cornwallis “cave”—a 

quarried cavity in the shell hash layers of the Moore 

House Member of the Yorktown Formation. 

Soluble, buried shell hash layers locally dissolve, 

causing subsidence sinkholes to form. Some of 

these sinkholes are large enough to hold water, for 

example Grafton pond and Brackens pond.

● Subsurface Geologic Features and the 

Chesapeake Bay Impact Crater. About 35 million 

years ago, a meteor or comet collided with Earth 

in a location which is now centered beneath 

Cape Charles on the Eastern Shore, adjacent to 

the Chesapeake Bay; today’s Eastern Shore did 

not exist at that time. The resulting crater was a 

depositional center for millions of years afterwards. 

The disturbance to the surrounding sedimentary 

units included the formation of a ring of fractures 

and faults, which are still capable of movement. The 

impact affected the sedimentary history of the area, 

causing juxtapositions of units of differing age and 

composition. Other deep-seated geologic structures 

defy the classic model of the thick, undisturbed 

wedge of sediments of the Coastal Plain. New 

research is revealing the presence of faults in the 

subsurface of the park region. These structures 

have implications for the hydrogeologic system and 

geomorphology of the park.

● Hydrogeologic System at Yorktown Battlefield. 

The importance of the hydrogeologic system at 

Colonial National Historical Park continues to 

be the subject of much study, particularly in light 

of the increase in surrounding development. The 

park is underlain by a complex series of aquifers 

and confining layers with widely varying spatial 

distribution. 

Geologic resource management issues identified during 

the GRI scoping meeting and follow-up conference call 

include the following:

● Sea Level Rise, Flooding, and Coastal 

Vulnerability. Many of the low-lying areas in 

the park contain significant natural and cultural 

resources. Storms occasionally flood vast areas 

of the park. Climate models project that relative 

sea level will continue to rise at Colonial National 

Historical Park. Park resource managers are 

currently seeking a coastal vulnerability index 

study to measure the shoreline’s vulnerability to the 

effects of sea level rise. 

● Shoreline Erosion, Sediment Transport, and 

Coastal Engineering Structures. Where the 

James and York rivers are tidal, such as in the park, 

fluvial processes and sea level rise are intimately 

connected. Rising sea level is causing wetland 

habitats to migrate and exacerbating shoreline loss. 

Loss is most pronounced at Jamestown Island. A 

historic sea wall protects the original settlement, 

but several other places exhibit loss, including 

College Creek, shorelines adjacent to riprap, and 

near bridge crossings. Much of the York River 

corridor is armored with riprap and other shoreline 

engineering structures. Resource managers have 

been active in shoreline management strategies for 

decades. 
ix

● Stormwater Management along Colonial

Parkway and Upland Erosion. The decades-old

stormwater structures along the Colonial Parkway 

are inadequate to handle peak flows and increased

surface runoff associated with adjacent urban

development. Erosion and undercutting threaten

reaches of the parkway. Impervious-surfaces are

a measured indicator of habitat condition whose

threshold is exceeded along the parkway. Resource

managers seek to develop a plan to manage runoff,

erosion, and stormwater along the parkway. In

uplands, increased erosion is threatening cultural

sites.

● Paleontological Resource Inventory, Monitoring,

and Protection. Fossils from Colonial National

Historical Park are historically significant. All

paleontological resources are nonrenewable and

subject to science-informed inventory, monitoring,

protection, and interpretation. A field-based,

park-specific paleontological resource survey 

could provide site-specific information for resource

managers.

● Geologic Hazards and Risks: Slope Movements.

Many of the slope issues in the park follow erosive

storms that also blow over trees releasing sediments

and removing stabilizing roots on park slopes.

Informal trails also cause erosion and degradation

of historic earthworks. Slope wash is particularly 

problematic at College Creek. Resource managers

are seeking to complete a slope monitoring plan.

● Geologic Hazards and Risks: Earthquakes and

Fault Locations. Colonial National Historical Park

is not near a seismic zone; however, the potential

for large earthquakes exist. The probability of a

magnitude-5.0 or greater earthquake within 100

years is 1–2%. This calculation, however, was made

prior to the 2011 earthquake in central Virginia,

which was felt at the park. New faults were revealed

by recent mapping and the park is on a subsiding

side of a fault block associated with the Chesapeake

Bay impact structure. However unlikely, a moderate

earthquake has the potential to damage park

infrastructure, cause liquefaction in the marshy 

places, and/or trigger slope movements.

● Geologic Hazards and Risks: Radon. Radon is

a heavier-than-air, colorless, odorless, radioactive

gas produced by the decay of naturally occurring

uranium and thorium in the sediments beneath

the park. It tends to settle in basements and crawl

spaces. Sediments at the base of the Yorktown

Formation (where it overlies the Eastover 

Formation) commonly contain marine mammal 

bone enriched in phosphate and uranium. High 

levels of radon have been found in dwellings 

built within or just above this contact. Buildings 

and adjacent ground in James City County, near 

Williamsburg located on the Bacons Castle 

Formation, Shirley Alloformation, and Yorktown 

Formation, had elevated radon levels approaching 

the EPA recommended maximum level. 

Remediation of the threat requires monitoring and 

ventilation. 

● Groundwater Quantity and Quality.

Groundwater depletion and brackish water

incursion has been a historic problem in the park.

Groundwater from the area’s shallow aquifer

system can contribute more than half of the flow in

the park area’s streams and a large portion of the

water in the wetlands. Pulses of groundwater help

to flush out the stagnant water in marshes and pore

water. Factors affecting fluctuations of the water

table are complex and include variations in rainfall

and evapotranspiration, hydrogeologic setting, tidal 

fluctuations, sea level rise, and human activity. A 

groundwater monitoring and management plan

could be prepared for Colonial National Historical

Park.

● Karst Landscape Management. Many subsidence

sinkholes occur at the Yorktown Battlefield unit of 

the park and the potential exists that more will

develop.

● Yorktown Formation Shrink-and-Swell Clays.

The weathered sediments of the Moore House and 

Morgarts Beach members of the Yorktown

Formation contain clay and silt that act as an

aquitard to percolating groundwater and have high

shrink-and-swell potential. The change in volume

associated with wet clay expanding and then drying

can damage roads, trails, building foundations, and

other infrastructure.

● Abandoned Mineral and Disturbed Lands.

Cornwallis cave is the only abandoned mineral and 

disturbed lands feature that occurs in the NPS

database for this park. Other small features are

within park boundaries. Park staff are requesting a

condition assessment of Cornwallis “cave” (quarry)

particularly the roof as large fragments of rock fall

to the floor. Superfund sites and abandoned 

borrow pits near the park may impact resources 

within the park. 

xi

Products and Acknowledgments

The NPS Geologic Resources Division partners with institutions such as Colorado State University, 

the US Geological Survey, state geological surveys, local museums, and universities to develop GRI 

products. This chapter describes those products and acknowledges contributors to this report.

GRI Products

The objective of the Geologic Resources Inventory is 

to provide geologic map data and pertinent geologic 

information to support resource management and 

science-informed decision making in more than 

270 natural resource parks throughout the National 

Park System. To realize this objective, the GRI team 

undertakes three tasks for each natural resource park: 

(1) conduct a scoping meeting and provide a summary 

document, (2) provide digital geologic map data in a

geographic information system (GIS) format, and (3)

provide a GRI report (this document). These products

are designed and written for nongeoscientists.

Scoping meetings bring together park staff and geologic 

experts to review and assess available geologic maps, 

develop a geologic mapping plan, and discuss geologic 

features, processes, and resource management issues 

that should be addressed in the GRI report. Following 

the scoping meeting, the GRI map team converts the 

geologic maps identified in the mapping plan to digital 

geologic map data in accordance with the GRI data 

model. After the map is completed, the GRI report team 

uses these data, as well as the scoping summary and 

additional research, to prepare the GRI report. 

The compilation and use of natural resource 

information by park managers is called for in the 1998 

National Parks Omnibus Management Act (section 

204), 2006 National Park Service Management 

Policies, and the Natural Resources Inventory and 

Monitoring Guideline (NPS-75). The “Additional 

References” chapter and Appendix B provide links to 

these and other resource management documents and 

information.

Additional information regarding the GRI, including 

contact information, is available at http://go.nps.gov/gri. 

The current status and projected completion dates of 

products are available at http://go.nps.gov/gri_status.

Acknowledgments

The GRI team thanks Rick Berquist and the rest of the 

staff at the Virginia Division of Geology and Mineral 

Resources. 

Review

Jason Kenworthy (NPS Geologic Resources Division)

Courtney Schupp (NPS Geologic Resources Division)

Amanda Babson (NPS Northeast Region)

Rick Berquist (Virginia Division of Geology and 

Mineral Resources)

Vincent Santucci (NPS Geolgoic Resources Division)

Dorothy Geyer (Colonial National Historical Park)

Editing

Rebecca Port (NPS Geologic Resources Division)

Report Formatting and Distribution

Jason Kenworthy (NPS Geologic Resources Division)

Rebecca Port (NPS Geologic Resources Division)

Source Maps

C. R. Berquist (Virginia Division of Geology and

Mineral Resources)

GRI GIS Data Production

Stephanie O’Meara (Colorado State University)

James Winter (Colorado State University)

Georgia Hybels (Colorado State University)

GRI Poster Design

Georgia Hybels (Colorado State University)

GRI Poster Editing

Georgia Hybels (Colorado State University)

Rebecca Port (NPS Geologic Resources Division)

Jason Kenworthy (NPS Geologic Resources Division)

1

Geologic Setting and Significance

This chapter describes the regional geologic setting of Colonial National Historical Park and 

summarizes connections among geologic resources, other park resources, and park stories.

Park Setting

Colonial National 

Historical Park was 

originally authorized 

as a national 

monument on June 

3, 1930. It became 

a national historical 

park on June 5, 1936 

and now receives 

about three million 

visitors per year. 

The park includes 

more than 3,500 ha 

(8,600 ac) of natural 

and cultural space 

spread across seven 

units along and 

including the 37-km 

(23-mi) -long and 

150-m (500-ft) -wide 

Colonial Parkway in 

James City and York 

counties (plate 1). 

Elevations within 

the park range from 

sea level to 38 m 

(120 ft) above sea 

level (Lookingbill 

et al. 2012). The 

park straddles the 

peninsula between 

the James and 

York rivers, spans 

two subwatersheds, and is within the southern part 

of the Chesapeake Bay watershed (fig. 1). The park 

encompasses significant natural resources, including 

about 810 ha (2,000 ac) of tidal and nontidal wetlands, 

405 ha (1,000 ac) of open fields, and 65 km (40 mi) of 

shorelines along streams and the James and York rivers 

(Rafkind 1990). 

The Historic Jamestowne unit, the site of America’s first 

permanent English settlement in 1607 and Virginia’s 

capital until 1699, anchors the western end of the 

Colonial Parkway unit. Yorktown Battlefield, the 

scene of the 1781 culminating battle of the American 

Revolutionary War, is at the eastern terminus (plate 1). 

The Colonial Parkway passes through Williamsburg, 

capital of Virginia from 1699 to 1776. The Green 

Spring Plantation unit, site of a battle that occurred 

prior to the military engagement at Yorktown, is 3 km 

(2 mi) northwest of Jamestown. This was the home 

of an influential 17th century governor of Virginia, 

Figure 1. Map of the Chesapeake Bay watershed. Colonial National Historical Park (green) 

straddles the boundaries between two subwatersheds on the James-York Peninsula. 

Graphic is adapted from figure 2.3 in Lookingbill et al. (2012) by Trista L. Thornberry-Ehrlich 

(Colorado State University). Basemap by Tom Patterson (National Park Service), available at 

http://www.shadedrelief.com/physical/index.html (accessed 18 September 2014).
2

Sir William Berkeley (US Army Corps of Engineers 

2002). The Cape Henry Memorial unit in Virginia 

Beach marks the approximate site of the first landing of 

Jamestown colonists in 1607. The military fortifications 

of the Tyndall’s Point unit are across the York River in 

Gloucester County. Another unit, at Swanns Point, lies 

in Surry County across the James River from Jamestown 

Island. The park also features Civil War era history; 

Yorktown and Williamsburg were sites of battles during 

the Peninsula Campaign. Yorktown National Cemetery 

was established for Civil War interments. 

Geologic Setting

Five distinct physiographic provinces encompass 

Virginia, from west to east: Appalachian Plateaus, 

Valley and Ridge, Blue Ridge, Piedmont, and Coastal 

Plain provinces (fig. 2). Colonial National Historical 

Park is in the Coastal Plain physiographic province—a 

relatively flat landscape underlain by a wedge-shaped 

sequence of more than 2,400 m (8,000 ft) of soft, mostly 

unconsolidated sediments (fig. 3) that were eroded 

from the bedrock highlands to the west (Bailey 1999). 

Large streams and rivers in the Coastal Plain province, 

including the James, Rappahannock, and Potomac 

rivers, continue to transport sediment and build the 

coastal plain eastward onto the submerged Continental 

Shelf province which extends another 120 km (75 

miles) into the Atlantic Ocean. The boundary between 

the Piedmont and Coastal Plain provinces is called 

the “fall line”. It is a low, east-facing escarpment that 

parallels the Atlantic coastline from New Jersey to the 

Carolinas. An escarpment is a long, steep slope that 

faces one direction breaking the continuity of the land 

by separating two adjacent surfaces and is commonly 

produced by erosion or faulting. This erosional scarp, 

80 km (50 mi) northwest of Colonial National Historical 

Park, formed where the hard, resistant metamorphic 

rocks of the Piedmont and the unconsolidated 

sediments of the Atlantic Coastal Plain, approximately 

120 to 140 km (75 to 90 mi) inland from the coast, were 

Figure 2. Map of the physiographic provinces and subprovinces of Virginia. Colonial National Historical Park (green 

oval) is within the Coastal Plain province, straddling the Upland and Lowland subprovinces on the James-York 

Peninsula. Graphic is adapted from Bailey (1999) by Trista L. Thornberry-Ehrlich (Colorado State University). Basemap 

by Tom Patterson (National Park Service), available at http://www.shadedrelief.com/physical/index.html (accessed 18 

September 2014).
3

Figure 3. Generalized cross section and 

stratigraphic column of the Coastal Plain in 

Virginia. Colonial National Historical Park 

is within the Coastal Plain province, and 

contains all of the geologic units depicted 

in this graphic except the Charles City and 

Chuckatuck alloformations (gray shaded areas). 

The approximate extent (as per fig. 4) of the 

park is shown by a green bar above the cross 

section. An unnamed flat and scarp separate 

the Shirley and Sedgefield Member of the 

Tabb Alloformation underlain by the Elsing 

Green. This unit is a recent addition to the 

understanding of Virginia’s coastal plain (Rick 

Berquist, written communication, 24 August 

2015; Powars et al. 2015). Red text refers to 

regional scarps. Green text refers to terrace 

“treads”. Wavy lines between units indicate 

unconformable contacts. Boundary ages are 

millions of years ago. The base of the Miocene 

extends beyond the units depicted on this 

graphic. Information about the sedimentary 

units and their depositional environments are 

detailed in table 4 and the Map Unit Properties 

Table. Locations are shown in figure 4. Graphics 

are adapted from figure 3 of Johnson (2007) and 

figure 5 in Brockman et al. (1997), by Trista L. 

Thornberry-Ehrlich (Colorado State University). 
4

juxtaposed. The fall line is the site of many waterfalls 

that yielded flume- and waterwheel-powered industries 

in colonial times and thus became the location of major 

cities such as Philadelphia, Baltimore, Washington DC, 

and Richmond (US Geological Survey 2000). The park 

includes areas of the Upland and Lowland subprovinces 

of the Coastal Plain province. Elevations in these 

subprovinces range from 20 to 80 m (60 to 250 ft) and 0 

to 20 m (0 to 60 ft), respectively (Bailey 1999). 

A succession of riverine, erosional terraces composes 

the landscape of Virginia’s coastal plain. Each terrace, 

composed of a gently sloping scarp and relatively 

flat “tread” or level area referred to as flats or plains, 

Figure 4. Map of terraces on the James-York Peninsula. Colonial National Historical Park (pink area) spans several 

treads or flat areas among erosional scarps. The elevations of the base of the scarps are as follows: Surry scarp is 29m 

(95 ft); Ruthville scarp is 24 m (79 ft); Lee Hall scarp is 19 m (62 ft); Kingsmill scarp is 14 m (46 ft); Suffolk scarp is 8 m 

(26 ft); unnamed scarp is 12 m (38 ft); Big Bethel scarp is 5.5 m (18 ft); and Fort Eustis scarp is 3.5 m (11 ft). Yellow lines 

and text refers to regional scarps. Green text in black boxes refers to terrace “treads”. Graphic is adapted from figure 

2 of Johnson (2007) by Trista L. Thornberry-Ehrlich (Colorado State University) using ESRI World Imagery basemap, 

(accessed 7 October 2014) and information from Powars et al. (2015) and Rick Berquist (written communication, 24 

August 2015). 
5

decreases in elevation in a step-wise manner toward 

the Chesapeake Bay (figs. 3 and 4). The local succession 

from west to east are the Norge upland, Surry scarp, 

Lackey plain, Ruthville scarp, Grove plain, Lee Hall 

scarp, Grafton plain, Kingsmill scarp, Huntington flat, 

Suffolk scarp, unnamed flat and scarp (Elsing Green), 

Todds (Hornsbyville) flat, Big Bethel scarp, Hampton 

flat, Fort Eustis scarp, and the Plum Tree Island ridges 

(Johnson 2007; Rick Berquist, Virginia Division of 

Geology and Mineral Resources, geologist, written 

communication, 24 August 2015; Powars et al. 2105). 

Park areas or the parkway are located on most of these 

features (figs. 3 and 4). The Surry scarp is one of the 

most extensive landforms on the coastal plain extending 

along the Atlantic coast (Johnson et al. 2001a). During 

the past 2.6 million years or more (late Pliocene and 

Pleistocene epochs; see fig. 5), shoreline erosion along 

major streams and bays created the scarps, which vary 

in height from less than 2 m (6 ft) to more than 20 m (66 

ft). Slope movements, deep incision by stream valleys, 

and overlapping features have obscured the terraces 

and produced a rolling and dissected terrain (Johnson 

2007).

The park is 8 km (5 mi) northwest of the open 

Chesapeake Bay on the estuarine York River and

24 km (15 mi) upstream of the bay on the James River. 

The landscape ranges from tidally influenced marshy 

lowlands and wetlands of Jamestown Island, to eroded 

rolling hills of the interior of the James-York Peninsula, 

to deeply scoured bluffs above the York River at 

Yorktown. 

Geologic Significance and Connections

The geologic framework of Colonial National 

Historical Park has strongly affected the history and 

natural features of the region. In 1607, English settlers 

established a colony on a defensible upland site on the 

otherwise low-lying Jamestown Island. At that time, the 

region was in the midst of a prolonged drought (Stahle 

2005). The colonists were also challenged with brackish 

water, prolific insects, starvation, and sometimes-hostile 

relations with American Indians. However, despite these 

issues, the colony persisted and today is considered a 

fundamental piece of American history. The story of the 

colony stretched through the American Revolutionary 

and Civil wars when the area was a strategic target. The 

region’s fossils played a role in the history of North 

American paleontology. Today, the geology contributes 

to the development of soils and together with landforms 

supports a series of natural habitats and ecosystems in 

an otherwise urban landscape, and continues to shape 

the human and natural stories at Colonial National 

Historical Park.

Prehistory and European Colonization

Humans lived in coastal Virginia for thousands of 

years prior to the arrival of the European colonists, as 

evidenced by myriad archeological sites, including a 

hearth at Black Point (Thornberry-Ehrlich 2005). When 

humans first migrated to southeastern Virginia at least 

10,000 years ago, sea level was approximately 70 m (230 

ft) lower than at present, meaning that what is now 

Jamestown Island was part of the mainland and perched 

more than 30 m (100 ft) above the James River (Johnson 

et al. 1995; Johnson 2007; Vanasse Hangen Brustlin, 

Inc. 2009). A series of ridges separated by freshwater 

streams emerged from the western side of the island 

(Johnson et al. 1995). At this time, the James River was 

not tidally influenced; it was completely freshwater and 

flowed through a deeply entrenched valley. Sea level 

began to rise after the end of the last major glaciation, 

approximately 12,000 years ago. By about 5,000 years 

ago, local sea level was only about 10 m (33 ft) below 

its present level and the lower James River began to 

be affected by tides. As brackish marshes replaced the 

lowest-lying lands, human occupation moved further 

upslope (fig. 6) (Johnson et al. 1995). Throughout this 

time of sea level rise, James River tributaries were a 

source of freshwater for local inhabitants, including the 

Powhatan Indians around Jamestown Island (US Army 

Corps of Engineers 2002; Johnson 2007). Abundant 

middens suggest that human settlements concentrated 

in places underlain by sand and gravel, rather than 

wetland muck (GRI conference call participants, 12 

November 2014). 

Thousands of years later, after landing at Cape Henry 

at the mouth of Chesapeake Bay, English colonists 

sailed three ships into the bay, searching for suitable 

sites for a settlement. On 13 March 1607, they landed 

at Jamestown Island and the “settlement era”, which 

would last until 1745, began (Vanasse Hangen Brustlin, 

Inc. 2009). Colonists also took advantage of uplands 

underlain by the Lynnhaven Member of the Tabb 

Alloformation (geologic map unit Qtl) such as the 

western end of Church Point ridge (fig. 7) where they 

built James Fort and Jamestowne (Johnson 2007). At this 

time, Jamestown island was connected to the mainland 

by a narrow isthmus near Back River, but was otherwise 
6

Figure 5. Geologic time scale. Geologic units occurring within Colonial National Historical Park are included. The 

divisions of the geologic time scale are organized stratigraphically, with the oldest divisions at the bottom and the 

youngest at the top. GRI map abbreviations for each time division are in parentheses. Boundary ages are millions of 

years ago (MYA). National Park Service graphic using dates from the International Commission on Stratigraphy

(http://www.stratigraphy.org/index.php/ics-chart-timescale; accessed 13 August 2014) and data from Berquist (2015).
7

surrounded by open water and almost impassable 

marshes. Sea level was 0.9 to 0.6 m (3 to 2 ft) lower than 

at present (Johnson et al. 1995). The combination of 

abundant timber, open water for navigation and trade, 

defensible uplands, and a nearshore, deepwater thalweg 

for anchorage made the island suitable for habitation. 

Freshwater came from shallow wells dug within James 

Fort (Johnson 2007). 

Figure 6. Illustration of the evolution of James River and Jamestown Island. Approximately 12,500 years ago, around 

the end of the last major global glaciation, sea level was much lower and the James River flowed across its floodplain 

in a narrow, incised channel. As sea level began to rise due to glacial ice melting, the river became wider. Eventually, 

sea level was high enough that tides began to affect the James River. By the time European colonists arrived in 1607, 

Jamestown Island was only connected to the mainland by a narrow isthmus. Graphic by Trista L. Thornberry-Ehrlich 

(Colorado State University) adapted from figure 20 of Johnson (2007). 
8

As described in the “Fluvial Features and Processes” 

section, archeological excavations on Jamestown Island 

revealed that the colonists used abundant local natural 

resources for brick making, masonry, goldsmithing, 

blacksmithing, glass making, and crafting tobacco pipes 

and other pottery (Kelso and Straube 2004). Colonists 

likely used sand (e.g., Qb) for iron casting, and clay (e.g., 

Qtl) for pottery and brick making at locations such as 

Indian Field Creek, the kiln at Greenspring, and William 

Rogers’s kilns at Yorktown. William Rogers was the 

“poor potter” who operated one of the largest known 

pottery factories in colonial America and ultimately 

helped undermine the British economic hold over the 

colonies (National Park Service 2014b). Construction 

of the kilns themselves also required natural resources; 

large amounts of earth had to be mounded in place 

for insulation (GRI conference call participants, 12 

November 2014). Exact locations of raw materials 

quarries remain largely unknown, but could be a 

potential project for the Geoscientists-in-the-Parks 

Program (http://go.nps.gov/gip). Despite the natural 

richness, the settlement was largely abandoned in 1699 

after several fires and also possibly because of brackish 

water incursions caused by droughts and changing 

water levels (Stahle 2005; Thornberry-Ehrlich 2005; 

Thomson 2009). 

Some of the earliest land use in the park region was 

tobacco plantations and other agriculture. Successful 

settlement transitioned the early colony into the 

“plantation period”, which lasted from about 1745 

until 1892. Plantations such as Greenspring relied on 

springs for fresh water, which tended to emerge where 

groundwater flowing along impervious layers contacted 

the ground surface (Carson 1954; Speiran and Hughes 

2001; GRI conference call participants, 12 November 

2014). During the plantation period, colonists removed 

many of the trees on Jamestown Island and excavated 

irrigation ditches (Vanasse Hangen Brustlin, Inc. 2009). 

Without having properly fertilized and cared for the 

Figure 7. Map of topographic and fluvial features of Jamestown Island. Colonial National Historical Park (pink outline) 

encompasses the entire island which includes uplands: Church Point ridge, Confederate Ruins ridge, Passmore Creek 

ridges, and Goose Hill, as well as lowlands: Back River marsh, Pitch and Tar swale, and Passmore Creek. Red dashed line 

is the trace of the Black Point scarp which ends at Black Point, an area of shoreline loss. Map is adapted from figure 

15 of Johnson (2007) by Trista L. Thornberry-Ehrlich (Colorado State University) using ESRI World Imagery basemap, 

(accessed 13 October 2014).
9

soils, most plantations suffered widespread depletion of 

soil nutrients after several years. Glauconite (blue clay) 

and fossil shell material were mined from the Yorktown 

Formation (Tymh and Tc) to use as soil additives to 

boost tobacco production (Thornberry-Ehrlich 2005). 

Bellefield, a colonial plantation on the York River, part 

of which is within the park, was a site where marl and 

greensand were mined to put on agriculture fields 

(Rogers 1884). Greensand is shallow marine sediment 

that contains abundant rounded greenish grains or 

glauconies which consist of a mixture of clay minerals, 

such as smectite and glauconite. These additives were 

rich in phosphoric acid, sulphuric acid, silicic acid, 

sand, potash, magnesia, iron oxide, lime (carbonate), 

water, and other trace minerals; they increased the 

water retentive properties of the soil (Krijgsman 2001). 

Iron-rich minerals, such as limonite and goethite, in 

the ledge-forming layers at the top of the Yorktown 

Formation and some overlying formations (Tymh

and Tc) were removed in large slabs as iron ore by 

colonists and slaves and transported to iron furnaces 

(Thornberry-Ehrlich 2005). These iron-rich minerals 

formed as a type of residual cement or precipitate 

during calcium carbonate dissolution. The iron 

precipitated where carbonate shell material buffered 

the acidic water flowing downward from overlying 

sediments (Speiran and Hughes 2001). 

Colonists also utilized the hydrogeologic system; 

flowing water was a source of power for colonial 

industry. Several of the park’s waterways were dammed 

for use by the Jones, Augustus Moore, and Wormley 

mills in the park. Remnants of these mills are preserved 

today as mill ponds and earthen dams (ThornberryEhrlich 2005). 

Geologic Features and War

Geologic features and processes of the James-York 

Peninsula impacted military strategy during the 

American Revolutionary and Civil wars. The proximity 

to two major rivers flowing into the Chesapeake Bay 

and out to the Atlantic Ocean made this location 

strategically valuable.

During the Revolutionary War, the British occupied 

Jamestown Island before losing it to the colonial forces. 

The deepwater thalweg of the James River made it 

an ideal location to outfit ships for combat (Vanasse 

Hangen Brustlin, Inc. 2009). However, when water 

travel was not an option due to inclement weather 

or other military actions (e.g., naval blockades), the 

peninsula became a trap. Such was the case for the 

British General Cornwallis and nearly 7,000 troops that 

were besieged by American and French troops at the 

end of the James-York Peninsula. The colonial forces 

dug progressively closer trenches and constructed 

earthworks in the unconsolidated to loosely 

consolidated coastal plain sediments (geologic map 

units Tymh, Tc, Qw, Qeg, and Qsh) at Yorktown. A fleet 

of French warships came up behind the peninsula and 

cut off a water-based escape route. Trapped against the 

bluffs of Yorktown and unable to cross the York River to 

Gloucester, General Cornwallis was forced to surrender 

on 19 October 1781. He signed terms at Moore House 

in the penultimate confrontation of the American 

Revolutionary War (Lowry 1989).

Cornwallis “cave,” a cavern created by stone quarrying 

for building material, was once believed to be the 

“grotto” into which British General Cornwallis retreated 

to avoid bombardment during the Revolutionary War 

battle. Subsequent research suggested this is likely a 

legend. The cave was used for potato storage during 

colonial times and later for storage of Confederate 

munitions during the American Civil War in 1862. 

Large, visible recesses were cut into the front wall by 

Confederate forces to install support beams for a plank 

roof and walls that were then covered with earth to 

protect the munitions from Union warships offshore. 

The gated cave has since fallen into disrepair as a result 

of the natural processes of weathering and erosion and 

lack of maintenance (Johnson 2007).

The land surface also influenced military tactics. As 

described in the “Karst Topography and Cornwallis 

Cave” section, dissolution in calcium carbonate-rich 

sediments created a complex surface pockmarked by 

sinkholes, depressions, and slumps (Brockman et al. 

1997). General Washington entrenched his forces along 

natural narrow ravines and karst depressions to tighten 

his military lines around the British forces. 

Seeps and springs are other common topographic 

features and occur where the water table intersects the 

land surface. Washington’s headquarters were located 

near a spring. Nearly 100 years after the Revolutionary 

War, Confederate troops dammed some of the spring 

drainages to flood the narrow valleys and create deep 

moats to protect their positions against advancing 

Union forces (Brockman et al. 1997). 
10

Confederates also occupied Jamestown Island in 

an attempt to control access to the James River, 

but were forced to evacuate during Major General 

McClellan’s Peninsula Campaign. The island then 

became a rendezvous for people escaping slavery 

(Vanasse Hangen Brustlin, Inc. 2009). 

In addition to its strategic location, the iron-rich 

sediments atop the Yorktown Formation (Tch, 

Tymh and Tc) on the James-York Peninsula sparked 

some local interest during the American Civil War 

(Thornberry-Ehrlich 2005). Slabs of iron-cemented 

sand and limonite littered the ground, having eroded 

from the hillsides (Rick Berquist, Virginia Division of 

Geology and Mineral Resources, geologist, written 

communication, 24 August 2015). The relative lack of 

iron resources available to the Confederate States of 

America limited industry and military manufacturing 

compared to the United States of America. This 

meant any local sources were incredibly valuable.

Historically Significant Paleontological 

Resources

The fossiliferous marine shell beds (“shell hash”) 

of the coastal plain of Virginia were utilized by 

American Indians prior to Europeans’ arrival in 

1607. Paleoindians (the first people who entered and 

inhabited the American continents during the late 

Pleistocene) used fossil shark (Carcharodon sp.) teeth 

as scrapers and used scallop (Chesapecten sp.) shells for 

drinking vessels (Johnson 2007). 

Some of the earliest colonial uses of the resources were 

for making lime for mortar and in agriculture (Rogers 

and Rogers 1837). Other uses included aggregate for 

road surfaces and quarrying coquina (layers made up 

entirely of shells) for building material. Yorktown’s 

Grace Episcopal Church was constructed of coquina in 

1697 (Roberts 1932).

Fossils from the Yorktown Formation (geologic map 

units Tymh and Tc) once lived in open marine, lagoon or 

other restricted marine, and barrier environments. They 

first appeared in scientific literature in the 1680s as part 

of Martin Lister’s Historiae Conchyliorum (“history 

of shells”). Due to their incredible preservation and 

appearance, they were initially identified as modern 

shells, not fossils. The fossil scallops may be as large 

as dinner plates whereas scallop shells of today are 

roughly palm-sized. Lister’s illustration (fig. 8) likely 

represents the earliest published reference to a fossil 

from North America and this fossil, the mollusk 

Chesapecten jeffersonius, was named the Virginia state 

fossil in 1993 (Ward and Blackwelder 1975; Ray 1987; 

Kenworthy and Santucci 2006; Ward 2008; Tweet et al. 

2014). Revolutionary War General Benjamin Lincoln, 

who served at the siege of Yorktown, described the 

fossil beds at the bluffs in detail (Lincoln 1783). German 

naturalist Johann David Schöpf, serving as a doctor for 

the British army, noted prolific shell beds in the vicinity 

(Roberts 1932; Ray 1983; Tweet et al. 2014). Fossils 

collected from the Colonial National Historical Park 

area grace museums such as the Smithsonian National 

Museum of Natural History in Washington, DC, the 

Laboratoire de Géologie in Paris, France, and the 

Natural History Museum in London, United Kingdom 

among many others (Tweet et al. 2014). 

Soils

Soils form in a complex process that is in part 

controlled by the underlying geology. Soils in the park 

support the growth of several locally or globally rare 

forest types: Coastal Plain Mesic Calcareous Ravine 

Forest (found on ravine slopes that cut through Tertiary 

shell hash of the Yorktown Formation [geologic map 

units Tymh and Tc]), Coastal Plain Dry Calcareous 

Figure 8. Martin Lister’s 1687 illustration of a fossil shell later 

known as Chesapecten jeffersonius. Lister’s illustration likely 

represents the earliest published reference to a fossil from 

North America and was named the Virginia state fossil in 

1993. Illustration reproduced in Ward and Blackwelder (1975).
11

Forest (forms over calcareous sediments on southeast 

and southwest aspect slopes), and Tidal Bald Cypress 

Forest/Woodland (forms in a transition zone between 

open tidal water and tidal marsh at Swanns Point and 

Jamestown Island) (Lookingbill et al. 2012). Soils are 

not described in detail in this report. An NPS Soil 

Resource Inventory product for Colonial National 

Historical Park was updated in 2013 and is available at 

https://irma.nps.gov/App/Reference/Profile/1048845/.

Ecosystem Connections

The geology, soils, and landforms work in concert along 

with other factors including climate to create habitats 

that support biodiversity in the park. The park preserves 

these habitats amidst the heavily urbanized southeast 

region of Virginia. Freshwater, uplands, tidal marshes, 

estuaries, beaches, and bluffs ecosystems are present 

within Colonial National Historical Park (Stevens et al. 

2010). Four dominant habitat types are present within 

the park: forest, grassland, nontidal wetland, and tidal 

wetland; current condition assessments rate these 

habitats as degraded or fair (Lookingbill et al. 2012).

Colonial National Historical Park has the second 

highest number of rare, threatened, and/or endangered 

species in National Park Service units of Virginia 

(Shenandoah National Park has the highest number) 

(Rafkind 1990; Vanasse Hangen Brustlin, Inc. 2009; 

Lookingbill et al. 2012). Lookingbill et al. (2012) 

presents detailed information about species of 

concern at the park which include sensitive joint-vetch 

(Aeschynomene virginica), barred owl (Strix varia), 

rare skipper (Problema bulenta), Rafinesque’s bigeared bat (Corynorhinus rafinesquii macrotis), Mabee’s 

salamander (Ambystoma mabeei), and the bald eagle 

(Haliaeetus leucocephalus). 

Marshes and other wetlands form where the land 

surface and geologic substrate combine to maintain 

a water-saturated environment. Clay-rich layers 

either deposited or left as residual clays where other 

(carbonate) minerals dissolved away act as impermeable 

layers. The presence of these layers near the surface 

together with the park’s gentle topography and 

proximity to sea level yields abundant marsh and tidal 

wetland habitat. Tidal marshes are considered globally 

rare (see “Soils” section). Monitoring in 2013 revealed 

the presence of 66 species of marsh birds, including 

rails and bitterns that are obligates of the tidal marsh 

and sensitive to changes within their breeding and 

foraging habitat; such habitat changes could occur due 

to relative sea-level rise (see “Sea Level Rise, Flooding, 

and Coastal Vulnerability” section) (Northeast Coastal 

and Barrier Network 2014).

13

Geologic Features and Processes

This chapter describes noteworthy geologic features and processes in Colonial National Historical 

Park.

During the 2005 scoping meeting (see ThornberryEhrlich 2005) and 2014 conference call, participants 

(see Appendix A) identified the following geologic 

features and processes:

● Fluvial Features and Processes

● Coastal Plain Sediments

● Slope Features and Processes

● Paleontological Resources

● Karst Topography and Cornwallis “Cave”

● Subsurface Geologic Features and the Chesapeake 

Bay Impact Crater

● Hydrogeologic System at Yorktown Battlefield

Fluvial Features and Processes

Meandering river channels, point bars, natural levees, 

and backswamp deposits are the primary fluvial features 

within and near the park. Fluvial processes in the 

park both construct (deposit) and erode landforms. 

The tidal James and York rivers and their tributaries 

(e.g., Powhatan Creek) acting on unconsolidated 

coastal plain sediments control sedimentation and 

geomorphology and hence the development of 

virtually all landforms in the James-York peninsula. 

Groundwater flow and more than 99 cm (39 in) of 

average annual precipitation supply the water for 

this river system (Speiran and Hughes 2001; Vanasse 

Hangen Brustlin, Inc. 2009). River currents can reach 

1 m/sec (3 ft/sec), but are generally lower and therefore 

dominate sediment resuspension and transport 

processes in the lower depths of the water column only 

(see “Bottom Sediments” section) (Friedrichs 2009; 

Dallas et al. 2013). Erosion and river meandering, along 

with waves, contribute to a major resource management 

issue: protecting shorelines with coastal engineering 

(see “Shoreline Erosion, Sediment Transport, and 

Coastal Engineering Structures” section). 

A classic meandering river channel consists of a series 

of fairly uniform S-shaped curves. The curves form 

because abundant sediment near an active channel 

accumulates in the meander belt into an alluvial ridge 

that has a higher elevation than the adjacent floodplain 

(Saucier 1994). The ridge then diverts the river’s flow 

laterally, causing the channel to broaden, shallow, 

and meander. As a river flows around curves, the flow 

velocity (and thus erosive energy) is greatest on the 

outside of the bend. The river erodes into its bank on 

the outside of a curve (cutbank) and leaves point bar 

deposits on the inside of the bend (fig. 9). As the process 

continues, the outside bend retreats farther from the 

channel, while the inside bend builds into the channel, 

thus creating migrating meanders. 

Point bars are crescent-shaped ridges of sand, silt, and 

clay deposited on the inside of meanders where the 

water’s velocity is slowest (fig. 9; Waterways Experiment 

Station 1951). A point bar’s shape conforms to the 

curvature of the channel, but bars may truncate each 

other forming a complex pattern as meander migration 

continues (Waterways Experiment Station 1951). 

As a meander migrates, successive point bars build 

up laterally. The curved, sand- and silt-cored ridges 

are separated by low, clay- and silt-rich swales. The 

alternating ridges and swales define classic point–

bar accretionary topography (fig. 9) (Waterways 

Experiment Station 1951; Saucier 1994). 

During high flows or floods, a river deposits natural 

levees of sand and silt along its banks. These deposits 

are the coarse-grained component of a river’s 

suspended sediment load and often form the highest 

reaches of an alluvial region. Natural levees also create 

well-drained farmland. By elevating the land surface 

with coarse sediment, porosity is increased and water is 

able to percolate downward and support crops without 

being swampy. Regular flood incursions also bring 

valuable nutrients to floodplains and levees. For these 

reasons, they have been the most significant landforms 

in human-settlement patterns, influencing building 

locations, transportation routes, agriculture, and 

industry development (Saucier 1994). 

Backswamps are low-lying places that retain water 

during floods or high flow (fig. 9). They are separated 

from the river channel by natural levees (Waterways 

Experiment Station 1951). Low relief and dense 

vegetation characterize a backswamp. The slack 
14

Figure 9. Illustration of fluvial processes of meandering. River meandering causes the formation of abandoned 

channels that infill with fine-grained sediments. Among the characteristic landforms resulting from river meander 

is ridge-and-swale topography visible at Jamestown Island. Graphic by Trista Thornberry-Ehrlich (Colorado State 

University) with information from Allen (1964).
15

floodwaters deposit layers of (fine-grained) clays and 

organic material (Waterways Experiment Station 1951).

In addition to the two large rivers (York and James), 

water bodies within the park include Sandy Bay, the 

Thorofare, Pitch and Tar swale (swamp), Yorktown, 

Mill, Powhatan, Kingsmill, Passmore, Indian Field, 

Felgate’s, King’s, Queen’s, Halfway, College, Papermill, 

Wormley, Beaverdam, and Ballard creeks; Great 

and Baptist runs; and the Back River (Lookingbill et 

al. 2012). Not counting the York and James rivers’ 

shorelines, more than 39 km (24 mi) of perennial 

streams and 49 km (30 mi) of intermittent streams 

and drainages traverse the landscape within Colonial 

National Historical Park (National Park Service 2014a). 

The erosion and meandering of these streams through 

the unconsolidated coastal plain sediments shape and 

reshape the landscape across the James-York peninsula. 

Jamestown Island exhibits some classic features of a 

river-influenced landscape such as a stair-stepped, 

ridge-and-swale topography (fig. 10). The uplands 

(ridge) consist of Church Point and Confederate 

Ruins ridges at about 3 to 4 m (10 to 13 ft) above 

sea level. They feature low, arcuate ridges formed in 

the Lynnhaven Member of the Tabb Alloformation 

(geologic map unit Qtl), which decrease in elevation 

towards the east. As mentioned in the “Geologic 

Significance and Connections” chapter, settlers made 

use of this valuable upland by siting James Fort, 

Jamestowne, and farms there (Johnson 2007). The lower 

ridges south of Passmore Creek are formed in the clays, 

silts, and sands of the Poquoson Member of the Tabb 

Alloformation (Qtp). Between adjacent ridges are lowlying swales and swamp or marshes (e.g., Pitch and Tar 

swale, Passmore Creek marsh, and Back River marsh.

Coastal Processes

The James and York rivers experience typical fluvial 

processes, but are also affected by coastal processes, 

such as tides, wind, and waves, which create brackish 

conditions in both rivers (salinity between 18 and 30 ppt 

at Yorktown and up to 18 ppt at Jamestown; Center for 

Coastal Resources Management et al. 2008). The fluvial 

and coastal processes transport sediment and shape the 

park’s shorelines. Tides from the Atlantic Ocean cause 

Figure 10. Cross section of Jamestown Island. Ridge-and-swale topography is obvious at Jamestown Island, 

particularly at Church Point, Confederate Ruins ridge, and the Passmore Creek ridges and marsh. Vertical scale is 

greatly exaggerated. Decreasing ridge elevations to the east are not visible on this graphic due to its north to south 

orientation. Graphic by Trista Thornberry-Ehrlich (Colorado State University) after figure 17 in Johnson (2007).
16

water level fluctuations in the Chesapeake Bay of less 

than 1 m (3 ft) on average (Yorktown station 8637689; 

Thornberry-Ehrlich 2005; National Oceanographic 

and Atmospheric Administration 2014). The tides are 

semi-diurnal, consisting of two high tides and two low 

tides each day (Vanasse Hangen Brustlin, Inc. 2009). 

Wave energy varies depending on the fetch distance, 

wind regime, nearshore bathymetry, and the orientation 

of the shoreline (Dallas et al. 2013). Fetch lengths in the 

southern Chesapeake Bay are generally less than

8 km (5 mi) and limits the local wave climate (Dallas et 

al. 2013). Wind patterns shift seasonally from the north 

and northwest during late fall to southwest in spring 

(Hardaway and Byrne 1999; Hardaway et al. 2006; 

Dallas et al. 2013). 

The most sediment transport and shoreline change 

occurs during major storms such as nor’easters, 

tropical storms, or hurricanes (e.g., Hurricane Isabel in 

2003) (Dallas et al. 2013). The effects of major storms 

are described in the “Shoreline Erosion, Sediment 

Transport, and Coastal Engineering Structures” section. 

Bottom Sediments

Mapping riverine bottom sediments is useful for 

defining faunal habitat and potential subaqueous 

sand and gravel resources. Recent mapping in the 

James River, offshore of Jamestown Island, revealed 

the presence of black, organic-rich muds in the 

central channel. Mapping also identified subaqueous 

sand which appears to migrate upstream in waves, 

transported by river currents; the sand fills in the 

dredged Goose Hill channel (see Goose Hill on

fig. 7; Berquist 2012). The GRI GIS data include several 

submerged mud and sand units (geologic map units 

Qsnd, Qom, Qsg, and Qshom), visible on the geologic 

map poster (in pocket) (Berquist 2010; Berquist 2015).

Coastal Plain Sediments

Loosely consolidated to unconsolidated sedimentary 

units underlie Colonial National Historical Park and 

represent the three main types of sedimentary rocks: 

clastic, chemical, and organic. Clastic sedimentary rocks 

are the products of weathering, erosion, transportation, 

and deposition of rock fragments called “clasts.” Clastic 

sedimentary rocks are named after the size of clasts (see 

table 1 for park examples). High-energy depositional 

environments, such as fast-moving streams, deposit 

larger (heavier) clasts while transporting smaller 

(lighter) clasts. Where water moves slowly or is 

stagnant, such as in lakes, the water cannot transport 

even the smallest clasts and they are deposited. Wind 

also transports and deposits sand-sized or smaller 

clasts (table 1). Chemical sedimentary rocks form 

through precipitation; an example is carbonate rocks 

such as limestone (calcium) or dolomite (calcium and 

magnesium). Organic sedimentary rocks are composed 

of organic remains (e.g., coal) or were produced by the 

physiological activities of an organism (e.g., secretion 

of calcium carbonate to form coral reefs). Sedimentary 

rock types record the environment of their deposition 

and those environments can shift laterally as conditions 

change; in doing so, laterally related depositional 

environments can become superimposed. This situation 

results in time-transgressive sedimentary formations 

where the vertical and lateral sequences of sedimentary 

facies are the same (fig. 11). In other words, sedimentary 

facies that occur in conformable vertical successions of 

strata also occur in laterally adjacent environments.

The geologic formations mapped along riverbanks and 

excavations on the lower James-York Peninsula range in 

age from the late Miocene (about 11 million years ago) 

to the present surficial deposits (see “Surficial Deposits” 

section). The units are broadly divisible into two types 

Table 1. Clastic sedimentary rock classification and characteristics.

Rock Name Local Example Clast Size Depositional Depositional 

Energy Setting

Conglomerate 

(rounded clasts) or 

Breccia (angular 

Pebble layers in Bacons Castle Formation (Qbc) 

and Shirley Alloformation (Qsh) >2 mm (0.08 in) [larger] Higher Energy Fluvial

clasts)

Sandstone Windsor Formation (Qw) 1/16–2 mm (0.0025–0.08 in) Fluvial

Siltstone Tabb Alloformation, Lynnhaven Member (Qtl) 1/256–1/16 mm (0.00015–

0.0025 in) Estuarine

Claystone Clay layers in the Tabb Alloformation (Qt, Qtp, 

Qtl, Qtlp and Qts)

<1/256 mm (0.00015 in) 

[smaller] Lower Energy Estuarine
17

(table 2): (1) older, relatively thin, fossiliferous, marine 

sediments with layers of relatively uniform thickness 

(flat) near their base, and (2) younger, fluvial-estuarine 

units with highly variable composition, thickness, and 

fossil content with undulating layers near their bases 

due to the in-filling of ancient valleys and shallower 

surfaces between valleys (“interfluves”) (Johnson 

2007). The younger fluvial-estuarine formations were 

deposited on a dissected terrain during global sea 

level rises and falls (transgressions and regressions) 

(Johnson 2007). The units are all described in detail 

in the Map Unit Properties Table. The history and 

spatial distribution of all these units are complex and 

still the subject of much study and debate among 

geologists. Areas of study include the lateral and vertical 

relationships among units and the number, distribution, 

and origin of formations that underlie the terraces 

on the coastal plain of Virginia (Johnson 2007). More 

investigation is needed to determine the nature of these 

units.

Table 2. Geologic formation types.

Type 1—mostly marine Type 2—mostly fluvial or 

estuarine

Yorktown Formation

(Tymh and Tc)

Tabb Alloformation

(Qt, Qtp, Qtl, Qtlp and Qts)

Eastover Formation (Tc) Shirley Alloformation (Qsh)

Chuckatuck Alloformation 

(Qc)

Charles City Alloformation 

(Qcc)

Windsor Formation (Qw)

Bacons Castle Formation 

(Qbc)

Figure 11. Illustration of the deposition of the Yorktown Formation (geologic map units Tymh and Tc). Because 

sedimentary environments vary spatially, sediments of different type are deposited at the same time within the same 

unit. Graphic by Trista Thornberry-Ehrlich (Colorado State University) with information from Berquist (2010).
18

Rock Exposures, Stratigraphic Sections, and Type 

Localities

Exposures of sedimentary rocks within and near the 

park have been studied for well over 150 years, although 

many of the historic exposures are now obscured or 

destroyed by coastal engineering structures (fig. 12). 

Historic accounts of the fossil beds in the Yorktown 

Formation (geologic map units Tymh and Tc) of the 

steep banks along the York River after the American 

Revolutionary War attest to their prominence and 

visibility (see “Geologic Significance and Connections” 

chapter). The excellent exposures of the local Yorktown 

Formation also make them ideal targets for field-based 

research experiences in local schools, community 

colleges, and universities. Exposures along the James 

River recently provided the material and setting to 

study sedimentology, stratigraphy, paleoecology, and 

taphonomy (the study of the environmental conditions 

affecting the preservation of animal or plant remains) 

at Thomas Nelson Community College (Layou et 

al. 2010). Such outcrops could provide important 

interpretive locations.

Geologists use exposures to describe geologic units 

and sequences to create a “section.” Sections used to 

officially designate a new geologic unit are called type 

sections. A type locality is the location of a type section 

where layers of rock (strata) were originally described. 

A type section is the standard for which exposures of 

the same strata in other locations may be compared. 

At least one type locality (Moore House Member of 

Yorktown Formation) is within the park as described 

below.

Type sections are typically selected for layers of 

sedimentary rocks that share similar characteristics, 

such as rock type (e.g., sandstone, shale, and siltstone), 

color, or distinctive features. Such a rock group is called 

a “formation.” An “alloformation” a kind of formation, 

in which the unit is defined and identified on the basis 

of its discontinuities that surround it rather than a 

particular composition (Prothero and Schwab 2004). 

Alloformations are commonly used to distinguish 

between superposed deposits (e.g, a succession of 

similar river and lake deposits, separated by soil layers), 

contiguous discontinuity-bounded deposits (e.g., 

overlapping lobes of slope deposits from different coldclimate periods), and geographically separated bodies 

(e.g., river terrace deposits), all of similar composition 

(Rawson et al. 2002).

Geologists usually name formations to reflect a 

geographic feature such as a river, mountain, or city 

(e.g., Yorktown Formation) where the layers are best 

seen. Formations can be lumped together into “groups” 

such as the Chesapeake Group or subdivided into 

“members” such as the Poquoson Member of the Tabb 

Formation. Type localities are searchable at the US 

Geological Survey’s online database:

http://ngmdb.usgs.gov/Geolex/search.

Yorktown, Virginia lends its name to the Yorktown 

Formation (Tymh and Tc), but there is no formal type 

locality and today, riprap covers most historic outcrops 

of the Yorktown Formation at Yorktown. The Yorktown 

Formation was divided into four members by Ward 

and Blackwelder (1980), in ascending order: Sunken 

Meadow, Rushmere, Morgarts Beach, and Moore 

House members. The Sunken Meadow member is 

considered the lower Yorktown Formation, whereas 

the latter three members compose the upper Yorktown 

Formation (Johnson 2007; Tweet et al. 2014). 

The Moore House Member, at the top of the formation, 

Figure 12. Photograph of cliff of Yorktown Formation 

ca. 1912. Exposures such as this were common along 

the York River in the vicinity of Yorktown prior to the 

installation of riprap and other shoreline engineering 

along much of the York River shore. Note person for 

scale. Photograph is from Clark et al. (1912) presented 

as COLO Figure 1 by Tweet et al. (2014). 
19

was named for Moore House in Colonial National 

Historical Park. Exposures in the park provided the 

type locality and include westward dipping sandy 

shell beds and cross-bedded shell hash (see “Karst 

Topography and Cornwallis Cave” section). At the top 

of the member in the Williamsburg vicinity, brackish 

water mollusks signaled the sea level regression and 

freshwater input at the end of the Yorktown Formation 

deposition (Ward and Blackwelder 1980). 

Slope Features and Processes

Slope movements are the downslope transfer of soil, 

regolith, and/or rock under the influence of gravity. 

Soil creep, rockfalls, debris flows, and avalanches are 

common types of slope movements. These processes 

and the resultant deposits are also known as “mass 

wasting” and commonly grouped as “landslides.” Slope 

movements occur on time scales ranging from seconds 

to years. Refer to figure 13 for illustrations of slope 

movements. Slope movements create geologic hazards 

and associated risks in many parks. Hazards and risks 

associated with slope movements in Colonial National 

Historical Park are described in the “Geologic Resource 

Management Issues” chapter. 

Slope movements are a natural geologic process and 

occur as small scale slumps and slope creep (fig. 14) 

on steep bluffs and ravines within Colonial National 

Historical Park. Areas undercut by erosion—itself a 

major issue in the park—are also prone to failure (see 

“Slope Movement Hazards and Risks” for more case 

studies). 

Paleontological Resources

Paleontological resources (fossils) are any evidence 

of life preserved in a geologic context (Santucci et al. 

2009). All fossils are nonrenewable. Body fossils are 

any remains of the actual organism such as bones, 

teeth, shells, or leaves. Trace fossils are evidence of 

biological activity; examples include burrows, tracks, 

or coprolites (fossil dung). Fossils in NPS areas 

occur in rocks or unconsolidated deposits, museum 

collections, and cultural contexts such as building 

stones or archeological resources. The NPS Fossils and 

Paleontology website,

https://www.nps.gov/subjects/fossils/index.htm, 

provides more information. As of February 2016, 261 

parks, including Colonial National Historical Park, had 

documented paleontological resources in at least one of 

these contexts. The park contains examples of all three. 

Tweet et al. (2014) prepared a paleontological resource 

summary report that details the documented and 

potential fossil resources for Colonial National 

Historical Park and other parks within the Northeast 

Coastal and Barrier Inventory and Monitoring 

Network. Significant fossil specimens have been 

found within park boundaries. These fossils present 

opportunities for education, interpretation, and 

scientific research. Notable fossil localities within the 

Yorktown Formation (geologic map units Tymh and Tc) 

are described in Tweet et al. (2014). The exact locations 

are considered sensitive information. Refer to the 

“Paleontological Resource Inventory, Monitoring, and 

Protection” section for resource management issues 

associated with fossils in the park.

Local fossils are historically significant to 

paleontological history. Many species were discovered, 

described, and named from locations in the park. 

In some areas, fossils are quite abundant (see inside 

cover). As described in the “Geologic Significance 

and Connections” chapter, the bivalve (mollusk) 

Chesapecten jeffersonius was likely the first fossil to be 

described in North America. It was included in Martin 

Lister’s Historiae Conchyliorum in the late 1600s, 

although at the time, it was not recognized as a fossil. 

Ward and Blackwelder (1975) described the story of the 

fossil that would later become the state fossil of Virginia.

Tweet et al. (2014) provided detailed tables of fossils 

named from specimens found or possibly found within 

Colonial National Historical Park—in summary: 

● 65 species of bivalves

● 33 species of gastropods

● 11 species of foraminifera

● 7 species of ostracods

● 2 species of barnacles

● 1 scaphopod mollusk

● 1 serpulid worm

● walrus

Other geologic map units occurring in Colonial 

National Historical Park have the potential to contain 

fossil resources. Notable among these is the potential 

for large, extinct Pleistocene mammal remains such as 

mammoths, mastodons, horses, and bison (Tweet et 

al. 2014). These are described in detail in Tweet et al. 

(2014) and on the Map Unit Properties Table.
20

Figure 13. Illustrations of slope movements. Different categories of slope movement are defined by material type, 

nature of the movement, rate of movement, and moisture content. Grayed boxes refer to settings that are not known 

to exist at Colonial National Historical Park. Graphic by Trista Thornberry-Ehrlich (Colorado State University) redrafted 

after a graphic and information in Varnes (1978).
21

Fossil discoveries in the vicinity of Colonial National 

Historical Park continue. In 2013, a partial skeleton 

of a baleen whale—nicknamed “Cornwallis”—was 

recovered from the Eastover Formation (Tc) along the 

York River outside of the park (McClain 2014; Tweet et 

al. 2014).

Fossils from the park and/or surrounding area are 

curated in at least a dozen museums in the United States 

and Europe as summarized by Tweet et al. (2014).

Using Yorktown Formation Fossil Resources to 

Determine Past Climates and Ecosystems

Paleoecology, or the study of past interactions among 

organisms and their environment, seeks to determine 

(1) how the organisms interacted with the environment 

and each other, as well as how those interactions 

changed over time, and (2) what environmental factors 

controlled the abundances and distributions of the 

fossil species. Winkelstern et al. (2013) used fossil 

bivalves (Mercenaria spp.) from the Rushmere Member 

of the Yorktown Formation (geologic map unit Tc) to 

estimate sea surface temperature and climate at seasonal 

resolution during the Pliocene Epoch (5.3 million 

to 2.6 million years ago) on the mid-Atlantic Coastal 

Plain. Oxygen isotope ratios of the seasonal growth 

layers within the shells revealed the coldest winter 

temperatures recorded in the Yorktown Formation 

averaged 17±2°C (63±3°F) and the warmest 

summer temperatures averaged 25±2°C 

(77±3°F). This was part of the mid-Pliocene 

warm period (3.3 million to 3.0 million years 

ago)—among the most critical geologic 

intervals for studying a relatively warm 

with high concentrations of atmospheric 

CO2

, with increased Gulf Stream heat flow 

coupled with reduced cool-water input. This 

information in turn helps to understand the 

potential effects of modern global climate 

change. 

The Yorktown Formation provided a 

case study for testing the methods of 

paleoecological investigation as to how the 

environment controlled the fossil assemblage. 

Samples were taken from King’s Mill, Virginia 

among other nearby sites. The analysis 

showed that species richness increased on 

muddy and sandy substrates with low stress 

(i.e., low wave energy, relatively constant 

temperature, or moderate salinity) conditions 

(Bush and Daley 2008). 

Karst Topography and Cornwallis “Cave”

Karst is a landscape that forms through the dissolution 

of soluble rock, most commonly carbonates such as 

limestone or dolomite (Toomey 2009). Caves, sinkholes, 

“losing streams,” springs, and internal drainage are 

characteristic features of karst landscapes. Caves 

are naturally occurring underground voids such as 

solutional caves (commonly associated with karst), lava 

tubes, sea caves, talus caves (a void among collapsed 

boulders), regolith caves (formed by soil piping), 

and glacier caves (ice-walled caves) (Toomey 2009). 

As of December 2015, cave or karst resources are 

documented in at least 159 parks, including Colonial 

National Historical Park. The NPS Caves and Karst 

website, https://www.nps.gov/subjects/caves/index.

htm, provides more information. According to Land et 

al. (2013), eight percent of the land area within Colonial 

National Historical Park is karst. The only documented 

“cave” in the park is Cornwallis cave—discussed 

below—which is not a natural feature.

Sinkholes or “closed depressions” are common features 

of the lower Coastal Plain. Locally, sinkholes occur 

on the terrace treads, underlain by carbonate-rich 

sediments from the Norge Upland, southeastward 

Figure 14. Illustration of slope creep. Creep is a very slow, more or 

less continuous downslope movement of material. Curved trees on 

park slopes are evidence of slope creep. Graphic by Trista ThornberryEhrlich (Colorado State University).
22

to the Todds flat (see fig. 3). The deepest sinkholes 

and greatest concentration of karst features in the 

Colonial National Historical Park region occur on the 

Grafton and Huntington flats. These can resemble 

anthropogenic earthworks and other battlefield-related 

depressions. 

The soluble carbonate rock in the park vicinity is most 

often fossiliferous layers of the Yorktown Formation, 

particularly the shell “hash” layers such as those that 

host Cornwallis cave (fig. 15; geologic map units Tymh

and Tc). As those layers dissolve, overlying insoluble 

material, such as the clay-rich Windsor Formation (Qw) 

collapse or subside into the voids (Johnson et al. 1993; 

Thornberry-Ehrlich 2005; Johnson 2007; Berquist 

2010). The thickness of these clay layers, which can vary 

extensively particularly where faults are present (see 

“Subsurface Geologic Features and the Chesapeake Bay 

Impact Structure” section), exerts substantial control 

over which karst features (e.g., sinkholes and springs) 

form there (Rick Berquist, Virginia Division of Geology 

and Mineral Resources, geologist, conference call, 

12 November 2014). For example, west of a fault that 

crosses the southern part of the Yorktown unit (see 

“Subsurface Geologic Features and the Chesapeake 

Bay Impact Crater” section), the hash layer is 3 m (10 ft) 

thick; east of the fault on the uplifted side, the hash is 21 

m (70 ft) thick and susceptible to extensive dissolution 

and the creation of subterranean voids; places like this 

are beneath the larger sinkholes at Yorktown Battlefield 

(Rick Berquist, conference call, 12 November 2014; 

Berquist 2015). 

The park’s subsidence sinkholes range in size from a 

few meters to more than 40 m (130 ft) in diameter and 

the deeper depressions can hold water for several weeks 

following a heavy rainfall. The size of the sinkhole varies 

with the elevation of the terrace (flat), thickness of the 

underlying carbonate layer, and proximity to adjacent 

streams, which may breach the sinkhole at any stage 

of development (Johnson et al. 1993). Deep sinkholes 

occur along Main Street in Yorktown, near the York 

River where the groundwater gradient is steepest. Karst 

ponds (or perennially wet sinkholes) include Grafton 

Pond complex and Brackens Pond (Thornberry-Ehrlich 

2005). 

The sinkholes tend to form in stages (fig. 16). Isolated, 

Figure 15. Map of the Yorktown Formation within park boundaries. The carbonate layers within the Yorktown 

Formation (geologic map units Tymh and Tc) are soluble and prone to karst-feature development including sinkholes 

and springs. Sinkhole formation is pronounced in the Yorktown Battlefield unit. Pink lines are park boundaries. 

Graphic by Jason Kenworthy (NPS Geologic Resources Division) using GRI GIS data and ESRI Light Gray Canvas 

basemap, (accessed 12 May 2016). 
23

shallow basins, less than 1 m (3 ft) deep characterize the 

early stage. With time, the basins deepen, become more 

extensive (≤2 ha [5 ac]), coalesce laterally, accumulate 

sediment (more than 4 m [13 ft]) from sheetwash 

and wind-blown input, and flood for periods of time 

(Johnson et al. 1993). During the last phase of sinkhole 

development, the basins are nearly filled with sediment 

reducing the landscape’s relief (Johnson et al. 1993).

Larger sinkholes have larger catchment areas and may 

become “self-perpetuating” as they become larger; 

they hold more water which increases dissolution, 

enlarging the sinkhole. (Johnson 2007). As the 

carbonate dissolves, a clay-residue layer is left behind 

and restricting groundwater flow across its surface. As 

the groundwater pools atop a clay-rich layer (called 

an “aquitard”), the dissolution and basin development 

progresses laterally, widening the sinkhole depression. 

Sinkhole development hampers development of 

surficial streams by reducing overland flow and 

erosion across the terrace surface (Johnson 2007). 

For more than 10,000 years, sinkholes of the JamesYork peninsula have been accumulating upwards 

of 4.5 m (14.8 ft) of organic material (an important 

paleoecological record), aeolian (wind-blown) detritus, 

and colluvium (Johnson 2007). 

As described in the “Geologic Significance and 

Connections” chapter, Cornwallis cave at Colonial 

National Historical Park is not a natural cave, but 

instead a two-chambered quarry into cross-bedded 

coquina (“shell hash”) beds of the Yorktown Formation 

(Tymh and Tc). In fact it is documented as an abandoned 

mineral land (AML) feature as described in that section 

of this report. The “cave” consists of two rooms; the 

larger is approximately 6.8 m by 3.4 m (22.3 ft by 11.2 

ft). The weakly cemented Yorktown Formation coquina 

erodes and dissolves easily; at least 4.5 metric tons

(5 tons) have crumbled from the cave since the 1790s 

(Santucci et al. 2001; Johnson 2007; Tweet et al. 2014). 

In addition to concerns about the feature’s stability, 

fossils exist within the cave (see “Geologic Resource 

Management Issues” chapter).

Subsurface Geologic Features and the 

Chesapeake Bay Impact Crater

The typical depiction of the Coastal Plain sediments as a 

thick, undeformed, seaward-dipping wedge of sediment 

is not entirely accurate. A variety of faults, deformed 

sedimentary layers, and regional unconformities occur 

Figure 16. Illustration of dissolution sinkhole formation. 

Dissolution sinkholes form from dissolution and 

downward to lateral erosion of unconsolidated 

material into the underlying cavities. Graphic by Trista 

L. Thornberry-Ehrlich (Colorado State University) after 

figures by Tihansky (1999, p.126–127). 
24

between sediment layers underlying Colonial National 

Historical Park and throughout the James-York 

Peninsula (Poag et al. 1991; Poag 1997; Johnson 2007). 

A fault is a fracture in rock along which rocks have 

moved. The three primary types of faults are normal 

faults, reverse faults, and strike-slip faults (fig. 17). Faults 

are classified based on the relative motion of rocks 

on either side of the fault plane as described in fig. 17. 

Discovery of the Chesapeake Bay impact crater in the 

1990s helped to explain the presence of many of these 

subsurface structures, as well as the location of river 

valleys and the Chesapeake Bay.

The Chesapeake Bay impact structure is not visible 

at the surface, as it is buried by thick sediments that 

accumulated over 35 million years. The feature consists 

of a central crater and circular basin (“annular trough”) 

surrounded by an outer fracture zone (fig. 18) (Johnson 

et al. 1998; Powars and Bruce 1999). Colonial National 

Historical Park straddles part of the annular trough 

and outer fracture zone. About 35 million years ago, a 

3-km (2-mi) -wide bolide (meteor or comet) slammed 

into a shallow sea near present-day Cape Charles on 

the Eastern Shore of Virginia (Powars and Bruce 1999; 

Johnson et al. 2001a). According to Johnson (2007) 

and Johnson et al. (2001a), the impact vaporized, 

melted, and ejected the bedrock from the central crater, 

affecting “basement” rock to a depth of more than 1,800 

m (6,000 ft). The impact shockwave fractured rocks and 

created numerous faults (see fig. 17 for schematic fault 

types) which down-dropped large and small blocks of 

rocks. The impact and subsequent rebound of Earth’s 

crust produced a central peak and giant blocks of 

rock were dislodged within or tumbled into the crater 

forming a chaotic accumulation of material referred to 

as a “megabreccia”.

The crater created an enormous depression that 

accumulated sediment for millions of years. Even 

after the crater was completely buried by sediments, 

subsidence and structural adjustments controlled postimpact depositional settings and stratigraphic relations 

within and among the younger geologic formations. 

Subsidence rates are higher in and adjacent to the 

crater. Units deposited across the disruption thicken 

into the ring-like depression (annular trough) adjacent 

to the crater itself (Powars and Bruce 1999). The 

massive weight of post-impact sediments in and around 

the impact structure reactivated some of the numerous 

faults. This created earthquakes. Seismic activity 

continues today, but the frequency and magnitude of 

these earthquakes have diminished (Johnson et al. 1998; 

Johnson 2007). These underlying geologic structures 

likely contributed to or controlled the development of 

the James and York rivers’ locations; the parallelism 

of the step-wise scarps of the James-York peninsula 

suggests the strong influence of episodic differential 

movement along the buried, impact-related structures 

(see “Shoreline Erosion, Sediment Transport, and 

Coastal Engineering Structures” section) (Powars and 

Bruce 1999; Thornberry-Ehrlich 2005). The impact 

structure may also have affected the distribution and 

Figure 17. Illustration of fault types. Movement occurs along a fault plane. Footwalls are below the fault plane and 

hanging walls are above. In a normal fault, crustal extension (pulling apart) moves the hanging wall down relative 

to the footwall. In a reverse fault, crustal compression moves the hanging wall up relative to the footwall. A thrust 

fault is similar to a reverse fault, but has a dip angle of less than 45°. In a strike-slip fault, the relative direction of 

movement of the opposing plate is lateral. Graphic by Trista Thornberry-Ehrlich (Colorado State University).
25

Figure 18. Map and cross section of the Chesapeake Bay impact structure. Colonial National Historical Park (pink 

outline) is within the outer fracture zone and part of the annular trough—a ring-shaped depression surrounding 

the peak ring of the central crater. The megablocks are fault-bounded packages of sedimentary units that slumped 

into the crater, juxtaposing units of different ages along angular unconformities. Graphic is adapted from Johnson 

(2007, figures 6 and 7) by Trista L. Thornberry-Ehrlich (Colorado State University) using ESRI World Imagery basemap, 

(accessed 8 October 2014).
26

quality of groundwater because it created marked 

boundaries in the subsurface, and movement along 

impact-related structures juxtaposed different units 

(Powars and Bruce 1999; Johnson 2007). A better 

understanding of the geometry and coastal plain 

stratigraphy is necessary and study is ongoing (Johnson 

et al. 2001a; Rick Berquist, Virginia Division of Geology 

and Mineral Resources, geologist, conference call, 12 

November 2014). 

Results from drilling, coring, and mapping efforts near 

Newport News suggest the presence of at least three 

north–south oriented faults, one of which crosses the 

park and the York River just east of Yorktown. The 

other two are south and east of Yorktown and have 

a down-to-the-west direction of movement. These 

are mapped on the GRI GIS source map (Berquist 

2015). These features are likely associated with the 

Chesapeake Bay impact structure and could potentially 

be reactivated, particularly if a large earthquake occurs 

elsewhere (see “Geologic Hazards and Risks” section) 

(Rick Berquist, conference call, 12 November 2014). 

Any movement along these faults may impact the park’s 

hydrogeologic system, karst features, and infrastructure, 

including the dams at Jones Mill Pond and Wormley 

Pond (Tim McLean, NPS Colonial National Historical 

Park, civil engineer, conference call, 12 November 

2014). Aside from earthquake generation, these faults 

influence the flow of groundwater, the location of 

karst topography, the thickness of sediments, and 

other geomorphology. More field work and drilling are 

necessary to accurately delineate the positions of these 

features (Rick Berquist, conference call, 12 November 

2014).

Recent mapping described by Gilmer and Berquist 

(2012) throughout the Coastal Plain of Virginia 

northwest of Colonial National Historical Park and east 

of Richmond has revealed the presence of regionally 

extensive faults. These down-to-the-east faults may 

indicate the presence of a now-buried basin that 

predates the Chesapeake Bay impact structure; this 

may correlate with other extensional basins along the 

east coast. Undeformed layers of the Bacons Castle 

Formation (geologic map unit Qbc) lie atop the faults, 

suggesting that significant movement predates its 

deposition. The faults were likely active during the 

deposition of the Yorktown Formation (Tymh and Tc). 

Faults and other shallow structures have the potential to 

affect groundwater flow dynamics (see “Hydrogeologic 

System at Yorktown Battlefield” section) in aquifers 

above the Cretaceous Potomac Formation—the oldest 

and most deeply buried Coastal Plain unit (Gilmer and 

Berquist 2012). 

Hydrogeologic System at Yorktown 

Battlefield

The groundwater system at Colonial National 

Historical Park impacted historic events and today it is a 

management concern due to threats on its water quality 

and quantity (see “Groundwater Quantity and Quality” 

section). Speiran and Hughes (2001) delineated the 

aquifers and confining units at Yorktown Battlefield 

to understand how groundwater was moving through 

the subsurface and supplying water to streams and 

wetlands. The battlefield is underlain by a system of 

relatively impermeable confining units (aquicludes) 

layered with permeable aquifers within the Yorktown, 

Bacons Castle, Windsor, Chuckatuck, Shirley, and 

Tabb formations and alloformations (geologic map 

units Tymh, Tc, Qbc, Qw, Qc, Qsh, and Qt), as well as 

Holocene surficial units (possibly Qal and Qms). See 

Map Unit Properties Table for more information. The 

deep part of the system is generally more than 45 m (150 

ft) below the surface and is poorly connected to the 

shallow part of the aquifer that nourishes the surface 

water features. The local shallow aquifer system consists 

of, with increasing depth, (1) the unconfined Columbia 

aquifer, (2) the Cornwallis Cave confining unit, (3) the 

Cornwallis Cave aquifer, (4) the Yorktown confining 

unit, and (5) the Yorktown-Eastover aquifer (fig. 19). 

The upper two units are laterally discontinuous because 

terrace deposits at different elevations are incised by 

stream valleys. The confining units are generally silty 

and clayey sediments that inhibit the flow of water. The 

aquifers consist of sandy and shelly sediments with 

abundant pore space for groundwater to permeate 

readily (Brockman et al. 1997; Speiran and Hughes 

2001).

The primary source of groundwater from the region’s 

shallow aquifer system is the Cornwallis Cave aquifer, 

the uppermost aquifer. It underlies nearly the entire 

Yorktown Battlefield except along Ballard Creek and 

the York River. The aquifer and surface water features 

are connected because streams have cut into the aquifer. 

Streams are not incised deeply enough to penetrate 

the deeper Yorktown-Eastover aquifer (Speiran and 

Hughes 2001).
27

Figure 19. Map of generalized groundwater flow through hydrogeologic units at Yorktown Battlefield. Red line on 

aerial image is the general trace of the cross section. Yellow lines indicate scarps (see figs. 3 and 4); pink line is park 

boundary. Orange and yellow unit colors correspond to units on the geologic time scale. Graphic is not to scale and is 

vertically exaggerated. Note the discontinuous nature of the perched Columbia aquifers and Cornwallis Cave confining 

units due to the presence of the step-wise riverine scarps and incision of Beaverdam Creek. The Yorktown-Eastover 

aquifer is completely buried throughout the battlefield area. Graphic is adapted from Speiran and Hughes (2001, 

figure 11) with information from Johnson (2007) by Trista L. Thornberry-Ehrlich (Colorado State University). 

29

Geologic Resource Management Issues

This chapter describes geologic features, processes, or human activities that may require management 

for visitor safety, protection of infrastructure, and preservation of natural and cultural resources in 

Colonial National Historical Park. The NPS Geologic Resources Division provides technical and policy 

assistance for these issues.

Unsurprisingly for a park that is located between two 

major rivers and about 48 km (30 mi) west of the mouth 

of the Chesapeake Bay, there are significant resource 

management issues associated with surface and 

ground water. During the 2005 scoping meeting (see 

Thornberry-Ehrlich 2005) and 2014 conference call, 

participants (see Appendix A) identified the following 

geologic resource management issues:

● Sea Level Rise, Flooding, and Coastal Vulnerability

● Shoreline Erosion, Sediment Transport, and Coastal 

Engineering Structures

● Stormwater Management along Colonial Parkway 

and Upland Erosion

● Paleontological Resource Inventory, Monitoring, 

and Protection

● Geologic Hazards and Risks

● Groundwater Quantity and Quality

● Karst Landscape Management

● Yorktown Formation Shrink-and-Swell Clays

● Abandoned Mineral and Disturbed Lands

Resource managers may find Geological Monitoring

(Young and Norby 2009; http://go.nps.gov/

geomonitoring) useful for addressing some of 

these geologic resource management issues. The 

manual provides guidance for monitoring vital 

signs—measurable parameters of the overall 

condition of natural resources. Each chapter covers 

a different geologic resource and includes detailed 

recommendations for resource managers and suggested 

methods of monitoring.

Lookingbill et al. (2012) provided a natural resource 

condition assessment that describes the natural features 

within the park in context of the geographic location, 

legislative mission, and history. 

The park’s most recent general management plan 

emphasized the need to manage the park’s natural 

resources consistent with the National Park Service’s 

philosophy on management of cultural zones (Colonial 

National Historical Park 1993). 

The park has fostered partnerships with outside 

agencies to conduct in-park research, including 

Virginia’s Water Quality Board, Department of Game 

and Inland Fisheries, Natural Heritage Program, and 

Department of Forestry; the US Geological Survey; 

the US Soil and Conservation Service; the US Fish 

and Wildlife Service; the Virginia Institute of Marine 

Science; the College of William and Mary; Hampton 

University; and the Virginia Division of Geology and 

Mineral Resources (VDGMR) (Rafkind 1990). These 

types of working relationships contribute greatly 

to knowledge of the natural resources, geologic 

foundation, and ecosystems within the park. 

Sea Level Rise, Flooding, and Coastal 

Vulnerability

Colonial National Historical Park spans a peninsula 

between two major rivers and is within several meters of 

sea level. In addition, the York and James rivers are both 

tidally influenced in the park region. Within the park, 

tidal fluctuations average about 1 m (3 ft) on average 

(Yorktown station 8637689; Thornberry-Ehrlich 

2005; National Oceanographic and Atmospheric 

Administration 2014). Therefore, park lands, as well 

as cultural and natural resources, are particularly 

vulnerable to changes in relative sea level and flooding 

associated with storms. Climate change models for 

Virginia and the rest of the southeast U.S. predict sea 

level rise, and an increase in the frequency, intensity, 

and duration of strong storms such as hurricanes 

(Melillo et al. 2014; Caffrey and Beavers 2015).

Caffrey and Beavers (2015), using data from the 

Intergovernmental Panel on Climate Change (IPCC 

2013), reported sea level rise of 4.6 mm (0.18 in) per 

year from 1927 to 2013 at the Sewells Point tide gauge. 

Sea level rise presents management issues. Sea level rise 

in the 19th century raised the water table and caused 

brackish water incursions into what was previously 

nearly fresh groundwater. This had a profound impact 
30

on Jamestown Island agriculture as marshes and 

swamps migrated up the swales on Jamestown Island 

and other low-lying places. The cultural resources at 

the western end of Jamestown Island are particularly 

vulnerable to degradation (from saturated soil) and loss 

from rising water (eroding away; Johnson 2007). Sea 

level at Jamestown Island has risen slightly less than 1 

m (3 ft) in the 400 years since European occupation 

(Johnson 2007).

Between 1950 and 2003, the mean sea level trend at the 

Gloucester Point gauge was an increase of 3.81 mm/

year (0.15 in/year), much larger than the 20th century 

global average of 1.7 mm/year (0.07 in/year) and 

probably due to local subsidence (Church and White 

2006; National Park Service 2011; Dallas et al. 2013).

This process continues today and is a major concern for 

groundwater quality (see “Groundwater Quantity and 

Quality” section). The death of pine trees on the low 

ridges south of Passmore Creek is evidence of increased 

groundwater salinity as sea level continues to rise and 

groundwater becomes increasingly brackish (Johnson 

2007). Local river salinity ranges from 18 to 30 ppt at 

Yorktown and up to 18 ppt at Jamestown (Center for 

Coastal Resources Management et al. 2008).

The park’s Natural Resource Condition Assessment 

(Lookingbill et al. 2012) also identified sea level rise 

and increased severity and frequency of storms as a 

regional threat to natural and cultural resources. Global 

sea level has risen approximately 20 cm (8 in) over 

the past century and the rate of change is expected to 

continue increase into the next century (Melillo et al. 

2014). A 1-m (3.3-ft) rise in sea level will inundate over 

80% of Jamestown Island (fig. 20) (Saunders et al. 2010; 

Dallas et al. 2013). Caffrey and Beavers (2015) used 

Intergovernmental Panel on Climate Change (IPCC) 

data to project additional sea level rise at Colonial 

National Historical Park between 27 and 28 cm (10.6 

and 11.0 in) by 2050 and between 64.0 and 81.4 cm 

(25.2 and 32.0 in) by 2100.

Flooding during storm events such as nor’easters and 

hurricanes is likely to increase in severity and frequency 

as climate continues to change, with projected storm 

intensity and rainfall rate increases (e.g., Melillo et al. 

2014; Caffrey and Beavers 2015). The annual wettest 

month and wettest quarter are now considered extreme 

relative to historic conditions (Monahan and Fisichelli 

2014). At present, places such as Pitch and Tar swale, 

Passmore Creek marsh, and large areas of Church 

Figure 20. Map of flood-vulnerable areas of Jamestown Island. Sea level rise of 1 m (3 ft) will inundate a vast majority 

of Jamestown Island. Graphic is figure 20 in Dallas et al. (2013) adapted from Saunders et al. (2010).
31

Point and Confederate Ruins ridges flood during major 

storms. As just one example of infrastructure loss 

during such a storm, a nor’easter destroyed the pier and 

docks of Yorktown’s waterfront in 1985 (Lookingbill et 

al. 2012).

The James River has long fetches on both the eastern 

and western ends of the island. In 2003, storm surges 

associated with Hurricane Isabel damaged shoreline 

stabilization structures, eroded beaches, washed away 

several archeological sites along the Parkway and on 

Jamestown Island, and severely damaged the Jamestown 

visitor center (damaging or destroying artifacts there) 

and several tour road bridges (Thornberry-Ehrlich 

2005; Johnson 2007; Lookingbill et al. 2012). In 

addition to flooding, storms concentrate erosive waves 

on the park’s shoreline, as detailed in the “Shoreline 

Erosion, Sediment Transport, and Coastal Engineering 

Structures” section.

Caffrey and Beavers (2015) presented potential storm 

surge heights and extents within Colonial National 

Historical Park for hurricanes of category 1 and 3 on the 

Saffir-Simpson scale. They also projected a storm surge 

height of 5.27 m (17.3 ft) above current mean sea level 

at the Historic Jamestowne Visitor Center for a category 

4 hurricane. The visitor center would likely remain 

dry during a category 1 hurricane; at least one such 

hurricane should be expected to reach the park by 2100 

(Caffrey and Beavers 2015). Another storm-inundation 

estimate also known as sea, lake and overland surges 

from hurricanes (SLOSH) was completed using LiDAR 

for the elevations; this differed from the previous 

estimate as much as 27% of the time for category 1 

hurricanes (Shaw and Bradley 2014; Amanda Babson, 

NPS Northeast Region, coastal climate adaptation 

coordinator, written communication, 26 March 

2015). The geospatial data for this study, including 

inundation estimates for various sea level scenarios, are 

available at: https://irma.nps.gov/DataStore/Reference/

Profile/2216861 (accessed 11 May 2016). 

The US Geological Survey has conducted coastal 

vulnerability index (CVI) assessments for a number 

of units in the National Park System, but not yet at 

Colonial National Historical Park. CVIs have been 

completed for Assateague Island National Seashore 

and Cape Hatteras National Seashore, 87 km (54 mi) 

to the north and 96 km (60 mi) to the south of Colonial 

National Historical Park, respectively (Pendleton et 

al. 2004, 2005). CVIs use tidal range, wave height, 

coastal slope, shoreline change, geomorphology, 

and historical rate of relative sea level rise to create a 

relative measure of the coastal system’s vulnerability 

to the effects of sea level rise. The approach takes into 

account a coastal system’s natural ability to adapt to 

changing environmental parameters. Coarse data for 

the southeast region, including Virginia, presented 

in Melillo et al. (2014) showed the Tidewater area of 

Virginia to have “very high” vulnerability to sea level 

rise.

A park-specific CVI would provide data for resource 

management and park facilities plans at Colonial 

National Historical Park. The park submitted a 

vulnerability assessment request and is tentatively 

scheduled to receive one in 2019; however, an earlier 

date would be preferable (GRI conference call 

participants, 12 November 2014). For more information 

about CVIs, refer to the US Geological Survey CVI 

website: http://woodshole.er.usgs.gov/project-pages/

nps-cvi/. 

According to Monahan and Fisichelli (2014), climate 

change will likely affect all aspects of park natural and 

cultural resource management. Caffrey and Beavers 

(2015) noted the following potential impacts due to sea 

level rise and storm surge vulnerability at the park:

● Increasing sea levels may lead to loss of land and 

critical habitat.

● Increased erosion and/or accretion across the 

coastline by storms coupled with shorelines 

adjusting to new mean sea levels.

● Rising groundwater tables and possible salt water 

intrusion due to rising sea levels.

● Increased risk of impacts related to high intensity 

storm events.

● Potential loss of nearby freshwater ecosystems due 

to saltwater intrusion into groundwater as sea level 

rises.

Park resource managers are very concerned about the 

vulnerability of cultural resources in locations that 

models predict will be submerged and potentially lost 

(Jonathan Connelly, NPS Colonial National Historical 

Park, cultural resources manager, conference call 12 

November 2014). Effective planning and management 

must incorporate an understanding of past dynamics, 

present conditions, and projected change (Monahan 
32

and Fisichelli 2014). NPS Policy Memorandum 14-02 

(Jarvis 2014) identifies specific foci for adaptive research 

and management activities related to cultural resources, 

and provides guidelines for decision-making to avoid 

impairment of these resources in the face of climate 

change. The forthcoming NPS Coastal Adaptation 

Strategies Handbook (Beavers et al., in prep), expected 

in summer 2016, summarizes NPS guidance and 

strategies for cultural resources adaptation. 

The summary report from the Preserving Coastal 

Heritage workshop (National Park Service 2014c) 

identified and described seven climate change 

adaptation options for cultural resources: no active 

intervention; offset stresses; improve resilience; manage 

change; relocate/facilitate movement; document and 

release; and interpret the change. Melnick et al. (2015) 

have expanded these options to apply them specifically 

to cultural landscapes. 

Lookingbill et al. (2012) recommended proactively 

managing, intervening, and closely monitoring sea level 

markers and groundwater salinity. The National Park 

Service Climate Change Response Program facilitates 

climate change adaptation planning. 

Melillo et al. (2014) focused on three types of options 

to adapt to rising sea level: (1) protect (e.g. building 

levees or installing riprap), (2) accommodate (e.g., 

raising structures or using wetland restoration), and (3) 

managed retreat (e.g. allowing areas to be exposed to 

flooding by removing coastal protection).

Stevens et al. (2010) proposed a climate change 

monitoring work plan for the ecosystems in Colonial 

National Historical Park as part of the Northeast 

Coastal and Barrier Network, excerpts of which are 

presented in table 3.

Table 3. Proposed climate effects monitoring plan.

Ecosystem

type Metric (indicator)

Status and/or 

recommendation

as of 2010

Beaches and bluffs

Shoreline position, beach and dune topography Currently monitored

Precipitation, snow depth and cover, surface soil moisture, relative humidity, wind speed, air 

temperature, wave characteristics, tidal range, water surface elevation, High priority recommendation

Shoreline structures, beach nourishment Medium priority 

recommended

Depth to water table, salinity of groundwater, nearshore topography, bathymetry, bottom 

configuration, movement of sand supply Future consideration

Estuarine

Water temperature, salinity, sediment parameters, turbidity Currently monitored

Precipitation, snow depth and cover, relative humidity, wind speed, air temperature, surface soil 

moisture, wave characteristics, tidal range, water surface elevation, High priority recommendation

Depth to water table, salinity of groundwater, benthic habitat mapping Future consideration

Tidal marsh

Water temperature, salinity, water depth, marsh sediment elevation, accretion, erosion, and 

shallow subsidence, tidal marsh pool creek, ditch size category and distribution, turbidity Currently monitored

Tidal marsh capital and sediment budget, tidal range, frequency of inundation, precipitation, 

snow depth and cover, relative humidity, wind speed, air temperature, surface soil moisture, 

wave characteristics, water surface elevation

High priority recommendation

Depth to water table, groundwater salinity, soil pore water salinity, tidal marsh soil temperature, 

bulk density, and organic matter, sediment processes Future consideration

Uplands and 

freshwater

Soil characteristics, stream flow, lake and pond levels, stream pH and temperature, changes in 

land cover type, stream geomorphology Currently monitored

Precipitation, snow depth and cover, relative humidity, wind speed, air temperature, surface soil 

moisture High priority recommendation

Depth to water table, groundwater salinity, freshwater wetland and vernal pool levels, 

temperatures, and extents Future consideration

Note: Biological and water quality indicators were omitted. Information is from Stevens et al. (2010)
33

In the Geological Monitoring chapter about coastal 

features and processes, Bush and Young (2009) 

described the following methods and vital signs for 

monitoring coastal features and processes:

(1) shoreline change, (2) coastal dune geomorphology, 

(3) coastal vegetation cover, (4) topography/elevation, 

(5) composition of beach material, (6) wetland position/

acreage, and (7) coastal wetland accretion.

NPS has multiple resources related to climate change 

adaptation. The forthcoming NPS Coastal Adaptation 

Strategies Handbook will include NPS policies relevant 

to climate change, guidance on evaluating appropriate 

adaptation actions, and adaptation opportunities for 

planning, incident response, cultural resources, natural 

resources, facilities and assets, and infrastructure. The 

handbook will also provide guidance on developing 

communication and education materials about climate 

change impacts, and it will detail case studies of the 

many ways that individual parks are implementing 

adaptation strategies for threatened resources.See also 

Appendix B. 

Additional Reference Manuals that guide coastal 

resource management include NPS Reference Manual 

#39-1: Ocean and Coastal Park Jurisdiction, which 

can provide insight for parks with boundaries that may 

shift with changing shorelines (available at http://www.

nps.gov/applications/npspolicy/DOrders.cfm); and 

NPS Reference Manual #39-2: Beach Nourishment 

Guidance (Dallas et al. 2012) for planning and managing 

nourishment projects.

The NPS Geologic Resources Division (GRD) and 

Climate Change Response Program (CCRP) are 

developing sea level rise and storm surge data that 

parks can use for planning purposes over multiple time 

horizons. The project, led by Maria Caffrey of GRD, 

should be completed by 2016 and will analyze rates of 

sea level coupled with potential storm surge in 105 of 

the vulnerable parks in order to project, for each park, 

the combined elevations of storms surge and sea level 

by 2030, 2050, and 2100. Gonzalez (2015) prepared 

a climate change summary for Colonial National 

Historical Park that serves as a quick reference guide 

to climate change trends and historical impacts for the 

region. 

The NPS has also developed a report entitled “Adapting 

to Climate Change in Coastal Parks: Estimating the 

Exposure of FMSS-Listed Park Assets to 1 m of SeaLevel Rise” (Peek et al. 2015). This report includes the 

geospatial location and approximate elevation of over 

10,000 assets in 40 coastal parks (not Colonial National 

Historical Park), based on information within the NPS 

Facilities Management Software System (FMSS) and 

supplemented with other datasets, collaboration with 

park staff, and field visits to locate assets. Assets were 

characterized based on their overall exposure to longterm (1 m [3 ft]) sea level rise and associated storm 

vulnerability, and were categorized as having either high 

exposure or limited exposure to sea level rise impacts. 

Shoreline Erosion, Sediment Transport, and 

Coastal Engineering Structures

In addition to inundation via flooding and sea level 

rise, there are significant resource management issues 

associated with shoreline erosion and sediment 

transport. Shoreline protection structures were installed 

in many reaches of the park in attempts to manage 

shoreline erosion. These coastal engineering structures 

reduce erosion in some places but also present resource 

management concerns. 

Shoreline Erosion

Shoreline erosion is a natural process of river systems 

at all scales and is particularly evident when rivers cross 

landscapes consisting primarily of unconsolidated 

sediments, such as the coastal plain of Virginia. This 

process is exacerbated by storms such as hurricanes 

or nor’easters. In 2003, Hurricane Isabel produced 

2-m (6-ft) -high waves every 5 seconds in the York 

River during a 12-hour storm surge that started from 

the north and swung south as the storm passed. This 

passing storm drove erosive waves in several different 

directions against the park’s shorelines and damaged 

or destroyed several archeological sites. In Yorktown 

along the commercial waterfront, some nearshore 

breakwaters and other shoreline stabilization structures 

were damaged and the beach was completely washed 

away. An erosional scarp, in places only 1 to 2 m (3 to 6 

ft) from the Colonial Parkway, formed along stretches of 

the York River (Thornberry-Ehrlich 2005).

National Park Service management policies (see 

Appendix B) typically allow natural processes to occur 

and only suggest intervention when there is no other 

feasible way to protect park resources or facilities. 

Because much of the historical significance and cultural 

resources in Colonial National Historical Park are 

associated with and located along the shoreline, erosion 
34

is a critical concern. Historic rates of shoreline change 

vary with location and amount of anthropogenic 

interference (i.e., shoreline nourishment and/or 

installation of shoreline protection structures). Between 

1937 and 2009 the shoreline change rate (negative 

values for overall shoreline loss) in the Jamestown unit 

ranged from -1.2 to 7.0 m/year (-4.0 to 23.1 ft/year), 

with an overall average rate of 0.1 m/year (0.4 ft/year) 

(Milligan et al. 2010; Dallas et al. 2013). Between 1937 

and 2002, rates of shoreline change for the York River 

varied between -1.3 to 0.5 m/year (-4.2 to 1.5 ft/year), 

with an overall average rate of -0.12 m/year (-0.39 ft/

year) (Hardaway et al. 2006; Dallas et al. 2013).

Within the park, shoreline loss is more pronounced 

along the James River than the York River

(fig. 21) (Lookingbill et al. 2012; GRI conference call 

participants, 12 November 2014). When European 

settlers arrived at Jamestown Island in 1607, the 

shoreline was more than 120 m (400 ft) to the west of 

its 2001 position (Johnson et al. 2001b). Since 1607, 

Jamestown Island was extensively eroded on almost 

all sides, except along Back River, by storm-generated 

high tides and strong waves and currents. It was long 

suspected that the site of the original Jamestowne 

settlement of 1607 had washed into the James River. 

However, archeological excavations at the behest of 

Preservation Virginia (http://www.preservationvirginia.

org) uncovered the postholes of the original James 

Fort beneath American Civil War era earthworks on 

Jamestown Island. Further research showed one end of 

the fort had only partially washed into the river (Kelso 

and Straube 2004). Between 1894 and 1901, a seawall 

was constructed along the western edge of Jamestown 

Island to curb erosion; this present structure is still 

functioning and is now considered historic (US Army 

Corps of Engineers 2002; Johnson 2007; Eshleman 

2009).

A Civil War era fort near College Creek was lost to 

erosion (GRI conference call participants, 12 November 

2014). An isthmus that connected the island to the 

mainland was breached in the 1700s, necessitating 

construction of a now subsiding road and causeway 

in the early 1900s (Thornberry-Ehrlich 2005). The 

park is undertaking a large-scale effort to document 

and preserve cultural resources along the shores of 

Jamestown Island before erosion impacts or destroys 

them (Jonathan Connelly, NPS Colonial National 

Historical Park, cultural resource manager, conference 

call, 12 November 2014). 

At an archeological site, slope wash and tidal 

undercutting are causing loss of material that is 

noticeable on a weekly scale. Trees are also washing into 

the channel’s strong currents. This creates a dangerous 

situation for swimmers because these underwater 

trees are not visible from above and they shift position 

within the channel (GRI conference call participants, 12 

November 2014).

The Yorktown unit and Colonial Parkway are located 

along the south bank of the York River, which is 

migrating southward. The southern shore of the river 

near Yorktown is eroding two to three times faster than 

the northern shore at Gloucester Point (ThornberryEhrlich 2005). Near kilometer five (mile three) of the 

Colonial Parkway, there is no protective riprap along 

the shoreline, and erosion is threatening the roadway. 

This and several other stretches of the parkway on both 

sides of the peninsula are at risk of being damaged (Tim 

McLean, NPS Colonial National Historical Park, civil 

engineer, conference call, 12 November 2014). 

Figure 21. Map of shoreline loss at Black Point. Between 

the years 1874 and 2007 more than 61 m (200 ft) of 

shoreline was eroded by the James River. Aerial image 

taken in March 2007. National Park Service photograph 

courtesy of Colonial National Historical Park presented as a 

figure in Lookingbill et al. (2012, p. 27). 
35

Erosion along the James River and York River shorelines 

within the park and along the Colonial Parkway 

ranges from 0 to 0.58 m (0 to 1.9 ft) per year (National 

Park Service 1999; Lookingbill et al. 2012). Shoreline 

erosion rates have been increasing over the past several 

thousand years as sea level has been rising throughout 

the Holocene, exposure to storms has increased, and 

the landscape relief has decreased (Johnson 2007). 

Sediment Transport and Dredging

Rivers are not only agents of erosion, they also transport 

and deposit tremendous amounts of sediment. In order 

to maintain channels for large ships travelling upstream 

to Richmond, the US Army Corps of Engineers (ACOE) 

dredges channels in both the York and James rivers. 

Disposing of this material in a suitable and safe manner 

has been a long-term goal of the US ACOE (Zappi et al. 

1990).

Dredge material from the “Hampton Roads” 

geographical area composes entire landforms such as 

Craney Island (also used for the disposal of dredge 

material for naval use), as well as Naval Channel, 

York River, Thimble Shoal, Wolf Trap, and Dam Neck 

disposal sites (Zappi et al. 1990). On the James River, 

dredging occurs about 30 to 60 m (100 to 200 ft) from 

the park boundary. Once the channel is dredged, the 

channel refills with sand moving between Hog Island 

and Jamestown Island. Side-scan imagery, used to map 

the bottom sediments presented in the GRI GIS data 

(e.g., geologic map units Qsnd, Qom, Qsg, and Qshom), 

identified significant shifting of bottom sediments.

It remains unclear if the net sand loss is coming from 

Jamestown Island or elsewhere (Rick Berquist, Virginia 

Division of Geology and Mineral Resources, geologist, 

conference call, 12 November 2014). By removing 

subaqueous sediment and changing river current 

patterns, dredging can exacerbate erosion along the 

Colonial Parkway between College and Middle creeks 

and threaten the stability of the road (Tim McLean, 

conference call, 12 November 2014). 

Coastal Engineering Structures

Efforts to stabilize the shorelines and protect resources 

at Colonial National Historical Park include installation 

of breakwaters, bulkheads, piers, revetments, groins, 

sea walls, sills, riprap, lines of rock, sand replenishment 

(“beach nourishment”), marsh plants (creating 

wetlands), shoreline measuring stakes (to determine 

quantitative measures of accretion or retreat), 

stonewalls, and planting vegetative interfaces (fig. 22) 

(Thornberry-Ehrlich 2005; Dallas et al. 2013). Some of 

these structures were installed more than 100 years ago 

(fig. 23) (Simon 2012).

A coastal engineering inventory was completed by 

Dallas et al. (2013) and includes GIS data. The US 

ACOE (2002) also prepared a detailed environmental 

assessment of the shorelines of Jamestown Island 

and the adjacent peninsula. Refer to those reports for 

detailed descriptions and management options. In 

summary:

● 153 coastal engineering projects occur within or 

immediately adjacent to the park. These projects 

include 134 coastal structures (55 in or near the 

Yorktown unit and 79 in or near the Jamestown 

unit), 11 fill projects, and eight beach nourishment 

projects.

● About 39% of the shoreline within the park is 

stabilized, with coastal structures extending for 

15,070 m (49,450 ft).

● Beach nourishment projects moved at least

30,000 m3 (39,000 yd3) of sediment between 1985 

and 2009.

● Fill projects impacted approximately 0.48 km2

(118 ac) of subaerial and submerged land within 

the park between 1931 and 1955 (Dallas et al. 

2013). Artificial fill is included in the GRI GIS 

data (Qf) (see Map Unit Properties Table for more 

information; Berquist 2010).

● Armored shoreline is 28% of the total at Jamestown 

(fig. 24) (Dallas et al. 2013).

● Riprap was installed along the benchmark at Black 

Point on Jamestown Island. Sand is currently 

accumulating there, but visitor use of the beach has 

prevented stabilizing vegetation from flourishing 

(Johnson 2007; Eshleman 2009).

● At Yorktown, riprap currently covers much of 

the bluffs and outcrops; 66% of the shoreline is 

armored (figs. 25 and 26) (Thornberry-Ehrlich 

2005; Dallas et al. 2013).

● Riprap was installed along reaches of the 

Colonial Parkway to prevent further erosion and 

compromising of the roadway.

These structures were designed to stabilize the shoreline 

in order to protect cultural resources, and have had 
36

Figure 22. Photographs of shoreline stabilization structures. Riprap and artificial fill (geologic map unit Qf) were 

installed on many shorelines within the park. In some places, vegetation is able to grow behind the riprap, in others, 

refracted waves cause erosion behind the structure. National Park Service photographs taken by Melanie Peters (NPS 

Geologic Resources Division) in August 2005.
37

Figure 23. Aerial image of the Jamestown seawall and the James River. The north direction is toward the top of the 

image. The southwest corner of the James Fort was lost to erosion prior to the construction of the 730-m (2,395-ft) 

concrete seawall. The ACOE-constructed seawall is deteriorated and in need of repair as it is considered historic and 

is still functioning to protect the fort. It reduces sediment supply to shoreline downstream and may have necessitated 

more armoring downstream. View is to the northeast. Graphic is figure 16 in Dallas et al. (2013); numbers refer to 

references in that report.

Figure 24. Map of coastal engineering structures along the shorelines in the Jamestown unit. The yellow shaded area 

is within Colonial National Historical Park boundaries. Graphic is figure 6 in Dallas et al. (2013); numbers refer to 

references in that report.
38

Figure 25. Map of coastal engineering structures along the shorelines in the Yorktown unit. The yellow shaded area is 

within Colonial National Historical Park boundaries. Yellow box indicates area enlarged in figure 26. Graphic is figure 9 

in Dallas et al. (2013); numbers refer to references in that report.

Figure 26. Enlarged map of coastal engineering structures along the shorelines in Yorktown. The yellow shaded area 

is within Colonial National Historical Park boundaries. Graphic is figure 12 in Dallas et al. (2013); numbers refer to 

references in that report.
39

mixed results in meeting their objective illustrating 

the challenges associated with resource managment in 

such an environment (Dallas et al. 2013). Breakwaters 

installed at Yorktown between 1994 and 2005, and 

at Jamestown Island in 2002, have been somewhat 

successful in preserving a scalloped shoreline of 

trapped-sediment salients (projections of sediment that 

jut outward from the coast) and/or tombolos between 

the breakwaters and the shore (fig. 22). Passmore Creek, 

however, bypassed a riprap structure meant to confine 

the channel and created a new channel to the James 

River which threatened cultural resources (ThornberryEhrlich 2005). All of these structures can be overtopped 

during storms. Hurricane Isabel in 2003 clearly 

illustrated the park’s vulnerability to inundation when 

storm surge breached revetments as high as 2 m

(6 ft) along the York River (Dallas et al. 2013).

The coastal engineering structures also likely altered 

the natural sediment transport processes in the region 

(Dallas et al. 2013). Armoring within and adjacent to 

the park has limited the sediment supply to the region’s 

beaches (Dallas et al. 2013). Given the overall erosive 

nature of the system, coupled with a lack of available 

sediment supply, unarmored regions are particularly 

vulnerable to wave action and erosion processes 

(Dallas et al. 2013). Shorelines are retreating from rock 

revetments put in place along reaches of the Colonial 

Parkway. It remains unclear at this time whether the 

revetments are exacerbating the situation and if they 

may need to be moved or removed completely (Tim 

McLean, conference call, 12 November 2014).

A Rutgers University research group used the Dallas 

et al. (2013) inventory to identify structures that could 

be removed for shoreline loss mitigation; results were 

expected in 2015 (Dorothy Geyer, NPS Colonial 

National Historical Park, natural resource specialist, 

conference call, 12 November 2014). Their preliminary 

report suggested removing breakwaters on the 

southeast end of Jamestown and restricting attempts to 

rebuild or improve protection structures along other 

selected sites in order to allow natural marshes and 

beaches to form and keep pace with relative sea level 

rise. The chosen study sites are located where structures 

do not protect park infrastructure, cultural landscapes, 

historic structures, or known archeological resources 

(Nordstrom and Jackson 2014). 

A solution recently suggested for Assateague Island 

National Seashore is the development of living or 

hybrid shorelines (Schupp and Coburn 2015). Such 

shorelines involve removing existing hardened 

estuarine shorelines, such as bulkheads and riprap, 

and allowing reversion of the estuarine shoreline to 

a functioning natural habitat with natural sediment 

transport processes (Nordstrom and Jackson 2013). In 

places where this is not possible, hardened structures 

could be augmented with living shoreline components. 

Living shorelines can protect vulnerable shorelines 

while also providing or enhancing coastal ecosystems, 

water quality, and wildlife habitat (Cain et al. 2009). 

The propagation of a living shoreline attempts to 

incorporate natural elements and may be nonstructural, 

such as vegetation. Along low-energy estuarine 

shorelines, native plants can buffer wave energy to 

uplands while their roots stabilize the shore and hold 

soil in place to reduce erosion. Living shorelines 

may also serve as one natural component of hybrid 

techniques, which incorporate both nonstructural 

components and traditional approaches (e.g., 

breakwaters). The structures are situated in a manner 

that does not sever the physical connection to the 

riparian, intertidal and subaqueous areas. In general, 

hybrid techniques are typically applied in places of 

medium to high wave energy whereas nonstructural 

approaches are better suited to low wave energy 

environs (Bilcovic and Mitchell 2012).

Scoping participants in 2005 and conference call 

participants in 2014, as well as scientific literature, 

noted the following recommendations for managing 

fluvial processes and erosion: 

● Perform several shoreline surveys per year to detect 

seasonal variations. This requires identifying points 

to monitor along the shorelines on both rivers. 

Update the aerial mosaics for shoreline evolution 

since 1937. Supplement these surveys with LiDAR 

(Brock et al. 2008; available at http://pubs.usgs.gov/

of/2008/1326/start.html), GIS surveys, and aerial 

photographs.

● Cooperate with state and county agencies to study 

erosion rates and processes in surrounding vicinity 

and relate to the sediment budget of the different 

watersheds.

● Dallas et al. (2013) suggest focusing future research 

on developing a quantitative system-wide sediment 

budget with data for sediment sources and sinks.
40

● Promote revegetation in areas of significant gullying 

and erosion. 

● Monitor loss of ridges within wetlands near 

Jamestown. Conduct comprehensive wetland 

mapping and monitoring throughout the park 

(Lookingbill et al. 2012).

● Monitor topographic changes due to surface and 

cliff erosion.

● Continue to promote coastal shoreline stability 

measures in places where cultural resources exist.

● Define the mappable shoreline in relation to tidal 

fluctuations. 

● Determine whether shoreline stabilization 

structures are having negative impacts on aquatic 

ecosystems in the park.

● Educate the public about potential consequences of 

erosion and other impacts associated with sea level 

rise (Lookingbill et al. 2012).

In the Geological Monitoring chapter about fluvial 

geomorphology, Lord et al. (2009) described 

additional methods for inventorying and monitoring 

geomorphology-related vital signs, including: (1) 

watershed landscape (vegetation, land use, surficial 

geology, slopes, and hydrology), (2) hydrology 

(frequency, magnitude, and duration of stream flow 

rates), (3) sediment transport (rates, modes, sources, 

and types of sediment), (4) channel cross section, (5) 

channel planform, and (6) channel longitudinal profile.

Hardaway et al. (1999a, 1999b, 2006) prepared 

shoreline management plans for specified areas within 

the park. The US ACOE (2002) presented a shoreline 

management plan for Jamestown Island that included 

a combination of sills, revetments, breakwaters, sand 

nourishment, and vegetation plantings. 

In 2012, the park submitted an environmental 

assessment to repair and stabilize the York River 

shoreline in order to protect the Colonial Parkway. 

After agency and public review, the project will be 

implemented in phases as funding allows. The project 

will include rehabilitating or installing combinations 

of shoreline treatments such as rock revetments, rock 

spurs, continuous and gap sills, pocket beaches, and 

shore-attached breakwaters between the confluence of 

Felgates Creek and the York River downstream to the 

boundary with the US Coast Guard Training Center 

Yorktown (Colonial National Historical Park 2012). 

Stormwater Management along Colonial 

Parkway and Upland Erosion

Streams and stormwater are diverted through 

114 known culverts under the Colonial Parkway, 

constructed between 1930 and 1957. Today, they clog 

easily and are inadequate to handle peak flows and 

increased runoff along the Interstate-64 (I-64) corridor 

and urban development since the 1930s. Forty percent 

of the culverts within the 152-m (500-ft) right-of-way 

maintained by the park are rated poor, critical, or 

unknown (fig. 27) (Dallas et al. 2013; Tim McLean, 

NPS Colonial National Historical Park, civil engineer, 

conference call, 12 November 2014). Sheetwash 

and gully erosion, as well as sedimentation along the 

parkway, from stormwater and runoff from surrounding 

development are an issue along the length of the 

parkway (Thornberry-Ehrlich 2005; Lookingbill et al. 

2012; GRI conference call participants, 12 November 

2014).

Impervious surfaces in upstream areas (including the 

I-64 corridor) prevent infiltration and cause pulses 

of high-energy stormwater to erode the slopes and 

overwhelm the stormwater system of the parkway; 

impervious surface areas are increasing with expanding 

urban development throughout the region (Lookingbill 

et al. 2012). From 2012 to 2014, along kilometers five 

and eight of the parkway (north of Yorktown along the 

York River), surface runoff caused significant erosion 

of the embankments, which are also undercut by storm 

and tidal action (GRI conference call participants, 12 

November 2014). In 2006, the parkway was damaged 

at Papermill Creek as a result of inadequate off-site 

stormwater control (Lookingbill et al. 2012).

Lookingbill et al. (2012) used impervious surface as a 

percentage of land area to represent human impact on 

the landscape in order to determine ecosystem impacts 

and habitat assessments They used the threshold of 

impervious surface area totaling less than 10% of 

total area to represent good ecological condition; the 

Colonial Parkway unit has more than 12% impervious 

surface and thus exceeds the threshold for good 

ecological conditions and may indicate watershed and 

habitat degradation (Lookingbill et al. 2012). 

Other than a photo inspection by the Federal Highway 

Administration in 2013, additional monitoring along 

the I-64 corridor through the park has not yet taken 

place. The park resource managers are working with 
41

Figure 27. Photographs of stormwater management structures along the Colonial Parkway. Many of the culverts 

and drains within the park are inadequate to handle the flow following common heavy precipitation. Structures are 

many decades old, cracked, and/or clogged. As impervious surfaces increase with urban development, more runoff 

is anticipated in the future. National Park Service photographs taken by Harold Pranger (NPS Geologic Resources 

Division) 28 September 2004.
42

the Federal Highway Administration and Virginia 

Department of Transportation to control runoff and 

stormwater associated with the I-64 culverts (GRI 

conference call participants, 12 November 2014). 

Plans are in place to add an additional lane to the 

I-64 corridor through the park which will increase 

impervious surface area and likely increase stormwater 

runoff. GRI conference call participants noted the need 

for adequate stormwater management measures to be 

included in any construction. The park should consider 

development of a management plan for runoff, erosion, 

and stormwater along the parkway. Geomorphologists 

at the NPS Geologic Resources Division may be able to 

assist with a technical assistance request. 

Shoreline erosion and erosion associated with 

stormwater is documented in the park. Stormwater 

erosion can also trigger or exacerbate slope movements. 

The runoff from storm events such as hurricanes erodes 

the park’s slopes, which are largely vegetated and/or 

riprapped (Thornberry-Ehrlich 2005; GRI conference 

call participants, 12 November 2014). Erosion and 

gullying can expose tree roots (fig. 28), which may 

eventually lead to the collapse of the tree and exposure 

of its rootball to further soil loss (fig. 29) or slope 

movements. This can have a significant effect on cultural 

resources, potentially exposing buried remains or 

obscuring a historic landform. Similarly, the high winds 

that accompany large storms also cause trees to fall. 

This releases pulses of sediment to streams, as well 

as removing the stabilizing effects of intact tree roots 

on park slopes. Trees blown down during Hurricane 

Isabel uplifted rootballs, affecting graves from the 

pre-settlement era through the American Civil War 

(Thornberry-Ehrlich 2005).

Figure 28. Photographs of upland erosional features in Colonial National Historical Park. Gullying and sheetwash 

erosion can impact upland areas and archeological sites. National Park Service photographs by Harold Pranger (NPS 

Geologic Resources Division), 28 September 2004.
43

Erosion along ridgelines and uplands has placed about 

60 significant cultural and/or unexcavated archeological 

sites at risk of degradation or destruction (ThornberryEhrlich 2005). Slope erosion is currently threatening 

one of the redoubts at Yorktown Battlefield (GRI 

conference call participants, 12 November 2014). 

Paleontological Resource Inventory, 

Monitoring, and Protection

As described in the “Geologic Setting and Significance” 

and “Geologic Features and Processes” chapters, fossils 

within Colonial National Historical Park are abundant, 

diverse, and historically significant.

All paleontological resources are nonrenewable and 

subject to science-informed inventory, monitoring, 

protection, and interpretation as outlined by the 

2009 Paleontological Resources Preservation Act (see 

Appendix B). As of May 2016, Department of the 

Interior regulations associated with the Act were being 

developed.

In addition to in situ fossils, fossils wash up on the 

shorelines of the York and James rivers (see inside front 

cover). Fossils cannot be collected in the park or any 

other NPS area. Unauthorized collecting likely occurs; 

however, the park does not yet have the resources 

or detailed paleontological resource survey to assess 

impacts or loss.

A field-based paleontological resource survey can 

provide detailed, site-specific descriptions and 

resource management recommendations that 

are beyond the scope of this report. Although a 

park-specific survey has not yet been completed 

for Colonial National Historical Park, a variety of 

publications and resources provide park-specific 

or servicewide information and paleontological 

resource management guidance. These are 

summarized by Tweet et al. (2014).

The management of fossils along coastlines such 

as in Colonial National Historical Park requires 

different approaches than “typical” upland 

fossil localities. Brunner et al. (2009) outlined 

these considerations and included applicable 

servicewide policy guidance to assess the full scale 

of unauthorized fossil collection and develop 

methodology to reduce the problem. 

Tweet et al. (2014) also presented the following 

preliminary recommendations:

● A dedicated paleontological inventory for Colonial 

National Historical Park would be of great value. 

The park contains substantial quantities of 

fossils that are exposed to erosion, unauthorized 

collecting, and other issues that are of management 

concern (although protective shoreline structures 

have covered many exposures), and its fossils are 

of enormous historical interest, with untapped 

educational potential. 

● Park staff should be encouraged to observe 

exposed sedimentary deposits for fossil 

material while conducting their usual duties. To 

promote this, they should also receive guidance 

regarding how to recognize common local 

fossils. When opportunities arise to observe 

paleontological resources in the field and take 

part in paleontological field studies with trained 

paleontologists, park staff should take advantage of 

them, if funding and time permit. 

● Staff members should photodocument and monitor 

(see Santucci et al. 2009) any occurrences of 

paleontological resources that may be observed 

in situ. Fossils and their associated geologic 

context (surrounding rock/sediments) should be 

documented but left in place unless they are subject 

to imminent degradation by artificially accelerated 

natural processes or direct human impacts. 

Figure 29. Photograph of exposed rootball at a fallen tree on 

Jamestown Island. Storm winds blew this tree down, exposing 

its rootball to weathering. Sediment weathered from the 

rootball washed into the nearest stream. The loss of the tree 

also may accelerate erosion by removal of the stabilizing 

roots. National Park Service photograph taken by Melanie 

Peters (NPS Geologic Resources Division) in August 2005.
44

● Fossils found in a cultural context (see Kenworthy 

and Santucci 2006) should be documented like 

other fossils. In addition, an archeologist should 

be consulted because any fossil within a cultural 

context may be culturally sensitive as well (e.g. 

subject to NAGPRA) and should be regarded as 

such until otherwise established. 

● Quaternary fossils and deposits can be used to 

describe the effects of past climate and sea level 

changes, and to predict natural responses to future 

changes. Further study of these fossils and deposits 

in and around Colonial National Historical Park is 

encouraged.

● The fate of the Banks collection, a fossil collection 

formerly on display at Colonial National Historical 

Park, should be investigated. If some or all of 

the material still exists, it could be used in a new 

exhibit. 

● Contact the NPS Geologic Resources Division for 

technical assistance with paleontological resource 

management issues. 

In the Geological Monitoring chapter about 

paleontological resources, Santucci et al. (2009) 

described five methods and vital signs for monitoring 

in situ paleontological resources: (1) erosion (geologic 

factors), (2) erosion (climatic factors), (3) catastrophic 

geohazards, (4) hydrology/bathymetry, and (5) human 

access/public use. All of these are applicable to Colonial 

National Historical Park. 

Geologic Hazards and Risks

Geologic hazards are natural or human-caused 

conditions that may impact park resources, 

infrastructure, or visitor safety. Risk is the probability 

of occurrence combined with the expected degree 

of damage or loss that may result from exposure to a 

hazard, or the likelihood of a hazard causing losses (see 

also Holmes et al. 2013). Colonial National Historical 

Park faces a variety of geologic hazards associated with 

its coastal location, including flooding and storm surge; 

those are described in previous sections of this report. 

Additional geologic hazards include slope movements 

(“landslides”), earthquakes, and radon.

Slope Movements

Slope movements are a common type of geologic 

hazard. Although a variety of movements can occur 

based on rock type, scale, trigger, and rate (fig. 13), slope 

movements are typically referred to as “landslides.” 

Bluffs of unconsolidated material are particularly 

susceptible to slope movements. For example, along 

the York River, north of Yorktown, slope failures and 

spalling required excavations to reduce the loss of 

cultural resources (GRI conference call participants, 

12 November 2014). Slope processes wash sediments 

down around Cornwallis cave, but no large failures have 

occurred there yet (GRI conference call participants, 

12 November 2014). Some bluffs have been armored to 

limit slope processes and erosion, although this limits 

the amount of sediment that is delivered to nearby 

beaches (Dallas et al. 2013). 

Shoreline erosion, erosion associated with stormwater 

control, and disturbed lands (each of which is described 

in respective sections of the report) can trigger or be 

exacerbated by slope movements. All of these are of 

great concern at Colonial National Historical Park 

because of their threats to cultural and archeological 

resources of the park. 

Anthropogenic activities can also exacerbate or cause 

slope movements. Such was the case of a 1989–1990 

slope failure below a pier in the York River near 

Yorktown. Pile driving during pier widening caused the 

slope instability, threatening the existing pier (Martin 

and Seli 1998). The movement was likely caused by a 

combination of (1) unstable, water-saturated sediments 

of the slope, (2) increased pore pressure (within the 

saturated sediments) induced by pile-driving vibrations, 

(3) a reduction in cohesive strength in the deeper 

sediments due to pore pressure increases, and (4) lateral 

displacement of the existing piles due to lateral heave of 

the Yorktown Formation (geologic map units Tymh and 

Tc) during pile driving (Martin and Seli 1998). 

Park resource management strategies to control slope 

erosion and mass wasting include natural vegetation 

barriers, no-cut zones for adjacent fields, repairing 

and expanding fencing and signing, and public service 

announcements (Rafkind 1990). Scoping participants 

in 2005 suggested developing a slope monitoring plan 

for the park; changing mowing schedules, locations, 

and techniques; and revegetating areas to decrease 

undercutting and slope erosion. Lookingbill et al. 

(2012) recommended decreasing mowing frequency. 

Martin and Seli (1998) demonstrated a test program to 

evaluate the possible mechanisms of a slope movement 

caused by pier repair near Yorktown. They installed 

slope inclinometers, pore pressure transducers, heave 
45

plates, and survey monuments to monitor the slope 

during anthropogenic activities. This information, 

combined with knowledge of the substrate, supported 

their recommendations for stable-slope development.

Wieczorek and Snyder (2009), Highland and 

Bobrowsky (2008), the US Geological Survey 

landslides website (http://landslides.usgs.gov/), and 

the NPS Geologic Resources Division Geohazards 

(http://go.nps.gov/geohazards) and Slope Movement 

Monitoring (http://go.nps.gov/monitor_slopes) 

websites provide detailed information regarding slope 

movements, monitoring, and mitigation options. In the 

Geological Monitoring chapter about slope movements, 

Wieczorek and Snyder (2009) described five vital signs 

for understanding and monitoring slope movements: 

(1) types of landslide, (2) landslide causes and triggers, 

(3) geologic materials in landslides, (4) measurement 

of landslide movement, and (5) assessment of landslide 

hazards and risks. 

Earthquakes and Fault Locations

Earthquakes are ground vibrations—shaking—that 

occurs when rocks suddenly move along a fault, 

releasing accumulated energy (Braile 2009). Earthquake 

intensity ranges from imperceptible by humans to 

total destruction of developed areas and alteration 

of the landscape. The “magnitude” of an earthquake 

refers to the amount of energy released. A variety of 

scales measure magnitude, including the Richter scale. 

Earthquakes can directly damage park infrastructure, or 

trigger other hazards such as slope movements that may 

impact park resources, infrastructure, or visitor safety. 

Park staff and residents reported shaking from the 

magnitude-5.8 earthquake that occurred in central 

Virginia, about 170 km (105 mi) northwest of Colonial 

National Historical Park, in August 2011 (US Geological 

Survey 2011; GRI conference call participants, 12 

November 2014). Shaking from that earthquake was felt 

throughout the eastern seaboard, particularly along the 

fall zone—the line marking the boundary between the 

Atlantic Coastal Plain and the Piedmont province. This 

event caused no documented damage in the park, but it 

is a reminder that earthquakes, although rare, can shake 

this region. 

Even though such large earthquakes are not common 

in the mid-Atlantic region, minor earthquakes (rarely 

felt by humans) occur along faults in southeastern 

Virginia. Inferred, buried, queried, and approximate 

fault locations are part of the GRI GIS data. It is likely 

that additional buried faults, possibly associated with 

the Chesapeake Bay impact structure, exist in the 

subsurface and may be intermittently active with small 

earthquake magnitudes (about 2.0–2.5) (ThornberryEhrlich 2005; Johnson 2007). Much of Colonial 

National Historical Park is on a subsiding (sinking) 

massive fault-bound block that is very slowly moving 

toward the impact structure (Johnson et al. 2001a). 

New faults are being revealed by drilling and mapping 

projects since the GRI GIS data were created. Recent 

studies have revealed suspected faults in the subsurface 

of the James-York Peninsula (see “Subsurface Geologic 

Features and the Chesapeake Bay Impact Structure” 

section). As with any discontinuity in the subsurface, 

these faults could move because of a large earthquake 

elsewhere, such as that which occurred in 2011 (Rick 

Berquist, Virginia Division of Geology and Mineral 

Resources, geologist, conference call, 12 November 

2014). There is a great need to accurately locate these 

faults to understand their effects on the region’s 

geomorphology and groundwater system. Drilling 

within an area of significant cultural resources must 

follow regulations for accompanying archeological 

work. The VDGMR will be working with park resource 

managers over the next several years to decide the best 

way to accurately delineate the locations of these faults 

in the park.

Any moderate earthquake has the potential to damage 

park infrastructure, cause liquefaction in the marshes, 

or trigger slope movements, although such effects are 

unlikely. According to the US Geological Survey 2009 

Earthquake Probability Map (http://geohazards.usgs.

gov/eqprob/2009/index.php; accessed 14 October 

2014), the probability that a magnitude-5.0 earthquake 

will occur near the lower James-York Peninsula in the 

next century is about 1–2% (fig. 30). These calculations 

were made prior to the 2011 earthquake in central 

Virginia, which may impact future models of earthquake 

probability. 

In the Geological Monitoring chapter about earthquakes 

and seismic activity, Braile (2009) described the 

following methods and vital signs for understanding 

earthquakes and monitoring seismic activity:

(1) monitoring earthquakes, (2) analysis and statistics 

of earthquake activity, (3) analysis of historical and 
46

prehistoric earthquake activity, (4) earthquake risk 

estimation, (5) geodetic monitoring and ground 

deformation, and (6) geomorphic and geologic 

indications of active tectonics. Braile (2009), the NPS 

Geologic Resources Division Seismic Monitoring 

website (http://go.nps.gov/seismic_monitoring), and 

the US Geological Survey Earthquakes Hazards website 

(http://earthquake.usgs.gov/) provide more information.

Radon

Radon is a heavier-than-air, colorless, odorless, 

radioactive gas, which is a natural decay product from 

also naturally occurring uranium and thorium in the 

sediments beneath the park. Long term exposure 

to elevated levels of radon creates an increased 

risk for lung cancer. Refer to the Environmental 

Protection Agency (EPA) radon website for additional 

information: http://www.epa.gov/radon/. Radon 

naturally accumulates in caves, basements, and other 

subterranean cavities. Limited air circulation in these 

spaces concentrates radon gas to levels appreciably 

higher than outside. The EPA recommended maximum 

level of radon gas concentration is 4 picocuries per liter 

(pCi/L) (EPA 2013). 

Sediments at the base of the Yorktown Formation where 

it overlies the Eastover Formation (geologic map unit Tc) 

commonly contain an accumulation of marine mammal 

bone enriched in phosphate and uranium. High levels 

of radon have been found in dwellings built within or 

just above this contact (Rick Berquist, Virginia Division 

of Geology and Mineral Resources, geologist, written 

communication, 24 August 2015). Tegan et al. (1991) 

tested radon levels in buildings and adjacent ground 

Figure 30. Probability map of earthquakes with magnitude greater than 5.0. This probability assumes a 100-year 

timespan and a 50-km (30-mi) radius around Colonial National Historical Park, Virginia (green star). Purple star 

represents the approximate epicenter of the 5.8-magnitude earthquake from 2011; however these data are from a 

2009 model and thus predate this event. Graphic was generated by the US Geological Survey earthquake probability 

mapping program (https://geohazards.usgs.gov/eqprob/2009/index.php, accessed 14 October 2014) and annotated by 

Trista L. Thornberry-Ehrlich (Colorado State University).
47

in James City County, near Williamsburg. Buildings 

located on the Bacons Castle Formation (Qbc), Shirley 

Alloformation (Qsh), and Yorktown Formation (Tymh

and Tc) had elevated radon levels approaching the EPA 

recommended maximum level. Radon levels in the 

ground adjacent to these buildings were much higher 

than those in buildings themselves. Monitoring and 

ventilation remediate radon threats. 

Groundwater Quantity and Quality

Since the establishment of the first colony at 

Jamestowne, access to fresh groundwater has been a 

priority and brackish incursions may have forced the 

abandonment of the agricultural endeavors on the 

island (Johnson et al. 1995). There is a great need to 

understand how groundwater is percolating through 

the subsurface system of interlayered, discontinuous 

aquifers and confining units (see “Hydrogeologic 

System at Yorktown Battlefield” section) because 

groundwater from the shallow aquifer system can 

contribute more than half of the flow in the park 

vicinity’s streams and a large part of the water in the 

wetlands. The stream and wetland features provide (1) 

critical habitat for rare, threatened, and endangered 

species; (2) nurseries for important local fish species; 

and (3) opportunities for education, observation, and 

recreation (Speiran and Hughes 2001; Lookingbill et al. 

2012). Groundwater in sinkhole complexes at Yorktown 

is critical to those habitats. Seasonal groundwater pulses 

also help to purge pore water (water among sediment 

grains) of accumulated salt and to export material to 

adjacent estuaries (Tobias et al. 2001a). If groundwater 

quantity or quality is compromised, the negative effects 

will ripple through the entire stream and wetland 

system.

Factors affecting groundwater-level fluctuations 

are complex and include variations in rainfall and 

evapotranspiration, aquifer rock types, geologic 

structures, tidal fluctuations, sea level rise, and human 

activity (Brockman et al. 1997; GRI conference call 

participants, 12 November 2014). Droughts and human 

water-use have the potential to deplete the shallow 

aquifer system. Depletions of the aquifer can also 

cause brackish water incursions from the adjacent tidal 

rivers. This situation is exacerbated by sea level rise (see 

“Sea Level Rise, Flooding, and Coastal Vulnerability” 

section). Adjacent urban developments have already 

changed the groundwater levels. Impervious surfaces 

associated with urban landscapes increase surface 

runoff and stormwater problems (see “Stormwater 

Management along Colonial Parkway and Upland 

Erosion” section). New residential, commercial, 

or industrial developments may threaten both the 

availability and quality of groundwater in the park. 

The colonial Greenspring, (see plate 1) an early water 

source for colonists, is an location of particular concern 

(Thornberry-Ehrlich 2005).

According to Speiran and Hughes (2001), the relatively 

deep Yorktown-Eastover aquifer has the potential to 

transport groundwater contaminants from sources 

outside the park boundaries into the park. Surface 

and groundwater contamination from surrounding 

lands is a major stressor for the park and park water 

was contaminated by several fuel spills on adjacent 

properties (Lookingbill et al. 2012). Both the Naval 

Weapons Station Yorktown and the Naval Field 

Station are mitigating hazardous materials sites (GRI 

conference call participants, 12 November 2014). 

According to Brockman et al. (1997), the hydrogeologic 

system of the weapons station station is similar to 

that of Yorktown with the same six units including 

the Columbia, Cornwallis cave, and YorktownEastover aquifers. However, given the groundwater 

divides (i.e., a ridge in the water table from which 

the groundwater moves away in both directions) and 

the dissected, discontinuous nature of the shallow 

aquifers (due in part to the Chesapeake Bay impact 

structures), contamination potential from outside 

sources is considered low (Powars and Bruce 1999; 

Speiran and Hughes 2001). Despite this low potential, 

water monitoring has detected contaminants in the 

groundwater near Yorktown (GRI conference call 

participants, 12 November 2014).

Knowledge of groundwater ages and recharge rates 

helps to constrain groundwater-flow models within the 

shallow water aquifer system and can help remediation 

activities by providing estimates of the speed at which 

contamination moves through the hydrogeologic system 

and how this varies spatially (Nelms et al. 2001). Dating 

of shallow-aquifer groundwater in the nearby Naval 

Weapons Station Yorktown by Nelms et al. (2001) using 

chlorofluorocarbons gave an age range of one to 48 

years with a median age of 10 years. The youngest water 

was from the unconfined Columbian aquifer and the 

oldest water was from the Yorktown-Eastover aquifer 

(see fig. 19). The confining units between the aquifers 

are leaky, allowing for vertical movement over the span 
48

of decades. Most recharge occurs during winter. 

Colonial National Historical Park does not have a 

groundwater management plan (GRI conference call 

participants, 12 November 2014). A comprehensive 

understanding of the connections between the 

groundwater and surface-water features would 

facilitate management of the quantity and quality of 

water in the park’s streams, wetlands, and associated 

riparian habitats. Water quality is a natural resource 

assessed by Lookingbill et al. (2012). Delineation 

of the hydrogeologic framework using borehole 

and geophysical logs, as well as geologic maps allow 

the conceptualization of the physical constraints 

that control the flow of groundwater and potential 

contaminants (Speiran and Hughes 2001). McFarland 

and Bruce (2006) presented a hydrogeologic framework 

for the Virginia Coastal Plain, but given the inherent 

spatial variability of the subsurface units and geologic 

structures, creating and refining a park-specific model 

would provide more pertinent information. Sources 

of information regarding groundwater in the vicinity 

include Brockman et al. (1997), who delineated the 

groundwater system at the Naval Weapons Station 

Yorktown outside the park. Tobias et al. (2001a) 

quantified groundwater discharge and seasonal 

variability through fringing wetlands at the Ringfield 

study site within Colonial National Historical Park 

at the confluence of Kings Creek and the York River 

(see plate 1). Their methodology could potentially be 

applied to other wetlands within the park to better 

understand the groundwater input. 

Long-term monitoring of the system would provide 

information for evaluating long- and short-term trends 

(Speiran and Hughes 2001). Speiran and Hughes 

(2001) recommended future research on the Yorktown 

Battlefield aquifer system that could be expanded to the 

entire park with further study and installation of more 

wells for management of the water resources. Their 

suggestions included (1) continued development of the 

hydrogeologic framework (including installing more 

wells); (2) monitoring groundwater levels and quality, 

rates of discharge at springs, stream flow, and stream 

water quality; and (3) evaluation of the connections 

between the shallow aquifer system and the streams, 

wetlands, and riparian habitats. 

Detailed water quality discussions are beyond the 

scope of this report. The park helped to prepare a water 

resources management plan in 1994 that sought to guide 

water resources-related activities over the following 10 

years (Virginia Institute of Marine Science and National 

Park Service 1994). McFarland (2010) presented a 

groundwater-quality data and regional trends report for 

the Virginia Coastal Plain dating back to 1906. Contact 

the NPS Water Resources Division: http://www.nature.

nps.gov/water/ for more information and assistance. 

Karst Landscape Management

Cornwallis “cave” is not a natural feature and is 

managed as an abandoned mineral lands feature as 

described in the “Abandoned Mineral and Disturbed 

Lands” section of the report. 

Karst features including sinkholes, subtle depressions, 

and karstic wetlands dot the landscape within and 

adjacent to the park (see “Karst Topography and 

Cornwallis ‘Cave’” section). Karst forms in carbonaterich layers within geologic map units Tymh and Tc. 

Sinkhole formation locally extends both laterally 

and vertically. A karstic wetland developed in the 

yard of a home in the Queens Lake subdivision near 

Williamsburg and sinkhole formation may threaten the 

stability of infrastructure throughout the park region 

(Rick Berquist, geologist, Virginia Division of Mineral 

Resources, professional communication, August 2005). 

With the increase in urban development adjacent to 

the park, particularly at Yorktown Battlefield, there 

may be long-term impacts to karst features within the 

park such as sinkholes and springs (GRI conference 

call participants, 12 November 2014). Karst features 

connect to the groundwater system. The quantity 

and quality of groundwater resources are additional 

resource management considerations addressed in that 

section of this report. 

Yorktown Formation Shrink-and-Swell Clays

A layer of clay-rich silt, typically between 2 to 3 m (7 to 

10 ft) thick, at the top the Yorktown Formation (Tymh

and Tc) restricts groundwater flow as an “aquitard” 

and can shrink or swell depending on water content 

(Thornberry-Ehrlich 2005). Other so-called “shrinkand-swell clays” are present in the Morgarts Beach 

Member of the Yorktown Formation (see figs. 3 and 15) 

(Rick Berquist, conference call, 12 November 2014). 

Shrink-and-swell issues arise from the clay minerals 

absorbing water and expanding, then shrinking as 

they dry. This change in volume impacts roads, trails, 

building foundations, and other infrastructure. For 

example, the clays of the Yorktown Formation cause 
49

significant problems in recent road and building 

developments near Williamsburg, including the Queens 

Lake subdivision (Thornberry-Ehrlich 2005). Areas 

underlain by the uppermost Yorktown Formation 

should be assessed by a geologist when planning new 

infrastructure or modifying existing facilities. 

Abandoned Mineral and Disturbed Lands

According to the NPS Abandoned Mineral Lands 

(AML) database (accessed 26 September 2014) and 

Burghardt et al. (2014), Colonial National Historical 

Park contains one AML feature at one site: Cornwallis 

“cave”, which was excavated into coquina of the 

Yorktown Formation (geologic map units Tymh and 

Tc). The roof of Cornwallis cave is failing as moisture 

within the cave is increasing due to the sealing of the 

openings long ago. The park has requested a condition 

assessment from geomorphologists with the NPS 

Geologic Resources Division.

Additional potential AML features such as auger holes, 

clay pits, quarries, sand and gravel pits, sand pits, and 

test holes are in the area. Test holes, sand and gravel 

pits, and marl quarries exist within park boundaries. 

“Marl” is a calcium carbonate and clay-rich mudstone 

often used as a source of lime or building material. Park 

staff are unsure of the vintage of these features, but they 

could be added to the AML database if appropriate.

AML features typically present a variety of resource 

management issues such as visitor and staff safety and 

environmental quality of air, water, and soil (Burghardt 

et al. 2014). AML features can also provide habitat for 

bats and other animals. Resource management of AML 

features requires an accurate inventory and reporting. 

All AML features should be recorded in the AML 

database (the NPS Geologic Resources Division may 

be able to provide assistance). An accurate inventory 

can identify human safety hazards, and facilitate 

closures, reclamation, and restoration of AML features 

(Burghardt et al. 2014). When appropriate for resource 

management and visitor safety, AML features can also 

present opportunities for interpretation as cultural 

resources. The NPS AML Program website, http://

go.nps.gov/aml, provides further information.

Because Colonial National Historical Park is a narrow 

corridor across the heavily developed James-York 

Peninsula, adjacent land use can potentially negatively 

impact park resources. Disturbed areas surrounding 

the park region include several “Superfund” sites along 

the I-64 corridor; the Naval Weapons Station Yorktown 

Pier which disrupts sedimentation patterns; the preWorld War II Navy Mine Depot, Yorktown leaking 

contaminants such as acids, mercury, and heavy metals; 

and a location near Ballard Creek, which may be a 

source of mercury contamination (Thornberry-Ehrlich 

2005; Global Security 2011; EPA 2015). Status of the 

“Superfund” sites is available from the EPA website: 

https://www.epa.gov/superfund/search-superfundsites-where-you-live (accessed 11 March 2015). 

According to the VDGMR, an abandoned borrow 

pit along the Colonial Parkway associated with the 

construction of I-64 has caused significant erosion 

problems as it channelizes surface water through 

park property, under the parkway, and into the York 

River. This setting alters water flow to and through 

the surrounding riparian ecosystem through park 

property. A GRD geologist visited the site in 2004 

to suggest reclamation and stabilization options for 

the site. No formal monitoring of the area has taken 

place and erosion continues to be a problem along the 

parkway (see “Stormwater Management along Colonial 

Parkway” section) (GRI conference call participants, 12 

November 2014).

Land use practices and visitor activities create disturbed 

areas that accelerate erosion which may impact park 

resources. Areas of heavy foot traffic, unofficial social 

trail use, mountain bike and off-road vehicle traffic, 

and overmowing expose soil and are susceptible to 

erosion on even moderate slopes (Thornberry-Ehrlich 

2005; Lookingbill et al. 2012). Day and overnight 

use pose threats to stabilizing sand dune vegetation 

(Lookingbill et al. 2012). Erosion and downward 

movement of earth material occurs naturally along 

the slopes within the park, but informal trails along 

the Yorktown bluffs—containing remains of the 

British and Civil War earthworks—eroded the bluffs 

(Rafkind 1990). Camping, canoeing and kayaking, 

swimming, and hunting are not permitted in the park, 

and yet occur in forested lands and along beaches and 

shoreline (Lookingbill et al. 2012). These activities 

trample vegetation and soils, and contribute to erosion 

(Lookingbill et al. 2012). Walking, biking, or horseback 

riding that originate in adjacent land often result in the 

creation of unplanned trails, leading to trampling and 

erosion of natural resources (Lookingbill et al. 2012). 

Sheet erosion and gully erosion are both caused by 

these user impacts (Lookingbill et al. 2012).

51

Geologic History

This section describes the chronology of geologic events that formed the present landscape of Colonial 

National Historical Park.

The geologic history of Colonial National Historical 

Park includes the formation of a supercontinent, 

the construction and erosion of a massive mountain 

chain, the deposition of sediment along a coastline 

with fluctuating sea level, a spectacular bolide impact, 

and development of the modern Chesapeake Bay and 

tributary river systems.

Three Paleozoic Era orogenies (mountain building 

periods)—the Taconic (440 million to 420 million years 

ago), the Acadian-Neoacadian (360 million years ago), 

and the Alleghany (325 million to 265 million years 

ago)—culminated in the uplift of the Appalachian 

Mountains and the formation of the supercontinent 

Pangaea. Pangaea incorporated all of the major 

continents in existence. The Appalachian Mountains 

traversed the interior of the supercontinent (fig. 31A), 

and may have rivaled the modern Himalayas with 

elevations potentially exceeding 6,100 m (20,000 ft) 

(Means 1995; Harris et al. 1997; Southworth et al. 2009). 

Pangaea was not to last but endured for about 80 million 

years. 

Mesozoic Era (252.2 million to 66.0 million 

years ago)—Origin of the Coastal Plain

During the Late Triassic Epoch, approximately 

185 million years ago after the Allegany Orogeny 

(Southworth et al. 2009), the supercontinent Pangaea 

began pulling apart (rifting) into landmasses that would 

form the modern continents. As the African continent 

moved away from North America the Atlantic Ocean 

began to form (fig. 32); extension of the Earth’s crust 

created down-dropped basins (grabens; see fig. 17) 

along the eastern margin of North America (Harris et 

al. 1997; Southworth et al. 2008). The Culpeper basin, 

home to Manassas National Battlefield Park (see GRI 

report by Thornberry-Ehrlich 2008), is one example of 

a Triassic extension basin. 

Because collisional tectonic forces ceased during rifting, 

the Appalachian Mountains were no longer being 

pushed upward and erosion became the dominant 

process shaping the mountains. Erosion and weathering 

since the end of the Alleghany Orogeny may have 

removed about 6.5 km (4.0 mi) of rock (Southworth 

et al. 2009). Immense amounts of gravel, sand, and 

silt spread eastward to form the Atlantic Coastal Plain 

(fig. 31B) (Duffy and Whittecar 1991; Ramsey 1992; 

Whittecar and Duffy 2000; Southworth et al. 2008). The 

lowermost unit covering the bedrock and underlying 

most of the Coastal Plain is the Early Cretaceous 

Potomac Formation (145.5 million to 66.0 million 

years old) overlain by the progressively younger Aquia, 

Marlboro Clay, Nanjemoy, Piney Point, Chickahominy, 

Old Church, Calvert, Choptank, and St. Marys 

formations (Johnson et al. 2001a). As sea level rose and 

fell, deposition took place in a variety of environments 

such as marine, coastal, fluvial, and terrestrial.

Cenozoic Era (66.0 million years ago to 

present)—Building and Reshaping the Coastal 

Plain

Deposition of Coastal-Plain sediments was largely 

continuous and undisturbed until 35 million years 

ago when a meteor or comet impacted the continental 

shelf near the location of the modern mouth of the 

Chesapeake Bay (fig. 31C) (Poag et al. 1991; Poag 1997; 

Johnson et al. 1998; Powars and Bruce 1999). Estimates 

vary, but the crater may have been as large as 90 km 

(56 mi) across and 1.3 km (0.8 mi) deep (Poag 1997; 

Collins and Wünnermann 2005). The outer rim of the 

crater structure passes through Yorktown (fig. 18). 

The impact deformed the stack of Cretaceous (145.0 

million to 66.0 million years ago), Paleocene (66.0 

million to 56.0 million years ago), and Eocene (56.0 

million to 33.9 million years ago) sediments that formed 

the Coastal Plain at that point in time. A succession of 

tsunamis swept across the Coastal Plain and Piedmont, 

causing the crater to fill with water-saturated debris. 

An impact breccia formed in the sediments and a lens 

of saltwater entered the breccia, causing permanent 

deep-groundwater salinity. The impact crater was a 

topographic low (i.e., depositional basin) for millions 

of years. Blocks of sediment slumped into the crater 

causing juxtaposition of sedimentary units of different 

age—angular unconformities (see fig. 18). The crater 

also strongly affected the positions and development of 

the York and James rivers, as well as the Chesapeake Bay 

(Poag 1997; Johnson et al. 1998; Tweet et al. 2014). 
52

Figure 31A–C. Illustration of the evolution of the landscape and geologic foundation of Colonial National Historical 

Park. Graphics are not to scale. Colors are standard colors approved by the US Geological Survey to indicate different 

time periods on geologic maps, and correspond to the colors on the Map Unit Properties Table. Map symbols are 

included for the geologic map units mapped within the park. Figure continues on next page. Graphic by Trista L. 

Thornberry-Ehrlich (Colorado State University). 
53

Figure 31D–F. Illustration of the evolution of the landscape and geologic foundation of Colonial National Historical 

Park, continued. Graphics are not to scale. Colors are standard colors approved by the US Geological Survey to indicate 

different time periods on geologic maps, and correspond to the colors on the Map Unit Properties Table. Map symbols 

are included for the geologic map units mapped within the park. Graphic by Trista L. Thornberry-Ehrlich (Colorado 

State University). 
54

The development of the landscape at Colonial National 

Historical Park was primarily affected by the deposition 

of Miocene (23.0 million to 5.3 million years ago; part of 

the Tertiary) and younger sediments in shallow marine, 

estuarine, and fluvial settings on a shallow shelf near the 

western edge of the crater (Brockman et al. 1997). Given 

the proximity of the sediments to sea level, fluctuations 

in global sea level profoundly affected the types that 

were deposited or eroded away from the landscape. The 

oldest unit (more than 5.3 million years old) mapped 

within the park is the Late Miocene Eastover Formation 

(part of geologic map unit Tc) (Bick and Coch 1969; 

Johnson 1972; Berquist 2010). After a period of erosion 

marked by a disconformable contact, the Eastover 

Formation accumulated in a mosaic of marine shelf, 

marginal marine, and nonmarine environments in two 

distinct episodes: an older, cooler, open marine phase, 

and a younger, subtropical, shallow marine phase (Ward 

and Blackwelder 1980; Newell and Rader 1985). 

Figure 32. Paleogeographic maps of North America. The red star indicates the approximate location of Colonial 

National Historical Park. Graphic complied by Trista L. Thornberry-Ehrlich (Colorado State University). Base 

paleogeographic maps created by Ron Blakey (Colorado Plateau Geosystems, Inc.), which are available at

http://cpgeosystems.com/index.html (accessed 24 September 2014).
55

Following deposition of the Eastover Formation, the 

Pliocene Yorktown Formation (5.3 million to 2.6 million 

years old; Tymh and Tc), was deposited in primarily 

temperate-climate, marine settings (fig. 31D) (Bick and 

Coch 1969; Johnson 1972; Berquist 2010; Winkelstern 

et al. 2013). The first marine advance during Yorktown 

deposition eroded the Eastover Formation surface and 

deposited the lower Yorktown Formation (Newell and 

Rader 1985). A series of marine transgressions caused 

open-shallow marine, restricted marine (lagoons or 

bays), shell reefs, and barrier bars to shift around on the 

landscape collecting a complex record of characteristic 

sediments (Ward and Blackwelder 1980; Campbell 

1993; Tweet et al. 2014). This setting was further 

complicated by the movement of still-active faults 

associated with the Chesapeake Bay impact structure. 

This caused certain submerged areas to rapidly 

uplift with respect to others, creating shallow-water 

environments that supported abundant marine life 

(now preserved as fossils). Waves and currents broke 

shells into sand-sized pieces. The shell hash then moved 

landward during sea level advances (Johnson et al. 1998; 

Johnson 2007).

During the Pleistocene Epoch, global climate shifts 

brought alternating periods of prolonged cold—ice 

ages—and relative warmth similar to modern climate. 

Continental ice sheets descended south from the Arctic, 

reshaping the landscape of much of the northern 

United States. Though glaciers from the Pleistocene ice 

ages never reached southeastern Virginia (the southern 

terminus was in central Pennsylvania), the colder 

climates of the ice ages played a role in the deposition 

of sediments underlying Colonial National Historical 

Park. During glacial advances, global sea level dropped 

as ocean water was entrained as ice. Weathering 

in the Appalachian Mountains was accelerated in 

the periglacial setting, supplying massive pulses of 

sediments to be reworked by streams and waves 

during warmer periods (Ramsey 1992). During cooler 

periods, the Pleistocene rivers carved deep channels 

and deposited fluvial gravels (fig. 31E) (Johnson et al. 

2001a). The James River was at least 70 m (230 ft) below 

its present level (Johnson 2007). During interglacial 

warm periods, global sea level rose as the ice melted and 

the river canyons were flooded. These shifts in climate 

also changed which organisms were present (e.g., 

subtropical faunas in the Yorktown Formation followed 

by significant local extinctions in the Pleistocene) 

(Stanley 1986; Williams et al. 2009; Tweet et al. 2014). 

The units deposited atop the Yorktown Formation 

(Tch, Qbc, Qm, Qw, Qcc, Qc, Qsh, Qtp, Qtlp, Qtl, Qts, 

and Qt) record a complex history of sea level change 

and shifting depositional environments and climates 

(table 4). Broadly, the transition was from typical 

marine settings to fluvial-estuarine (Ramsey 1992). As 

mentioned in the “Coastal Plain Sediments” section, 

the interrelationships and interpretations of these units 

are still the subject of debate and study. A complete, 

conformable sequence of these deposits does not exist 

owing to their spatial complexity (Bick and Coch 1969; 

Tweet et al. 2014). In some places, the boundaries 

between units are not clear, causing groupings of 

mapped units, for example, the Tabb Alloformation, 

Lynnhaven and Poquoson members, undifferentiated 

Table 4. Climate and depositional setting for map units occurring within Colonial National Historical Park.

Age Geologic Map Unit Unit Symbol Climate Depositional Setting

Quaternary

Tabb Alloformation Qt, Qtp, Qtlp, 

Qtl, and Qts Cooler Fluvial, estuarine, and marginal restricted marine

Elsing Green Alloformation Qeg Cooler Fluvial, estuarine?

Shirley Alloformation Qsh Warmer Fluvial, estuarine, and nearshore marine

Windsor Formation Qw Warmer Fluvial, estuarine, tidal flat, and restricted marine

Bacons Castle Formation Qbc Cooler Fluvial, estuarine, tidal flat, and possibly marine

Tertiary

Cold Harbor Formation Tch Warmer Marginal marine, wave-dominated delta, shallow 

marine, tidal flats, tidal channels

Yorktown Formation Tymh and Tc Subtropical Shallow marine, open marine, lagoon, restricted 

marine, barrier

Eastover Formation Tc Cooler/

Subtropical Shallow marine

Note: Units listed with oldest on bottom and youngest on top. Refer to Map Unit Properties Table for more information.
56

(Qtlp). This grouped unit spans all but the most recent 

deposits of the entire stratigraphic column (see fig. 3) 

of units presented in the GRI GIS data (Berquist 2010). 

During sea level highstands, marine and estuarine 

deposits dominated in broad shelves throughout the 

region. Between marine transgressions, when climates 

were generally cooler and sea level dropped, eroded 

surfaces and deep channel incisions dominated, 

forming dissected terrains. Complex arrangements 

of erosional scarps and channel fills developed. The 

youngest deposits at Colonial National Historical Park 

are found at the lowest elevations, along riverways, close 

to sea level, deposited during a Holocene fill episode 

(Bick and Coch 1969; Johnson and Berquist 1972; 

Berquist 2010; Tweet et al. 2014). 

Modern deposits are still accumulating and being 

reworked by Earth surface processes on the Colonial 

National Historical Park landscape today (fig. 31F). 

Sands (Qsg, Qsnd), beach and dune (Qb), shelly bottom 

sediments (Qshom), and alluvial deposits (Qaly, Qalo) 

accumulate in high-energy environments such as river 

channels, and wave-worn shorelines. Quiet-water 

environments such as wetlands and lagoons collect 

organic-rich, fine-grained sediments (Qms, Qss, Qom) 

such as mud and peat (Berquist 2010). Estuarine 

deposition began less than 5,000 years ago when the 

rivers became tidal; local marshes had formed by at 

least 3,000 years ago (Sager et al. 1994; Johnson 2007). 

For more than 10,000 years, humans have been present 

in the park vicinity, leaving a record of their activities 

(National Park Service 2001). Humans have been 

changing the landscape at Colonial National Historical 

Park in myriad ways. Mappable areas of artificial fill or 

disturbed earth materials (Qf) occur within the GRI GIS 

map data (Berquist 2010).
57

Geologic Map Data

This chapter summarizes the geologic map data available for Colonial National Historical Park.

A poster (in pocket) displays the GRI GIS data draped over imagery of the park and vicinity. The Map 

Unit Properties Table (in pocket) summarizes this report’s content for each map unit in the GRI GIS 

data. Complete GIS data are available at the GRI publications website: http://go.nps.gov/gripubs.

Geologic Maps

Geologic maps facilitate an understanding of an area’s 

geologic framework and the evolution of its present 

landscape. Using designated colors and symbols, these 

maps portray the spatial distribution and temporal 

relationships of rocks and unconsolidated deposits. The 

American Geosciences Institute website, http://www.

americangeosciences.org/environment/publications/

mapping, provides more information about geologic 

maps and their uses.

Source Maps

The GRI team digitizes paper maps and converts 

digital data to conform to the GRI GIS data model. 

The GRI GIS product includes essential elements 

of the source maps such as map unit descriptions, a 

correlation chart of units, a map legend, map notes, 

cross sections, figures, and references. The GRI team 

used the following source to produce the GRI GIS data 

for the park. This map also provided information for 

this report.

Berquist, C. R., Jr. 2015. Geologic Map of the 

Williamsburg 30- x 60-minute Quadrangle, Virginia 

(scale 1:100,000). Unpublished. Virginia Division 

of Geology and Mineral Resources, Charlottesville, 

Virginia.

GRI GIS Data

The GRI team implements a GIS data model that 

standardizes map deliverables. The data model is 

included on the enclosed CD and is also available 

at http://go.nps.gov/gridatamodel. This data model 

dictates GIS data structure, including layer architecture, 

feature attribution, and relationships within ESRI 

ArcGIS software. The GRI team digitized the data for 

Lake Meredith National Recreation Area and Alibates 

Flint Quarries National Monument using data model 

version 2.2. The GRI Geologic Maps website,

http://go.nps.gov/geomaps, provides more information 

about GRI map products. 

GRI GIS data are available through the NPS Integrated 

Resource Management Applications (IRMA) portal 

(https://irma.nps.gov/App/Portal/Home). Enter “GRI” 

as the search text and select a park from the unit list.

The following components are part of the GRI GIS 

data:

● A GIS readme file (colo_gis_readme.pdf) 

that describes the GRI data formats, naming 

conventions, extraction instructions, use 

constraints, and contact information;

● Data in ESRI geodatabase GIS format;

● Layer files with feature symbology (table 5);

● Federal Geographic Data Committee (FGDC)–

compliant metadata;

● An ancillary map information document (colo_

geology.pdf) that contains information captured 

from source maps;

● An ESRI map document (colo_geology.mxd) that 

displays the digital geologic data; and

● A version of the data viewable in Google Earth 

(colo_geology.kmz; see table 5).

GRI Poster

A poster of the GRI GIS data draped over a shaded 

relief image of the park and vicinity is included with this 

report. Geographic information and park features have 

been added to the poster. Elevation data and added 

geographic information are not included in the GRI GIS 

data, but are available from a variety of sources. Contact 

the GRI team to locate these data.

Table 5. Geology data layers in the Colonial National 

Historical Park GIS data.

Data Layer On 

Poster?

Google 

Earth Layer?

Impact Structure Lines Yes Yes

Faults Yes Yes

Geologic Contacts No Yes

Geologic Units Yes Yes
58

Map Unit Properties Table

The Map Unit Properties Table lists the geologic time 

division, map symbol, and a description for each of 

the geologic map units in the GRI GIS data. Following 

the structure of the report, the table summarizes the 

geologic features, processes, resource management 

issues, and history associated with each map unit.

Use Constraints

Graphic and written information provided in this 

report is not a substitute for site-specific investigations. 

Ground-disturbing activities should neither be 

permitted nor denied based upon the information 

provided here. Please contact the GRI team with any 

questions.

Minor inaccuracies may exist regarding the locations 

of geologic features relative to other geologic or 

geographic features in the GRI GIS data and on the 

poster. Based on the source map scale (1:100,000) and 

US National Map Accuracy Standards, geologic features 

represented in the GRI GIS data are expected to be 

horizontally within 51 m (167 ft) of their true locations.
59

Glossary

These are brief definitions of selected geologic terms relevant to this report. Definitions are based on 

those in the American Geosciences Institute Glossary of Geology (5th edition; 2005). Additional terms 

are defined at http://geomaps.wr.usgs.gov/parks/misc/glossarya.html.

abandoned mineral lands (AML). Lands, waters, and 

surrounding watersheds that contain facilities, 

structures, improvements, and disturbances associated 

with past mineral exploration, extraction, processing, 

and transportation, including oil and gas features and 

operations, for which the National Park Service takes 

action under various authorities to mitigate, reclaim, 

or restore in order to reduce hazards and impacts to 

resources.

abandoned mineral lands (AML) feature. An individual 

element of an AML site, such as vertical shaft, adit, open 

stope, open pit, highwall, and prospect. Features include 

structures such as headframes, mills, wellheads, and 

storage facilities; landform modifications such as access 

roads, drainage diversions, and drill pads; and piles of ore, 

protore (marginal-grade ore), waste rock, soil stockpiles, 

and hardrock or placer tailings.

abandoned mineral lands (AML) site. An area composed of 

AML features grouped by past ownership, geographical, 

or other logical grouping containing facilities, structures, 

improvements, and disturbances associated with 

past mineral exploration, extraction, processing, and 

transportation operations.

accretion (sedimentary). The gradual addition of new land 

to an existing landmass by the deposition of sediment, for 

example, on a beach by the washing up of sand from the 

sea.

accretion (streams). The filling-up of a stream channel as a 

result of such factors such as silting or wave action.

adit. A horizontal passage into a mine from the surface.

aeolian. Describes materials formed, eroded, or deposited 

by or related to the action of wind. 

alluvial fan. A low, relatively flat to gently sloping, fanshaped mass of loose rock material deposited by a stream, 

especially in a semiarid region, where a stream issues from 

a canyon onto a plain or broad valley floor.

alluvium. Stream-deposited sediment.

aquiclude. A saturated geologic unit that is incapable of 

transmitting significant quantities of water under ordinary 

hydraulic gradients. Replaced by the term “confining 

bed.”

aquifer. A rock or sedimentary unit that is sufficiently 

porous to hold water, sufficiently permeable to allow 

water to move through it, and saturated to some level.

aragonite. A carbonate (carbon + oxygen) mineral of 

calcium, CaCO3; the second most abundant cave mineral 

after calcite, differing from calcite in its crystal structure.

astronomical tide. The periodic rise and fall of a body of 

water resulting from gravitational interactions between 

the Sun, Moon, and Earth. Synonymous with “tide,” but 

used to emphasize the absence of atmospheric influences.

bank. A submerged ridge of sand in the sea, a lake, or a river, 

usually exposed during low tide or low water.

barrier island. A long, low, narrow island consisting of a 

ridge of sand that parallels the coast.

base flow. Streamflow supported by groundwater and not 

attributed to direct runoff from precipitation or snow 

melt.

base level. The lowest level to which a stream channel can 

erode. The ultimate base level is sea level, but temporary, 

local base levels exist. 

basement. The undifferentiated rocks, commonly igneous 

and metamorphic, that underlie rocks exposed at the 

surface, commonly sedimentary. In many regions the 

basement is of Precambrian age, but it may be much 

younger. Also, Earth’s crust below sedimentary deposits 

that extends down to the Mohorovicic discontinuity.

basin (structural). A doubly plunging syncline in which 

rocks dip inward from all sides.

basin (sedimentary). Any depression, from continental to 

local scale, into which sediments are deposited.

bathymetry. The measurement of ocean or lake depths and 

the charting of the topography of the ocean or lake floor. 

beach. The unconsolidated material at the shoreline that 

covers a gently sloping zone, typically with a concave 

profile, extending landward from the low-water line to 

the place where there is a definite change in material 

or physiographic form (e.g., a cliff), or to the line of 

permanent vegetation (usually the effective limit of the 

highest storm waves).

bed. The smallest sedimentary stratigraphic unit, commonly 

ranging in thickness from about 1 cm (0.4 in) to 1 to 2 m 

(40 to 80 in) and distinguishable from beds above and 

below.

bedding. Depositional layering or stratification of 

sediments.

bedrock. Solid rock that underlies unconsolidated 

sedimentary deposits and soil.

benthic. Pertaining to the ocean bottom or organisms living 

on or in substrate; also, referring to that environment.

bivalve. Having a shell composed of two distinct, but equal 

or nearly equal, movable valves, which open and shut.

block (fault). A crustal unit bounded completely or partially 

by faults.

body fossil. Evidence of past organisms such as bones, teeth, 

shells, or leaf imprints. 

breakwater. Shore-parallel structures that reduce the 

amount of wave energy reaching a harbor or stretch of 

shoreline located behind the structure. Breakwaters are 

similar to natural bars, reefs or nearshore islands and are 

designed to dissipate wave energy. The reduction in wave 
60

energy causes sediment deposition in the sheltered area 

behind the breakwater.

breccia. A coarse-grained, generally unsorted sedimentary 

rock consisting of cemented angular clasts more than 2 

mm (0.08 in) across. 

brecciation. Formation of a breccia, as by crushing or 

breaking a rock into angular fragments.

bulkhead. Vertical structures or partitions, usually running 

parallel to the shoreline, for the purpose of retaining 

upland soils while providing protection from wave action 

and erosion.

burrow. A tubular or cylindrical hole or opening, made in 

originally soft or loose sediment by a mud-eating worm, 

mollusk, or other invertebrate; may be later filled with clay 

or sand and preserved.

calcareous. Describes a substance that contains calcium 

carbonate. When applied to a rock name it implies that as 

much as 50% of the rock is calcium carbonate.

calcium carbonate. CaCO3. A solid occurring in nature as 

primarily calcite and aragonite. 

calcite. A carbonate (carbon + oxygen) mineral of calcium, 

CaCO3; calcium carbonate. It is the most abundant cave 

mineral.

cape. An extensive, somewhat rounded irregularity of land 

jutting out from the coast into a large body of water, either 

as a peninsula (e.g., Cape Cod, Massachusetts) or as a 

projecting point (e.g., Cape Hatteras, North Carolina). 

Also, the part of the projection extending farthest into the 

water.

carbonate. A mineral group composed of carbon and 

oxygen plus an element or elements; for example calcite, 

CaCO3

; and dolomite, CaMg(CO3)2.

carbonate rock. A rock, for example, limestone, calcite, and 

dolomite, that consist primarily of carbonate minerals.

cement (sedimentary). Mineral material, usually chemically 

precipitated, that occurs in the spaces among the 

individual grains of a sedimentary rock, thus binding the 

grains together.

cementation. The process by which clastic sediments 

become lithified or consolidated into hard, compact 

rocks, usually through deposition or precipitation of 

minerals in the spaces among the individual grains of the 

sediment; may occur simultaneously with sedimentation 

or at a later time.

cephalopod. A marine mollusk of the class Cephalopoda, 

characterized by a head surrounded by tentacles and, in 

most fossil forms, a straight, curved, or coiled calcareous 

shell divided into chambers. Range: Cambrian to 

Holocene. 

channel. The bed where a natural body of surface water 

flows or may flow. Also, a natural passageway or 

depression of perceptible extent containing continuously 

or periodically flowing water, or forming a connecting link 

between two bodies of water.

chemical weathering. Chemical breakdown of minerals at 

Earth’s surface via reaction with water, air, or dissolved 

substances; commonly results in a change in chemical 

composition providing more stablity in the current 

environment.

chronology. The arrangement of events in their proper 

sequence in time.

clast. An individual constituent, grain, or fragment of a rock 

or unconsolidated deposit, produced by the mechanical 

or chemical disintegration of a larger rock mass.

clastic. Describes rocks or sediments made of fragments of 

preexisting rocks.

clay. Minerals and sedimentary fragments that are less than 

1/256 mm (0.00015 in) across.

clay mineral. Any mineral occurring in the clay-sized 

fraction with the understanding that size imposes physical 

and chemical characteristics. 

claystone (sedimentary). An indurated rock with more than 

67% clay-sized minerals.

coarse-grained. Describes a crystalline rock and texture 

in which the individual minerals are relatively large, 

specifically an igneous rock whose particles have an 

average diameter greater than 5 mm (0.2 in). Also, 

describes sediment or sedimentary rock and texture in 

which the individual constituents are easily seen with the 

unaided eye, specifically sediment or rock whose particles 

have an average diameter greater than 2 mm (0.08 in).

coastal plain. Any lowland area bordering a sea or ocean, 

extending inland to the nearest elevated land, and sloping 

very gently seaward; may result from the accumulation of 

material along a coast.

colluvium. A loose, heterogeneous, and incoherent mass 

of rock fragments and soil material deposited via surface 

runoff or slow continuous downslope creep; usually 

collects at the base of a slope or hillside, but includes 

loose material covering hillsides.

compaction. The process whereby fine-grained sediment is 

converted to consolidated rock.

compression. A decrease in volume of material (including 

Earth’s crust) as it is pressed or squeezed together.

confined aquifer. An aquifer bounded above and below 

by confining beds. An aquifer containing confined 

groundwater.

confined groundwater. Groundwater under pressure 

significantly greater than that of the atmosphere. Its upper 

surface is the bottom of a confining bed.

confining bed. A body of relatively impermeable or distinctly 

less permeable material stratigraphically adjacent to one 

or more aquifers. Replaced the term “aquiclude.”

conglomerate. A coarse-grained, generally unsorted, 

sedimentary rock consisting of cemented, rounded clasts 

larger than 2 mm (0.08 in) in diameter.

contact. The surface between two types or ages of rocks.

continental. Formed on land rather than in the sea. 

Continental deposits may be of lake, swamp, wind, 

stream, or volcanic origin.

continental drift. A term for the process by which continents 

move relative to one another; it is a consequence of plate 

tectonics.

continental crust. Earth’s crust that is rich in silica 

and aluminum and underlies the continents and the 

continental shelves; ranges in thickness from about 25 

km (15 mi) to more than 70 km (40 mi) under mountain 
61

ranges, averaging about 40 km (25 km) thick.

coprolite. Fossilized feces.

coquina. Limestone composed of cemented shell fragments. 

coral. Any of a large group of bottom-dwelling, sessile, 

marine invertebrate organisms (polyps) that belong to 

the class Anthozoa (phylum Cnidaria), characterized by 

production of an external skeletons of calcium carbonate; 

may exist as solitary individuals or grow in colonies. 

Range: Abundant in the fossil record in all periods later 

than the Cambrian.

core (drill). A cylindrical section of rock or sediment. usually 

5–10 cm (2–4 in) across and up to several meters long, 

taken as a sample of the interval penetrated by a core bit, 

and brought to the surface for geologic examination and/

or laboratory analysis.

creep. The slow, imperceptible downslope movement of 

mineral, rock, and soil particles under gravity.

cross-bed. A single bed, inclined at an angle to the main 

planes of stratification; the term is commonly restricted to 

a bed that is more than 1 cm (0.4 in) thick.

cross-bedding. Uniform to highly varied sets of inclined 

beds deposited by wind or water that indicate flow 

conditions such as direction and depth. 

cross section. A graphic interpretation of geology, structure, 

or stratigraphy based on mapped and measured geologic 

extents and attitudes, depicted in a vertical plane (i.e., a 

cut or profile view).

cross-stratification. Arrangement of strata inclined at an 

angle to the main stratification. This is a general term that 

is commonly divided into cross-bed, which is cross-strata 

thicker than 1 cm (0.4 in); and cross-lamination, which is 

cross-strata thinner than 1 cm (0.4 in).

crust. Earth’s outermost layer or shell. 

crystalline. Describes a regular, orderly, repeating geometric 

structural arrangement of atoms.

crystal structure. The orderly and repeated arrangement of 

atoms in a crystal.

cutbank. A steep, bare, slope formed by lateral erosion of a 

stream.

debris flow. A moving mass of rock fragments, soil, and 

mud, with more than half of the particles larger than sand 

size. Slow debris flows may move less that 1 m (3 ft) per 

year; rapid ones reach 160 kph (100 mph). 

deformation. The process of folding, faulting, shearing, or 

fabric development in rocks as a result of Earth stresses.

depocenter. An area or site of maximum deposition.

detritus. Loose rock and mineral material that is worn off or 

removed by mechanical processes.

differential erosion. Erosion that occurs at irregular or 

varying rates due to differences in the resistance and 

hardness of surface material: softer and weaker rocks 

are rapidly worn away; harder and more resistant rocks 

remain to form ridges, hills, or mountains.

dip. The angle between a bed or other geologic surface and 

the horizontal plane.

dip-slip fault. A fault with measurable offset where the 

relative movement is parallel to the dip of the fault. 

discharge. The rate of flow of surface water or groundwater 

at a given moment, expressed as volume per unit of time.

displacement. The relative movement of the two sides of a 

fault; also, the specific amount of such movement.

dolomite (mineral). A carbonate (carbon + oxygen) mineral 

of calcium and magnesium, CaMg(CO3

)2. 

dolomite (rock). A carbonate sedimentary rock containing 

more than 50% of the mineral dolomite (calciummagnesium carbonate).

dolomitic. Describes a rock containing dolomite, especially 

one that contains 5%–50% of the mineral dolomite in the 

form of cement and/or grains or crystals.

downcutting. Stream erosion in which cutting is directed 

primarily downward, as opposed to laterally.

drainage. The manner in which the waters of an area flow 

off in surface streams or subsurface conduits; also, the 

processes of surface drainage of water from an area by 

streamflow and sheet flow, and the removal of excess 

water from soil by downward flow.

drainage basin. A region or area bounded by a drainage 

divide and occupied by a drainage system, specifically 

the tract of country that gathers water originating as 

precipitation and contributes it to a particular stream 

channel or system of channels, or to a lake, reservoir, or 

other body of water.

dredge (engineering). A floating machine for excavating 

sedimentary material from the bottom of a body of water.

dredge (oceanography). An ocean-bottom sampler that 

scrapes material from the sea floor as the device is dragged 

behind a slowly moving ship. 

dune. A low mound or ridge of sediment, usually sand, 

deposited by the wind. 

entrenched meander. An incised meander carved 

downward into the surface of the valley in which the 

meander originally formed; preserves its original pattern 

with little modification, suggesting rejuvenation of a 

meandering stream as a result of rapid vertical uplift or a 

lowering of base level; exhibits a symmetric cross profile 

in a gorge or canyon setting.

entrenched stream. A stream, often meandering, that flows 

in a narrow canyon or valley (i.e., “trench”) cut into a 

plain or relatively level upland; specifically a stream that 

has inherited its course from a previous cycle of erosion 

and that cuts into bedrock with little modification of the 

original course. 

epicenter. The point on Earth’s surface directly above the 

initial rupture point of an earthquake.

erosion. The general process or group of processes that 

loosen, dissolve, wear away, and simultaneously move 

from one place to another, the materials of Earth’s crust; 

includes weathering, solution, abrasive actions, and 

transportation, but usually excludes slope movements.

escarpment. A steep cliff or topographic step resulting from 

vertical displacement on a fault or as a result of slope 

movement or erosion. Synonymous with “scarp.”

estuary. The seaward end or tidal mouth of a river where 

freshwater and seawater mix.

extension. Deformation of Earth’s crust whereby rocks are 

pulled apart. 
62

fabric. The complete spatial and geometrical configuration 

of all components that make up a deformed rock, 

including texture, structure, and preferred orientation.

facies (sedimentary). The depositional or environmental 

conditions reflected in the sedimentary structures, 

textures, mineralogy, fossils, and other components of a 

sedimentary rock.

fault. A break in rock characterized by displacement of one 

side relative to the other.

fine-grained. Describes sediment or sedimentary rock and 

texture in which the individual constituents are too small 

to distinguish with the unaided eye, specifically sediment 

or rock whose particles have an average diameter less 

than 1/16 mm (0.002 in), that is, silt-size particles and 

smaller. Also, describes a crystalline or glassy rock and 

texture in which the individual minerals are relatively 

small, specifically an igneous rock whose particles have an 

average diameter less than 1 mm (0.04 in). 

floodplain. The surface or strip of relatively smooth land 

composed of alluvium and adjacent to a river channel, 

constructed by the present river in its existing regimen 

and covered with water when the river overflows its 

banks. A river has one floodplain and may have one or 

more terraces representing abandoned floodplains.

fluvial. Of or pertaining to a river or rivers.

fluvial channel. A natural passageway or depression 

produced by the action of a stream or river. 

fold. A curve or bend in an originally flat structure, such 

as a rock stratum, bedding plane, or foliation; usually a 

product of deformation.

footwall. The lower wall of a fault. 

foraminifer. Any protozoan belonging to the subclass 

Sarcodina, order Foraminiferida, characterized by the 

presence of a test of one to many chambers composed 

of secreted calcite (rarely silica or aragonite) or of 

agglutinated particles; most foraminifers are marine 

but freshwater forms are known. Range: Cambrian to 

Holocene. 

formation. Fundamental rock-stratigraphic unit that is 

mappable, lithologically distinct from adjoining strata, 

and has definable upper and lower contacts.

fossil. A remain, trace, or imprint of a plant or animal that 

has been preserved in the Earth’s crust since some past 

geologic time; loosely, any evidence of past life.

fracture. The breaking of a mineral other than along planes 

of cleavage. Also, any break in a rock such as a crack, joint, 

or fault.

friable. Describes a rock or mineral that is easily crumbled. 

gastropod. Any mollusk belonging to the class Gastropoda, 

characterized by a distinct head with eyes and tentacles 

and, in most, by a single calcareous shell that is closed 

at the apex, sometimes spiraled, not chambered, and 

generally asymmetrical. Range: Upper Cambrian to 

Holocene. 

geodetic surveying. Surveying that takes into account 

the figure and size of Earth, with corrections made for 

curvature; used where the areas or distances involved are 

so great that the desired accuracy and precision cannot 

be obtained by plane (ordinary field and topographic) 

surveying.

geology. The study of Earth, including its origin, history, 

physical processes, components, and morphology.

geomorphology. The study of the general configuration of 

surface landforms and their relationships to underlying 

structures, and of the history of geologic changes as 

recorded by these surface features.

glauconite. A greenish silicate (silicon + oxygen) mineral, 

(K,Na)(Fe,Al,Mg)2

(Si,Al)4O10(OH)2, characterized 

by a micaceous structure, commonly interstratified 

with smectite; may serve as an indicator of very slow 

sedimentation. 

Gondwana. The late Paleozoic continent of the Southern 

Hemisphere and counterpart of Laurasia of the Northern 

Hemisphere; both were derived from the supercontinent 

Pangaea.

gradient. A degree of inclination (steepness of slope), or a 

rate of ascent or descent, of an inclined part of Earth’s 

surface with respect to the horizontal; expressed as a ratio 

(vertical to horizontal), a fraction (such as m/km or ft/

mi), a percentage (of horizontal distance), or an angle (in 

degrees).

graben. An elongated, downdropped trough or basin, 

bounded on both sides by high-angle normal faults that 

dip toward one another. 

gravel. An unconsolidated, natural accumulation of typically 

rounded rock fragments resulting from erosion; consists 

predominantly of particles larger than sand; that is, 

greater than 2 mm (1/12 in) across.

groundwater. That part of subsurface water that is in the 

zone of saturation, including underground streams.

groundwater basin. An area of bedrock in a karst spring 

that collects drainage from all the sinkholes and sinking 

streams in its drainage area.

gully. A small channel produced by running water in 

unconsolidated material.

hanging wall. The upper wall of a fault. 

heterogeneous. Consisting of dissimilar or diverse 

ingredients or constituents.

highstand. The interval of time during one or more cycles of 

relative sea level change when sea level is above the edge 

of the continental shelf in a given area. 

horst. An elongated, uplifted block that is bounded on both 

sides by normal faults that dip away from one another. 

hurricane. The term applied in the Northern Hemisphere 

for an atmospheric low-pressure system with a closed, 

roughly circular, wind motion that is counterclockwise, 

and sustained near-surface wind speed equal to or 

exceeding 64 knots (73 mph).

hydraulic conductivity. The ease with which water moves 

through spaces or pores in soil or rock.

hydrogeology. The science that deals with subsurface waters 

and related geologic aspects of surface waters, including 

the movement of groundwater; the mechanical, chemical, 

and thermal interaction of groundwater with the porous 

medium; and the transport of energy and chemical 

constituents by the flow of groundwater. Synonymous 

with “geohydrology.” 

hydrology. The study of liquid and solid water properties, 

circulation, and distribution, on and under the Earth’s 
63

surface and in the atmosphere.

igneous. Describes a rock or mineral that solidified 

from molten or partly molten material; also, describes 

processes leading to, related to, or resulting from the 

formation of such rocks. One of the three main classes or 

rocks—igneous, metamorphic, and sedimentary.

incised meander. An old stream meander that has become 

deepened by rejuvenation and that is more or less closely 

bordered or enclosed by valley walls. The term is used 

collectively and includes “entrenched meanders” and 

“ingrown meanders.”

incision. Downward erosion by a stream, resulting in a 

deepened channel and commonly a narrow, steep-walled 

valley.

indurated. Describes a rock or soil hardened or 

consolidated by pressure, cementation, or heat.

ingrown meander. A continually growing or expanding 

incised meander formed during a single cycle of erosion 

by the enlargement of an initial minor meander while the 

stream was actively downcutting; exhibits a pronounced 

asymmetric cross profile (a well-developed, steep 

undercut slope on the outside of the meander, a gentle 

slip-off slope on the inside) and is produced when the rate 

of downcutting is slow enough to afford time for lateral 

erosion.

interfluve. The area between rivers, especially the relatively 

undissected upland or ridge between two adjacent valleys 

containing streams flowing in the same general direction.

joint. A break in rock without relative movement of rocks on 

either side of the fracture surface.

karstification. The action of water, mainly solutional but also 

mechanical, that produces features of karst topography.

karst. A type of topography that is formed on limestone, 

gypsum, and other soluble rocks, primarily by dissolution. 

It is characterized by sinkholes, caves, and underground 

drainage.

lacustrine. Describes a process, feature, or organism 

pertaining to, produced by, or inhabiting a lake.

lagoon. A narrow body of water that is parallel to the 

shore and between the mainland and a barrier island; 

characterized by minimal or no freshwater influx and 

limited tidal flux, which cause elevated salinities. Also, a 

shallow body of water enclosed or nearly enclosed within 

an atoll.

landslide. A collective term covering a wide variety of 

slope-movement landforms and processes that involve the 

downslope transport of soil and rock material en masse 

under the influence of gravity.

Laurasia. The late Paleozoic continent of the Northern 

Hemisphere and counterpart of Gonwana of the Southern 

Hemisphere; both were derived from the supercontinent 

Pangaea.

left-lateral fault. A strike-slip fault on which the side 

opposite the observer has been displaced to the left. 

Synonymous with “sinistral fault.”

lens. A sedimentary deposit that resembles a convex lens 

and is characterized by converging surfaces, thick in the 

middle and thinning out toward the edges.

levee. A long broad low embankment of sand and coarse silt 

built by floodwater overflow along both banks of a stream 

channel.

light detection and ranging/LiDAR. A method and 

instrument that measures distance to a reflecting object 

by emitting timed pulses of light and measuring the time 

between emission and reception of reflected pulses; the 

measured interval is converted to distance. 

lime. Calcium oxide, CaO.

limestone. A carbonate sedimentary rock consisting of more 

than 95% calcite and less than 5% dolomite.

liquefaction. The transformation of loosely packed sediment 

into a more tightly packed fluid mass.

lithosphere. Earth’s relatively rigid outer shell that consists 

of the entire crust plus the uppermost mantle. It is broken 

into about 20 plates, and according to the theory of plate 

tectonics, movement and interaction of these plates is 

responsible for most geologic activity.

lunar tide. The part of the tide caused solely by the tideproducing force of the Moon.

mantle. The zone of the Earth below the crust and above the 

core.

marl. A term loosely applied to a variety of materials, most of 

which occur as loose, earthy deposits consisting primarily 

of a mixture of clay and calcium carbonate; specifically an 

earthy substance containing 35%–65% clay and 65%–

35% carbonate.

marlstone. A sedimentary rock composed of marl.

mass wasting. Dislodgement and downslope transport of 

a mass of rock and/or unconsolidated material under 

the direct influence of gravity. In contrast to “erosion,” 

the debris removed is not carried within, on, or under 

another medium. Synonymous with “slope movement.”

matrix. The fine-grained material between coarse grains in 

an igneous or sedimentary rock. Also refers to rock or 

sediment in which a fossil is embedded.

meander. One of a series of sinuous curves, bends, or turns 

in the course of a stream, produced by a mature stream 

swinging from side to side as it flows across its floodplain 

or shifts its course laterally toward the convex side of an 

original curve.

mechanical weathering. The physical breakup of rocks 

without change in composition. 

medium-grained. Describes an igneous rock and texture in 

which the individual crystals have an average diameter 

in the range of 1 to 5 mm (0.04 to 0.2 in.). Also, describes 

sediment or sedimentary rock and texture in which the 

individual particles have an average diameter in the range 

of 1/16 to 2 mm (0.002 to 0.08 in), that is, sand size.

megabreccia. A rock produced by brecciation on a very large 

scale; individual blocks are as much as 400 m (1,300 ft) 

long.

member. A lithostratigraphic unit with definable contacts; a 

subdivision of a formation.

metamorphic rock. Any rock derived from preexisting 

rocks that was altered in response to marked changes 

in temperature, pressure, shearing stress, and chemical 

environment. One of the three main classes of rock—

igneous, metamorphic, and sedimentary.
64

meteoric water. Water of recent atmospheric origin.

mineral. A naturally occurring inorganic crystalline solid 

with a definite chemical composition or compositional 

range.

mollusk. A solitary invertebrate such as gastropods, bivalves, 

and cephalopods belonging to the phylum Mollusca. 

Range: Lower Cambrian to Holocene. 

normal fault. A fault in which the hanging wall appears to 

have moved downward relative to the footwall; the angle 

of dip is usually 45°–90°. 

oceanic crust. Earth’s crust that underlies the ocean basins 

and is rich in iron and magnesium; ranges in thickness 

from about 5 to 10 km (3 to 6 mi).

orogeny. A mountain-building event.

ostracode. Any aquatic crustacean belonging to the subclass 

Ostracoda, characterized by a two-valved (shelled), 

generally calcified carapace with a hinge along the dorsal 

margin. Range: Lower Cambrian to Holocene.

outcrop. Any part of a rock mass or formation that is 

exposed or “crops out” at Earth’s surface. 

oxide. A mineral group composed of oxygen plus an element 

or elements, for example, iron in hematite, Fe2

O3; or 

aluminum in corundum, Al2

O3.

paleogeography. The study, description, and reconstruction 

of the physical landscape in past geologic periods.

paleontology. The study of the life and chronology of 

Earth’s geologic past based on the fossil record.

Pangaea. A supercontinent that existed from about 300 

million to about 200 million years ago and included most 

of the continental crust of the Earth, from which the 

present continents were derived by fragmentation and 

continental drift. During an intermediate stage of the 

fragmentation—between the existence of Pangaea and 

that of the present continents—Pangaea split into two 

large fragments, Laurasia in the Northern Hemisphere 

and Gondwana in the Southern Hemisphere.

passive margin. A continental plate boundary where no 

plate-scale tectonism is taking place; plates are not 

converging, diverging, or sliding past one another.

peat. An accumulation of partly decomposed plant remains 

in swampy lowlands. It is an early stage or rank in the 

development of coal.

pebble. A small rounded rock, especially a waterworn stone, 

between 4 and 64 mm (0.16 and 2.5 in) across.

perched aquifer. An aquifer that is separated from 

(“perched” above) the water table by an unsaturated zone.

period. The fundamental unit of the worldwide geologic 

time scale. It is lower in rank than era and higher than 

epoch. The geochronologic unit during which the rocks of 

the corresponding system were formed.

permeability. A measure of the relative ease with which 

a fluid moves through the pore spaces of a rock or 

unconsolidated deposit.

phreatic. Of or relating to groundwater.

phreatic zone. The zone of saturation. 

pier. A platform extending over water from a shore that is 

supported by piles or pillars, used to secure, protect, and 

provide access to ships or boats.

piping. Erosion or solution by percolating water in a layer 

of subsoil, resulting in the formation of narrow conduits, 

tunnels, or “pipes” through which soluble or granular soil 

material is removed.

plate boundary. A zone of seismic and tectonic activity 

along the edges of lithospheric plates, resulting from the 

relative motion among plates. 

plate tectonics. A theory of global tectonics in which the 

lithosphere is divided into about 20 rigid plates that 

interact with one another at their boundaries, causing 

seismic and tectonic activity along these boundaries.

plateau. A broad, flat-topped topographic high (terrestrial 

or marine) of great extent and elevation above the 

surrounding plains, canyons, or valleys.

platform. Any level or nearly level surface.

point bar. A low ridge of sand and gravel deposited in a 

stream channel on the inside of a meander, where flow 

velocity slows.

porosity. The percentage of total void space in a volume of 

rock or unconsolidated deposit.

Precambrian. A commonly used term to designate all rocks 

older than the Cambrian Period of the Standard Global 

Chronostratigraphic Scale. It includes the Archean and 

Proterozoic eons and represents 90% of geologic time.

pull-apart basin. A topographic depression created by an 

extensional bend or extensional overstep along a strikeslip fault.

quartz. Silicon dioxide, SiO2. The only silicate (silicon + 

oxygen) mineral consisting entirely of silicon and oxygen. 

Synonymous with “crystalline silica.”

rebound. Upward flexing of Earth’s crust. Synonymous with 

“upwarping.”

recharge. The addition of water to the saturated zone below 

the water table.

reef. A ridgelike or moundlike structure, layered or massive, 

built by sedentary calcareous organisms (e.g., corals) and 

consisting mostly of their remains.

regolith. From the Greek “rhegos” (blanket) + “lithos” 

(stone), the layer of unconsolidated rock material that 

forms the surface of the land and overlies or covers 

bedrock; includes rock debris of all kinds, volcanic ash, 

glacial drift, alluvium, loess, and aeolian deposits, vegetal 

accumulations, and soil.

regression. Long-term seaward retreat of the shoreline or 

relative fall of sea level.

rejuvenation. The renewal of any geologic process.

reverse fault. A contractional high-angle (greater than 45°) 

dip-slip fault in which the hanging wall moves up relative 

to the footwall. 

revetment. A cover or facing of material placed directly on 

an existing slope, embankment or dike to protect the area 

from waves and strong currents. Revetments are designed 

to armor and protect the land behind them.

rift. A region of Earth’s crust where extension results in 

formation of many related normal faults, commonly 

associated with volcanic activity.
65

rift valley. A depression formed by grabens along the crest 

of a mid-ocean ridge or in a continental rift zone.

right-lateral fault. A strike-slip fault on which the side 

opposite the observer has been displaced to the right. 

ripple marks. The undulating, approximately parallel and 

usually small-scale pattern of ridges formed in sediment 

by the flow of wind or water.

riprap. A layer of large, durable rock fragments placed in an 

attempt to prevent erosion by water and thus preserve the 

shape of a surface, slope, or underlying structure.

rockfall. The most rapid type of slope movement in which a 

newly detached fragment of bedrock of any size falls from 

a cliff or other very steep slope, traveling straight down or 

in a series of leaps and bounds down a slope.

roundness. The relative amount of curvature of the 

“corners” of a sediment grain.

sand. A clastic particle smaller than a granule and larger than 

a silt grain, with a diameter ranging from 1/16 to 2 mm 

(0.0025 to 0.08 in).

sandstone. Clastic sedimentary rock composed of 

predominantly sand-sized grains.

sapping. The natural process of erosion along the base of a 

saturated zone. A subsurface zone in which all the 

interstices are filled with water under pressure greater 

than that of the atmosphere; separated from the 

unsaturated zone (above) by the water table.

scarp. A steep cliff or topographic step resulting from 

displacement on a fault or as a result of slope movement 

or erosion. Synonymous with “escarpment.”

scour. The powerful and concentrated clearing and digging 

action of flowing water, air, or ice.

seawall. Vertical structures used to protect backshore 

areas from heavy wave action, and in lower wave energy 

environments, to separate land from water. They can be 

constructed using a range of materials including poured 

concrete, steel sheet pile, concrete blocks, gabions, 

sandbags, or timber cribs.

sediment. An eroded and deposited, unconsolidated 

accumulation of rock and mineral fragments.

sedimentary. Pertaining to or containing sediment. 

sedimentary rock. A rock resulting from the consolidation 

of loose sediment that has accumulated in layers; it may 

be “clastic,” consisting of mechanically formed fragments 

of older rock; “chemical,” formed by precipitation from 

solution; or “organic,” consisting of the remains of plants 

and animals. One of the three main classes of rock—

igneous, metamorphic, and sedimentary. 

sedimentation. The process of forming or accumulating 

sediment into layers, including the separation of rock 

particles from parent rock, the transportation of these 

particles to the site of deposition, the actual deposition or 

settling of the particles, the chemical and other changes 

occurring in the sediment, and the ultimate consolidation 

of the sediment into solid rock. 

seismic. Pertaining to an earthquake or Earth vibration, 

including those that are artificially induced.

seismicity. The phenomenon of movements in the Earth’s 

crust. Synonymous with “seismic activity.”

sequence. A succession of geologic events, processes, or 

rocks, arranged in chronologic order to show their relative 

position and age with respect to geologic history as a 

whole. Also, a rock-stratigraphic unit that is traceable 

over large areas and defined by sediment associated with a 

major sea level transgression–regression.

shale. A clastic sedimentary rock made of clay-sized 

particles and characterized by fissility.

shear. Deformation resulting from stresses that cause 

contiguous parts of a body to slide relatively to each other 

in a direction parallel to their plane of contact. 

sheet erosion. The removal of thin layers of surface material 

more or less evenly from an extensive area of gently 

sloping land by broad continuous sheets of running water, 

rather than by streams flowing in well-defined channels.

sheetflood. A broad expanse of moving, storm-borne water 

that spreads as a thin, continuous, relatively uniform 

film over a large area in an arid region and that is not 

concentrated into well-defined channels; its distance of 

flow is short and its duration is measured in minutes or 

hours, commonly occurring after a period of sudden and 

heavy rainfall.

sheet flow. The downslope movement or overland 

flow of water, in the form of a thin, continuous film, 

over relatively smooth soil or rock surfaces and not 

concentrated into channels larger than rills.

sheetwash. A sheetflood occurring in a humid region. Also, 

the material transported and deposited by the water of a 

sheetwash. Used as a synonym of “sheet flow” and “sheet 

erosion.”

shoal. A relatively shallow place in a stream, lake, sea, or 

other body of water.

sill. Combination of elements from offshore breakwaters 

and rock revetments, typically built relatively close to 

shore, continuous and low-lying. Sills are generally built 

in lower wave energy regimes with the intent of reducing 

the wave climate and establishing marsh ecosystems or 

beaches.

silt. Clastic sedimentary material intermediate in size 

between fine-grained sand and coarse clay, 0.0039 to 

0.063 mm (0.00015 to 0.0025 in) across.

silting. The accumulation of silt suspended throughout a 

body of standing water or in some considerable portion 

of it. In particular, the choking, filling, or covering 

with stream-deposited silt behind a dam or other place 

of retarded flow, or in a reservoir. Synonymous with 

“siltation.”

siltstone. A clastic sedimentary rock composed of silt-sized 

grains.

sinkhole. A circular, commonly funnel-shaped depression in 

a karst area with subterranean drainage.

slope. The inclined surface of any part of Earth’s surface, 

such as a hillslope. Also, a broad part of a continent 

descending into an ocean.

slope movement. The gradual or rapid downslope 

movement of soil or rock under gravitational stress. 

Synonymous with “mass wasting.”

slope wash. Soil and rock material that is or has been 

transported down a slope under the force of gravity and 

assisted by running water not confined to channels; also, 
66

the process by which slope-wash material is moved.

slump. A generally large, coherent slope movement with a 

concave failure surface and subsequent backward rotation 

relative to the slope.

soil. The unconsolidated portion of the Earth’s crust 

modified through physical, chemical, and biotic processes 

into a medium capable of supporting plant growth.

solar tide. The part of the tide caused solely by the tideproducing force of the Sun.

sorted. Describes an unconsolidated sediment consisting of 

particles of essentially uniform size.

sorting. The dynamic process by which sedimentary 

particles having some particular characteristic (such as 

similarity of size, shape, or specific gravity) are naturally 

selected and separated from associated but dissimilar 

particles by the agents of transportation.

spalling. The process by which scales, plates, or flakes of 

rock, from less than a centimeter to several meters thick, 

successively fall from the bare surface of a large rock mass; 

a form of exfoliation.

spring. A place where groundwater flows naturally from a 

rock or the soil onto the land surface or into a body of 

surface water. 

storm surge. An abnormal, sudden rise of sea level along 

an open coast during a storm, caused primarily by strong 

winds offshore, or less frequently, a drop in atmospheric 

pressure, resulting in water piled up against the coast. It is 

most severe during high tide.

storm tide. The total observed seawater level during a storm, 

resulting from the combination of storm surge and the 

astronomical tide. An erroneous synonym of “storm 

surge.”

strata. Tabular or sheetlike layers of sedimentary rock 

that are visually distinctive from other layers above and 

below. The singular form of the term is stratum, but is less 

commonly used.

stratification. The accumulation or layering of sedimentary 

rocks as strata. Tabular, or planar, stratification refers to 

essentially parallel surfaces. Cross-stratification refers to 

strata inclined at an angle to the main stratification.

stratigraphic. Of or pertaining to strata.

stratigraphy. The geologic study of the origin, occurrence, 

distribution, classification, correlation, and age of rock 

layers, especially sedimentary rocks.

stream. Any body of water moving under gravity flow in a 

clearly confined channel.

stream channel. A long, narrow depression shaped by the 

concentrated flow of stream water.

stream terrace. A planar surface alongside a stream valley 

representing the remnants of an abandoned floodplain, 

stream bed, or valley floor produced during a former stage 

of erosion or deposition.

strike. The compass direction of the line of intersection of 

an inclined surface with a horizontal plane.

strike-slip fault. A fault with measurable offset where the 

relative movement is parallel to the strike of the fault. 

Described as left-lateral (sinistral) when relative motion of 

the block opposite the observer is to the left, and rightlateral (dextral) when relative motion is to the right. 

structural geology. The branch of geology that deals with 

the description, representation, and analysis of structures, 

primarily on a moderate to small scale. The subject is 

similar to tectonics, but the latter term is generally used 

for the analysis of broader regional or historical phases.

structure. The attitudes and relative positions of the rock 

masses of an area resulting from such processes as 

faulting, folding, and igneous intrusion.

subaerial. Describes a condition or process that exists or 

operates in the open air on or immediately adjacent to the 

land surface.

subaqueous. Describes conditions and processes, or 

features and deposits, that exist or are situated in or under 

water.

subsidence. The sudden sinking or gradual downward 

settling of part of Earth’s surface.

syncline. A generally concave upward fold of which the core 

contains the stratigraphically younger rocks. 

system (stratigraphy). The fundamental unit of 

chronostratigraphic classification of Phanerozoic rocks; 

each unit represents a time span and an episode of Earth 

history sufficiently great to serve as a worldwide reference 

unit. It is the temporal equivalent of a period. 

talus. Rock fragments, usually coarse and angular, lying at 

the base of a cliff or steep slope from which they have 

fallen.

tectonic. Describes a feature or process related to large-scale 

movement and deformation of Earth’s crust.

tectonics. The geologic study of the broad structural 

architecture and deformational processes of the 

lithosphere and asthenosphere.

terrace. Any long, narrow, relatively level or gently inclined 

surface (i.e., a bench or steplike ledge) that is bounded 

along one edge by a steeper descending slope and along 

the other edge by a steeper ascending slope, thus breaking 

the continuity of the slope; commonly occurs along the 

margin and above the level of a body of water, marking a 

former water level.

terrane. A fault-bounded body of rock of regional extent, 

characterized by a geologic history different from that of 

contiguous terranes or bounding continents.

terrestrial. Describes a feature, process, or organism related 

to land, Earth, or its inhabitants.

thalweg. The line connecting the lowest/deepest points 

along a stream bed; the line of maximum depth.

thrust fault. A dip-slip fault with a shallowly dipping (less 

than 45°) fault surface where the hanging wall moves up 

and over relative to the footwall. 

tombolo. A sand or gravel bar or barrier that connects an 

island with another landmass.

topography. The general morphology of Earth’s surface, 

including relief and locations of natural and human-made 

features.

trace (structural geology). The intersection of a geological 

surface with another surface, for example, the trace 

of bedding on a fault surface, or the trace of a fault or 

outcrop on the ground.
67

trace fossil. A fossilized feature such as a track, trail, 

burrow, or coprolite (dung), that preserves evidence of an 

organism’s life activities, rather than the organism itself. 

Compare to “body fossil.”

transform fault. A strike-slip fault that links two other faults 

or plate boundaries such as two segments of a mid-ocean 

ridge. 

transgression. Landward migration of the sea as a result of a 

relative rise in sea level.

trend. The direction or bearing of an outcrop of a geologic 

feature such as an ore body, fold, or orogenic belt.

type area. The geographic area or region that encompass 

the stratotype or type locality of a stratigraphic unit or 

stratigraphic boundary.

type locality. The place where a geologic feature such as an 

ore occurrence, a particular kind of igneous rock, or the 

type specimen of a fossil species was first recognized and 

described.

type section. The originally described sequence of strata 

that constitute a stratigraphic unit. It serves as an objective 

standard with which spatially separated parts of the unit 

may be compared, and it is preferably in an area where 

the unit shows maximum thickness and is completely 

exposed (or at least shows top and bottom).

unconfined groundwater. Groundwater that has a water 

table; water not confined under pressure beneath a 

confining bed.

unconformable. Describes strata that do not succeed the 

underlying rocks in immediate order of age or in parallel 

position, especially younger strata that do not have 

the same dip and strike as the underlying rocks. Also, 

describes the contact between unconformable rocks.

undercutting. The removal of material at the base of a steep 

slope by the erosive action of water (such as a meandering 

stream), sand-laden wind in a desert, or waves along a 

coast.

unsaturated zone. A subsurface zone between the land 

surface and the water table that includes air, gases, and 

water held by capillary action. Synonymous with “vadose 

zone” and “zone of aeration.”

uplift. A structurally high area in Earth’s crust produced by 

movement that raises the rocks.

upwarping. Upward flexing of Earth’s crust on a regional 

scale as a result of the removal of ice, water, sediments, or 

lava flows. 

vadose water. Water of the unsaturated zone.

volcanic. Pertaining to the activities, structures, or rock types 

of a volcano. A synonym of extrusive.

wash. A broad, gravelly, dry stream bed, generally in the 

bottom of a canyon that is periodically swept by a torrent 

of water. The term is used especially in the southwestern 

United States.

water table. The surface between the saturated zone and the 

unsaturated zone. Synonymous with “groundwater table” 

and “water level.”

weathering. The physical, chemical, and biological 

processes by which rock is broken down, particularly at 

Earth’s surface.

69

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Varnes, D. J. 1978. Slope movement types and processes. Pages 11–33 in R. L. Schuster and R. J. Krizek, editors. Landslides: analysis 

and control. Special Report 176. Transportation and Road Research Board, National Academy of Science, Washington, DC. 

Virginia Institute of Marine Science and National Park Service. 1994. Water resources management plan, Colonial National 

Historical Park. Internal planning document CA4000-1-0018. College of William and Mary, Gloucester Point, Virginia and 

Colonial National Historical Park, Yorktown, Virginia. 

Ward, L. W. 2008. Geology and paleontology of the James River; Richmond to Hampton Roads. Pages 1–25 in Guidebook Number 

7. Virginia Museum of Natural History, Martinsville, Virginia. 

Ward, L. W., and B. W. Blackwelder. 1975. Chesapecten, a new genus of Pectinidae (Mollusca: Bivalvia) from the Miocene and 

Pliocene of eastern North America. Professional Paper 861. U.S. Geological Survey, Washington, DC. http://pubs.er.usgs.gov/

publication/pp861 (accessed 2 October 2014).

Ward, L. W., and B. W. Blackwelder. 1980. Stratigraphic revision of upper Miocene and lower Pliocene beds of the Chesapeake 

Group, middle Atlantic Coastal Plain. Bulletin 1482-D. U.S. Geological Survey, Washington, DC. http://pubs.er.usgs.gov/

publication/b1482D (accessed 30 September 2014).
76

Waterways Experiment Station. 1951. Geology of the Lower Arkansas River alluvial valley, Pine Bluff, Arkansas, to mouth. Technical 

memorandum 3-332 conducted for the President, Mississippi River Commission, US Army Corps of Engineers, Vicksburg, 

Mississippi, USA. 

Whittecar, G. R. and D. F. Duffy. 2000. Geomorphology and stratigraphy of late Cenozoic alluvial fans, Augusta County, Virginia, 

USA. Pages 259–279 in G. M. Clark, H. H. Mills, and J. S. Kite, editors. Regolith in the Central and Southern Appalachians. 

Southeastern Geology 39(3-4).

Wieczorek, G. F. and J. B. Snyder. 2009. Monitoring slope movements. Pages 245–271 in R. Young and L. Norby, editors. Geological 

monitoring. Geological Society of America, Boulder, Colorado. http://go.nps.gov/monitor_slopes (accessed 26 September 2014).

Williams, M., A. M. Haywood, E. M. Harper, A. L. A. Johnson, T. Knowles, M. J. Leng, D. J. Lunt, B. Okamura, P. D. Taylor, and J. 

Zalasiewicz. 2009. Pliocene climate and seasonality in North Atlantic shelf seas. Philosophical Transactions of the Royal Society 

A: Mathematical, Physical and Engineering Sciences 367(1886):85–108.

Winkelstern, I., D. Surge, and J. W. Hudley. 2013. Multiproxy sclerochronological evidence for Plio-Pleistocene regional warmth: 

United States Mid-Atlantic Coastal Plain. Palaios 28(9):649–660.

Young, R. and L. Norby, editors. 2009. Geological monitoring. Geological Society of America, Boulder, Colorado.

http://go.nps.gov/geomonitoring (accessed 7 April 2015).

Zappi, P. A., M. R. Palermo, and M. W. LaSalle. 1990. Long-term management strategy for dredged material disposal for the Naval 

Weapons Station, Yorktown, Yorktown, Virginia; Naval Supply Center, Cheatham Annex, Williamsburg, Virginia; and Naval 

Amphibious Base, Little Creek, Norfolk, Virginia; Phase I: evaluation of existing management options and data. Miscellaneous 

Paper EL-90-8. US Army Engineer Waterways Experiment Station, Vicksburg, Mississippi.
77

Additional References

This chapter lists additional references, resources, and websites that may be of use to resource 

managers. Web addresses are valid as of May 2016. Refer to Appendix B for laws, regulations, and 

policies that apply to NPS geologic resources.

Geology of National Park Service Areas

● NPS Geologic Resources Division

Energy and Minerals; Active Processes and Hazards; 

Geologic Heritage:

http://go.nps.gov/geology

● NPS Geologic Resources Inventory:

http://go.nps.gov/gri

● NPS Geoscientist-In-the-Parks (GIP) internship 

and guest scientist program:

http://go.nps.gov/gip

● NPS Views program (geology-themed modules are 

available for Geologic Time, Paleontology, Glaciers, 

Caves and Karst, Coastal Geology, Volcanoes, and a 

variety of geologic parks):

http://www.nature.nps.gov/views/

● USGS Geology of National Parks (including 3D 

imagery): http://3dparks.wr.usgs.gov/

NPS Resource Management Guidance and 

Documents

● Management Policies 2006 (Chapter 4: Natural 

resource management):

http://www.nps.gov/policy/mp/policies.html

● 1998 National parks omnibus management act: 

https://www.gpo.gov/fdsys/pkg/PLAW-105publ391/

pdf/PLAW-105publ391.pdf

● NPS-75: Natural resource inventory and 

monitoring guideline:

http://www.nature.nps.gov/nps75/nps75.pdf

● NPS Natural resource management reference 

manual #77: http://www.nature.nps.gov/Rm77/

● Geologic monitoring manual (Young, R., and 

L. Norby, editors. 2009. Geological monitoring. 

Geological Society of America, Boulder, Colorado): 

http://go.nps.gov/geomonitoring

● NPS Technical Information Center (TIC) (Denver, 

Colorado; repository for technical documents): 

http://www.nps.gov/dsc/technicalinfocenter.htm

Climate Change Resources

● NPS Climate Change Response Program Resources: 

http://www.nps.gov/subjects/climatechange/

resources.htm

● US Global Change Research Program:

http://globalchange.gov/home

● Intergovernmental Panel on Climate Change:

http://www.ipcc.ch/

Geological Surveys and Societies

● Virginia Division of Geology and Mineral 

Resources: https://www.dmme.virginia.gov/dgmr/

divisiongeologymineralresources.shtml

● US Geological Survey: http://www.usgs.gov/

● Geological Society of America:

http://www.geosociety.org/

● American Geophysical Union: http://sites.agu.org/

● American Geosciences Institute:

http://www.americangeosciences.org/

● Association of American State Geologists:

http://www.stategeologists.org/

US Geological Survey Reference Tools

● National geologic map database (NGMDB):

http://ngmdb.usgs.gov/

● Geologic names lexicon (GEOLEX; geologic unit 

nomenclature and summary):

http://ngmdb.usgs.gov/Geolex/geolex_home.html

● Geographic names information system (GNIS; 

official listing of place names and geographic 

features): http://gnis.usgs.gov/

● GeoPDFs (download searchable PDFs of any 

topographic map in the United States):

http://store.usgs.gov (click on “Map Locator”)

● Publications warehouse (many publications 

available online): http://pubs.er.usgs.gov

● Tapestry of time and terrain (descriptions of 

physiographic provinces):

http://tapestry.usgs.gov/Default.html

79

Appendix A: Scoping Participants

The following people attended the GRI scoping meeting for Colonial National Historical Park, held on 

1 August 2005, or the follow-up report writing conference call, held on 12 November 2014. Discussions 

during these meetings supplied a foundation for this GRI report. The scoping summary document is 

available on the GRI publications website: http://go.nps.gov/gripubs.

2005 Scoping Meeting Participants

Name Affiliation Position

Rick Berquist Virginia Division of Mineral Resources Geologist

Mark Duffy NPS Northeast Coastal and Barrier Network

Dave Frederick NPS Colonial National Historical Park

Scott Hardaway Virginia Institute of Marine Science

Bruce Heise NPS Geologic Resources Division Geologist, GRI program coordinator

Matt Heller Virginia Division of Mineral Resources Geologist

Tom Nash NPS Colonial National Historical Park

Chuck Rafkind NPS Colonial National Historical Park Natural Resource Specialist

Melanie Ransmeier NPS Geologic Resources Division GIS Specialist

Karen Rehm NPS Colonial National Historical Park

Dan Smith NPS Colonial National Historical Park

Trista Thornberry-Ehrlich Colorado State University Geologist, Report author

2014 Conference Call Participants

Name Affiliation Position

Amanda Babson NPS Northeast Region Coastal climate adaptation coordinator

Rebecca Beavers NPS Geologic Resources Division Coastal geologist

Rick Berquist Virginia Division of Geology and Mineral Resources Geologist

Jim Comiskey NPS Northeast Region Program manager for Inventory & Monitoring

Jonathan Connelly NPS Colonial National Historical Park Cultural resources manager

Ken Doak NPS Colonial National Historical Park Chief ranger

David Frederick NPS Colonial National Historical Park GIS specialist

Dorothy Geyer NPS Colonial National Historical Park Natural resource specialist

Jason Kenworthy NPS Geologic Resources Division Geologist, GRI reports coordinator

Tim McLean NPS Colonial National Historical Park Civil engineer

Marcie Occhi Virginia Division of Geology and Mineral Resources Geologist

Cheryl Green NPS Colonial National Historical Park Administrator

Dan Smith NPS Colonial National Historical Park Superintendent

Sara Stevens NPS Northeast Coastal and Barrier Network Program manager

Trista Thornberry-Ehrlich Colorado State University Geologist, Author, Graphic designer

Steven Williams NPS Colonial National Historical Park Deputy superintendent

81

Appendix B: Geologic Resource Laws, Regulations, and Policies

The NPS Geologic Resources Division developed this table to summarize laws, regulations, and policies 

that specifically apply to National Park Service minerals and geologic resources. The table does not 

include laws of general application (e.g., Endangered Species Act, Clean Water Act, Wilderness Act, 

National Environmental Policy Act, or National Historic Preservation Act). The table does include the 

NPS Organic Act when it serves as the main authority for protection of a particular resource or when 

other, more specific laws are not available. Information is current as of May 2016. Contact the NPS 

Geologic Resources Division for detailed guidance.

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Paleontology

National Parks Omnibus Management 

Act of 1998, 16 USC § 5937 protects the 

confidentiality of the nature and specific 

location of paleontological resources and 

objects.

Paleontological Resources Preservation 

Act of 2009, 16 USC § 470aaa et 

seq. provides for the management and 

protection of paleontological resources on 

federal lands.

36 CFR § 2.1(a)(1)(iii) prohibits destroying, 

injuring, defacing, removing, digging or 

disturbing paleontological specimens or 

parts thereof.

Prohibition in 36 CFR § 13.35 applies 

even in Alaska parks, where the surface 

collection of other geologic resources is 

permitted.

Regulations in association with 2009 PRPA 

are being finalized (August 2015).

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity.

Section 4.8.2.1 emphasizes Inventory and 

Monitoring, encourages scientific research, 

directs parks to maintain confidentiality of 

paleontological information, and allows 

parks to buy fossils only in accordance with 

certain criteria.

Rocks and Minerals

NPS Organic Act, 16 USC § 1 et seq.

directs the NPS to conserve all resources 

in parks (including rock and mineral 

resources), unless otherwise authorized by 

law.

36 CFR § 2.1 prohibits possessing, 

destroying, disturbing mineral resources...

in park units.

Exception: 36 CFR § 13.35 allows some 

surface collection of rocks and minerals 

in some Alaska parks (not Klondike 

Gold Rush, Sitka, Denali, Glacier Bay, 

or Katmai) by non-disturbing methods 

(e.g., no pickaxes), which can be stopped 

by superintendent if collection causes 

significant adverse effects on park 

resources and visitor enjoyment.

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity.

Park Use of Sand and Gravel

Materials Act of 1947, 30 USC § 601

does not authorize the NPS to dispose of 

mineral materials outside of park units.

None applicable.

Section 9.1.3.3 clarifies that only the 

NPS or its agent can extract park-owned 

common variety minerals (e.g., sand and 

gravel), and:

-only for park administrative uses;

-after compliance with NEPA and other 

federal, state, and local laws, and a 

finding of non-impairment;

-after finding the use is park’s most 

reasonable alternative based on 

environment and economics;

-parks should use existing pits and create 

new pits only in accordance with parkwide borrow management plan;

-spoil areas must comply with Part 6 

standards; and

-NPS must evaluate use of external 

quarries.

Any deviation from this policy requires a 

written waiver from the Secretary, Assistant 

Secretary, or Director.
82

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Upland and Fluvial Processes

Rivers and Harbors Appropriation 

Act of 1899, 33 USC § 403 prohibits the 

construction of any obstruction on the 

waters of the United States not authorized 

by congress or approved by the USACE.

Clean Water Act 33 USC § 1342 requires 

a permit from the USACE prior to any 

discharge of dredged or fill material 

into navigable waters (waters of the US 

[including streams]). 

Executive Order 11988 requires federal 

agencies to avoid adverse impacts to 

floodplains. (see also D.O. 77-2)

Executive Order 11990 requires plans for 

potentially affected wetlands (including 

riparian wetlands). (see also D.O. 77-1)

None applicable.

Section 4.1 requires NPS to manage 

natural resources to preserve fundamental 

physical and biological processes, as well 

as individual species, features, and plant 

and animal communities; maintain all 

components and processes of naturally 

evolving park ecosystems.

Section 4.1.5 directs the NPS to reestablish natural functions and processes 

in human-disturbed components of natural 

systems in parks, unless directed otherwise 

by Congress.

Section 4.4.2.4 directs the NPS to allow 

natural recovery of landscapes disturbed by 

natural phenomena, unless manipulation of 

the landscape is necessary to protect park 

development or human safety. 

Section 4.6.4 directs the NPS to (1) 

manage for the preservation of floodplain 

values; [and] (2) minimize potentially 

hazardous conditions associated with 

flooding.

Section 4.6.6 directs the NPS to manage 

watersheds as complete hydrologic systems 

and minimize human-caused disturbance 

to the natural upland processes that deliver 

water, sediment, and woody debris to 

streams.

Section 4.8.1 directs the NPS to allow 

natural geologic processes to proceed 

unimpeded. Geologic processes...include...

erosion and sedimentation...processes. 

Section 4.8.2 directs the NPS to protect 

geologic features from the unacceptable 

impacts of human activity while allowing 

natural processes to continue.

Caves and Karst Systems

Federal Cave Resources Protection Act 

of 1988, 16 USC §§ 4301 – 4309 requires 

Interior/Agriculture to identify “significant 

caves” on Federal lands, regulate/

restrict use of those caves as appropriate, 

and include significant caves in land 

management planning efforts. Imposes 

civil and criminal penalties for harming 

a cave or cave resources. Authorizes 

Secretaries to withhold information about 

specific location of a significant cave from 

a Freedom of Information Act (FOIA) 

requester. 

National Parks Omnibus Management 

Act of 1998, 16 USC § 5937 protects the 

confidentiality of the nature and specific 

location of cave and karst resources.

36 CFR § 2.1 prohibits possessing/ 

destroying/disturbing...cave resources...in 

park units.

43 CFR Part 37 states that all NPS caves 

are “significant” and sets forth procedures 

for determining/releasing confidential 

information about specific cave locations to 

a FOIA requester.

Section 4.8.1.2 requires NPS to maintain 

karst integrity, minimize impacts.

Section 4.8.2 requires NPS to protect 

geologic features from adverse effects of 

human activity.

Section 4.8.2.2 requires NPS to protect 

caves, allow new development in or on 

caves if it will not impact cave environment, 

and to remove existing developments if 

they impair caves.

Section 6.3.11.2 explains how to manage 

caves in/adjacent to wilderness.
83

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Soils

Soil and Water Resources Conservation 

Act, 16 USC §§ 2011–2009 provides for 

the collection and analysis of soil and 

related resource data and the appraisal of 

the status, condition, and trends for these 

resources.

Farmland Protection Policy Act, 7 USC 

§ 4201 et. seq. requires NPS to identify 

and take into account the adverse effects 

of Federal programs on the preservation 

of farmland; consider alternative actions, 

and assure that such Federal programs 

are compatible with State, unit of local 

government, and private programs 

and policies to protect farmland. NPS 

actions are subject to the FPPA if they 

may irreversibly convert farmland (directly 

or indirectly) to nonagricultural use and 

are completed by a Federal agency or 

with assistance from a Federal agency. 

Applicable projects require coordination 

with the Department of Agriculture’s 

Natural Resources Conservation Service 

(NRCS).

7 CFR Parts 610 and 611 are the US 

Department of Agriculture regulations 

for the Natural Resources Conservation 

Service. Part 610 governs the NRCS 

technical assistance program, soil erosion 

predictions, and the conservation of private 

grazing land. Part 611 governs soil surveys 

and cartographic operations. The NRCS 

works with the NPS through cooperative 

arrangements.

Section 4.8.2.4 requires NPS to

-prevent unnatural erosion, removal, and 

contamination;

-conduct soil surveys;

-minimize unavoidable excavation; and

-develop/follow written prescriptions 

(instructions).

Coastal Features and Processes

NPS Organic Act, 16 USC § 1 et. 

seq. authorizes the NPS to promulgate 

regulations to protect park resources and 

values (from, for example, the exercise of 

mining and mineral rights).

Coastal Zone Management Act, 16 USC 

§ 1451 et. seq. requires Federal agencies 

to prepare a consistency determination for 

every Federal agency activity in or outside 

of the coastal zone that affects land or 

water use of the coastal zone.

Clean Water Act, 33 USC § 1342/Rivers 

and Harbors Act, 33 USC 403 require that 

dredge and fill actions comply with a Corps 

of Engineers Section 404 permit.

Executive Order 13089 (coral reefs) 

(1998) calls for reduction of impacts to 

coral reefs.

Executive Order 13158 (marine 

protected areas) (2000) requires every 

federal agency, to the extent permitted by 

law and the maximum extent practicable, 

to avoid harming marine protected areas.

36 CFR § 1.2(a)(3) applies NPS regulations 

to activities occurring within waters subject 

to the jurisdiction of the US located 

within the boundaries of a unit, including 

navigable water and areas within their 

ordinary reach, below the mean high water 

mark (or OHW line) without regard to 

ownership of submerged lands, tidelands, 

or lowlands.

36 CFR § 5.7 requires NPS authorization 

prior to constructing a building or other 

structure (including boat docks) upon, 

across, over, through, or under any park 

area.

Section 4.1.5 directs the NPS to reestablish natural functions and processes 

in human-disturbed components of natural 

systems in parks unless directed otherwise 

by Congress.

Section 4.4.2.4 directs the NPS to allow 

natural recovery of landscapes disturbed by 

natural phenomena, unless manipulation of 

the landscape is necessary to protect park 

development or human safety.

Section 4.8.1 requires NPS to allow natural 

geologic processes to proceed unimpeded. 

NPS can intervene in these processes 

only when required by Congress, when 

necessary for saving human lives, or when 

there is no other feasible way to protect 

other natural resources/ park facilities/

historic properties.

Section 4.8.1.1 requires NPS to:

-Allow natural processes to continue 

without interference,

-Investigate alternatives for mitigating the 

effects of human alterations of natural 

processes and restoring natural conditions, 

-Study impacts of cultural resource 

protection proposals on natural resources, 

-Use the most effective and natural-looking 

erosion control methods available, and 

-Avoid putting new developments in areas 

subject to natural shoreline processes 

unless certain factors are present.
84

Resource Resource-specific Laws Resource-specific Regulations 2006 Management Policies Climate Change

Secretarial Order 3289 (Addressing 

the Impacts of Climate Change on 

America’s Water, Land, and Other Natural 

and Cultural Resources) (2009) requires 

DOI bureaus and offices to incorporate 

climate change impacts into long-range 

planning; and establishes DOI regional 

climate change response centers and 

Landscape Conservation Cooperatives to 

better integrate science and management 

to address climate change and other 

landscape scale issues.

Executive Order 13653 (Preparing the 

United States for the Impacts of Climate 

Change) (2013) outlines Federal agency 

responsibilities in the areas of supporting 

climate resilient investment; managing 

lands and waters for climate preparedness 

and resilience; providing information, data 

and tools for climate change preparedness 

and resilience; and planning.

Executive Order 13693 (Planning for 

Federal Sustainability in the Next Decade) 

(2015) established to maintain Federal 

leadership in sustainability and greenhouse 

gas emission reductions.

President’s Climate Action Plan (2013), 

http://www.whitehouse.gov/sites/default/

files/image/president27sclimateactionplan.

pdf 

None applicable.

Section 4.1 requires NPS to investigate 

the possibility to restore natural ecosystem 

functioning that has been disrupted by past 

or ongoing human activities. This would 

include climate change, as put forth by 

Beavers et al. (in review).

NPS Climate Change Response Strategy

(2010) describes goals and objectives to 

guide NPS actions under four integrated 

components: science, adaptation, 

mitigation, and communication.

Policy Memo 12-02 (Applying National 

Park Service Management Policies in the 

Context of Climate Change) (2012) applies 

considerations of climate change to the 

impairment prohibition and to maintaining 

“natural conditions”.

Policy Memo 14-02 (Climate Change and 

Stewardship of Cultural Resources) (2014) 

provides guidance and direction regarding 

the stewardship of cultural resources in 

relation to climate change.

Policy Memo 15-01 (Climate Change 

and Natural Hazards for Facilities) (2015) 

provides guidance on the design of facilities 

to incorporate impacts of climate change 

adaptation and natural hazards when 

making decisions in national parks.

DOI Manual Part 523,

Chapter 1 establishes policy and provides 

guidance for addressing climate change 

impacts upon the Department’s mission, 

programs, operations, and personnel.

Revisiting Leopold: Resource 

Stewardship in the National Parks

(2012) will guide US National Park natural 

and cultural resource management into 

a second century of continuous change, 

including climate change.

Climate Change Action Plan (2012) 

articulates a set of high-priority no-regrets 

actions the NPS will undertake over the 

next few years

Green Parks Plan (2013) is a long-term 

strategic plan for sustainable management 

of NPS operations.
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 333/133343, June 2016
Natural Resource Stewardship and Science 

1201 Oak Ridge Drive, Suite 150 

Fort Collins, Colorado 80525

www.nature.nps.gov

National Park Service

U.S. Department of the Interior

EXPERIENCE YOUR AMERICATM
Plate 1. Maps of Colonial National Historical Park.

National Park Service maps, available at

https://www.nps.gov/hfc/cfm/carto.cfm(accessed 28 June 2016).
Qsnd 

Qom 

,.,.,!"'"-~ 1 Point 

Auodation 1-r the 

v119rz•~•:£:: 

HJ,STOR/C 

JAMESTOWN 

I 

NPS Boundary 

D 

• point of interest 

-- highways 

lmpad Strudure Lines 

------ outer rim of impact structure. inferred 

Faults 

•••••• normal fault contact (not exposed at surface), inferred 

---· unknown offset/d6placement fault, approximate 

•••••• unknown offset/d6placement fault, inferred 

__ _,_ __ unknown offset/d6placement fault, queried and inferred 

Geologic Units 

- wa ter 

Of Fill (Recent) 

Qms Marsh sediment (Recent) 

Qss Swamp sediment (Recent) 

Ob Beach and dune (Recent) 

Shelly organic mud (Recent) 


Oysters (Recent) 


Peat (Recent) 


Organic mud (Recent) 


Qsnd Sand (Recent) 

Qom 

Qom 

Qsg Sand and gravel (Recent) 

Qal Alluvium (Recent) 

Qt Tabb Allofo rmation, undivided (late Ple6tocene) 

Qtp Tabb Allofo rmation, Poquoson Member (late Pleistocene) 

Tabb Allofo rmation, Lynnhaven and Poquoson Members, undivided Qtlp (late Ple6tocene) 

Qtl Tabb Alloformation. Lynnhaven Member (late Pleistocene) 

Qts Tabb Alloformation, Sedgefield Member (late Pleistocene) 

Qeg E~ing Green Alloformation (late Pleistocene) 

Qsh Shirley Alloformation (middle Pleistocene) 

Qc Chuckatuck Alloformation (middle (?) Pleistocene) 

Qcc Charles City Alloformat,on (early Pleistocene) 


Qw Windsor Formation (early Pleistocene) 


Qm Moorings Unit of Oaks and Coch (1973) (early Pleistocene) 


Qbc Bacons Castle Formation (early Pleistocene) 


Cold Harbor Formation (late Pliocene) 


Yorktown Formation, Moore House Member (late Pliocene) 


Chesapeake Group, Yorlctovvn and Eastover Formations, undivided 


(Pliocene and early Pliocene) 


Qom / 

I 

\ 

Qsnd 

Swanns 

Point 

\ 

;r ..,, I~ 

,,-Tc "?~ I 

Qbc ~SI 

I ~/,.,,E'~ 

I Qsnd I Qom Qsh 

I 2 

Kilometers 

Full Extent of GRI GIS Data; M ap Extents in Red 

CHESAPEAKE 

BAY 

'I..WPORT NfW~ 

• o I 

HAMfJ' 

This map was produced by Georgia Hybels (Colorado State Univers~y) in June 20 16. It is an 

overview of compiled geologic data prepared as part of the NPS Geologic Resources 

Inventory. Th 6 map 6 not a substitute for s~e-specific investigations. 

The source map used in creation of the dig~al geologic data was: 

Berquist, C. R., Jr. 201 5. Geologic Map of the Williamsburg 30- x 60-minute Quadrangle, 

Virginia (scale 1 :100,000). Unpubl6hed. Virginia Division of Geology and Mineral 

Resources, Charlottesville.Virginia. 

As per source map scale and U.S. National Map Accuracy Standards, geologic features 

represented here are expected to be within 51 m (167 ft) of theirtrue location. 

All digital geologic data and publications prepared as part of the Geologic Resources 

Inventory are available at the NPS Integrated Resource Management Applications Portal 

(IRMA): https://irma.nps.gov/App/Reference/Search. Enter "GRI " as the search text and 

select a park from the unit 161. 
Colonial National Historical Park Map Unit Properties Table, Page 1 of 6 

Map Unit Properties Table: Colonial National Historical Park 

Gray-shaded map units are not mapped within Colonial National Historical Park. Bold text refers to sections in report. 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY 

(Recent) 

Fill

(Qf) 

Unit Qf consists of unsorted, jumbled, undifferentiated 

material such as sand or gravel used for fill. Modified or 

disturbed earth materials also fall into this unit type.

Qf is mapped at Jamestown Island, Yorktown, and along the 

Colonial Parkway.

None documented

Shoreline Erosion, Sediment Transport, and Coastal 

Engineering Structures—this unit composes many of the 

coastal engineering structures along the James and York 

rivers in place to protect reaches of the shoreline. 

Building and Reshaping the Coastal Plain—unit Qf

reflects human attempts to reshape the landscape and 

resist changes brought about by Earth surface processes 

such as shoreline erosion and flooding.

Marsh sediment

(Qms) 

Qms accumulates in marshes, bogs, and wetland areas. Qms

is rich in organic deposits such as plant debris and includes 

fine sand and clay interlayers. 

Qms occurs at Swanns Point, Jamestown Island, Yorktown, 

and along the Colonial Parkway.

Paleontological Resources—Qms contains organic 

material that may include plant debris and fossil pollen. 

Foraminifera, spores, conifer and angiosperm pollen, and 

pine and angiosperm phytoliths on occur on Jamestown 

Island, dating from about 37,000 years ago to the present. 

On the York River, Qms may contain late Pleistocene 

bivalves and gastropods and potentially host mastodon 

remains.

Hydrogeologic System at Yorktown Battlefield—Qms

may be part of the interlayered shallow system of aquifers 

and confining layers. Sandy sediments are part of the 

Columbia and Cornwallis Cave aquifers. Clay-rich layers 

are part of the Cornwallis Cave confining unit.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Groundwater Quantity and Quality—this unit is part of 

the regional shallow aquifer and confining layer system at 

Yorktown Battlefield.

Building and Reshaping the Coastal Plain—these are 

among the youngest geologic map units occurring on the 

landscape at Colonial National Historical Park. These units 

reflect the ongoing processes of deposition of sediments 

weathered from the highlands and fluvial and other earth 

surface processes acting on the sediments that compose 

the Coastal Plain.

Qms and Qss formed in estuarine, marsh, and swamp 

environments.

Qb formed in beach and shoreline environments.

Qshom and Qoy may be Pleistocene in age.

Swamp sediment

(Qss)

Qss accumulates in swamps and other still-water areas. Qss is 

rich in organic deposits such as peat and includes silt, fine 

sand, and clay interlayers.

Qss is mapped at Swanns Point and along the Colonial 

Parkway.

Paleontological Resources—Qss contains organic 

material that may include plant debris and fossil pollen.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Beach and dune

(Qb)

Qb consists of fine- to coarse-grained quartz sand. The sand is 

poorly to well-sorted. As mapped, this unit may include 

shoreline stabilizing riprap adjacent to water.

Qb occurs at Jamestown Island and may have been used for 

iron casting.

None documented None documented

Shelly organic mud

(Qshom) 

Qshom contains organic mud with abundant fossil and 

modern shells, fragments of shells, and some interbedded 

sand. Most of this unit is exposed at the shoreline or under 

water. 

Fluvial Features and Processes—Qshom is mapped 

submerged beneath the James River near Jamestown 

Island and along the York River bottom and may be a sand 

resource. 

Paleontological Resources—Qshom contains fossil 

shells and shell debris. Shell types include oyster, Rangia, 

and other shells. 

Shoreline Erosion, Sediment Transport, and Coastal 

Engineering Structures—these units are among the 

bottom-sediment units mapped in the James and York 

rivers. These sediments are constantly in flux in the 

channel and may be dredged periodically. 

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan. Oysters

(Qoy)

Qoy contains live oysters and oyster shells in a sandy or 

muddy substrate. Qoy may form reef-like forms. Qoy is part 

of the submerged bottom sediment mapping. 

Paleontological Resources—Qoy contains oyster shells 

and shell debris.
Gray-shaded map units are not mapped within Colonial National Historical Park. Bold text refers to sections in report.

Colonial National Historical Park Map Unit Properties Table, Page 2 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY 

(Recent) 

Peat

(Qpe)

Qpe consists of decomposed plant remains commonly mixed 

with sand or mud. 

Paleontological Resources—Qpe contains fossil shells 

roots of inundated marsh and swamp plants. Shoreline Erosion, Sediment Transport, and Coastal 

Engineering Structures—these unitsare among the 

bottom-sediment units mapped in the James and York 

rivers. These sediments are constantly in flux in the 

channel and may be dredged periodically.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Building and Reshaping the Coastal Plain—these are

among the youngest geologic map units occurring on the 

landscape at Colonial National Historical Park. These units 

reflect the ongoing processes of deposition of sediments 

weathered from the highlands and fluvial and other earth 

surface processes acting on the sediments which compose 

the Coastal Plain.

Qpe may be Pleistocene in age.

Qom formed in estuarine, marsh, and swamp 

environments.

Qsnd formed in beach and shoreline environments. 

Qsg and Qal formed in fluvial environments as channels 

incised through Coastal-Plain sediments.

Organic mud

(Qom)

Qom consists of black, dark gray or dark brown clay and silt. 

Organic material is abundant. 

Qom is mapped at Jamestown Island.

Fluvial Features and Processes—Qbs is mapped 

submerged beneath the James River near Jamestown 

Island. 

Paleontological Resources—Qom contains organic 

material that may include plant debris and fossil pollen. 

Foraminifera, spores, conifer and angiosperm pollen, and 

pine and angiosperm phytoliths occur on Jamestown 

Island, dating from about 37,000 years ago to the present.

Sand

(Qsnd) 

Qsnd is fine- to coarse-grained, poorly to well-sorted quartz 

sand similar to Qb. Qsnd may include granules, small pebbles, 

and organic material. Qsnd is gray in channel bottoms and 

brown in areas adjacent to cliffs, beaches, and active erosion. 

As mapped, this may include shoreline stabilizing riprap 

adjacent to water. 

Qsnd is mapped within Swanns Point and Jamestown Island

and along the length of the Colonial Parkway fronting the 

York River.

Fluvial Features and Processes—Qsnd is mapped 

submerged beneath the James River near Jamestown 

Island and may be a sand resource for shoreline 

nourishment. Shoreline Erosion, Sediment Transport, and Coastal 

Engineering Structures —these units are among the 

bottom-sediment units mapped in the James River. These 

sediments are constantly in flux in the channel and may be 

dredged periodically.

Sand and gravel

(Qsg)

Qsg is similar to Qbs, but with coarser grainsize. It consists of 

brown, coarse-grained sand, granules and pebbles. 

Qsg is mapped along the Back River near Jamestown.

Fluvial Features and Processes—Qsg is mapped 

submerged beneath the James River near Jamestown 

Island and may be a sand and/or gravel resource. 

Alluvium

(Qal)

Alluvium is deposited by rivers and streams in their channels. 

Qal consists of pebbly sand and sand with common silt layers 

and abundant organic material such as plant debris. 

Qal is mapped at Yorktown and along the Colonial Parkway.

Paleontological Resources—Qal contains organic 

material that may include plant debris and fossil pollen.

Hydrogeologic System at Yorktown Battlefield—Qal

may be part of the interlayered shallow system of aquifers 

and confining layers. Sandy sediments are part of the 

Columbia and Cornwallis Cave aquifers. Clay-rich layers 

are part of the Cornwallis Cave confining unit.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Groundwater Quantity and Quality —this unit is part 

of the regional shallow aquifer and confining layer system 

at Yorktown Battlefield.
Gray-shaded map units are not mapped within Colonial National Historical Park. Bold text refers to sections in report.

Colonial National Historical Park Map Unit Properties Table, Page 3 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY 

(late Pleistocene) 

Tabb Alloformation, 

undivided

(Qt)

Qt contains clay-rich, fine- to coarse-grained sand. 

Coastal Plain Sediments—Qt consists of fining-upward 

sequences.

Paleontological Resources—Qt may contain pollen and 

phytoliths (small mineral deposits within plants), as well as 

spores, and foraminifera that may yield a paleoecological 

reconstruction of the area for the past 37,000 years. These 

fossil remains may be part of Qm or Qom. None have 

been located within park boundaries to date.

Hydrogeologic System at Yorktown Battlefield—Qt is 

part of the interlayered shallow system of aquifers and 

confining layers. Sandy sediments of Qt are part of the 

Columbia aquifer. Clay-rich layers in Qt form part of the 

Cornwallis Cave confining unit. Qt is part of the 

Cornwallis Cave aquifer.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Groundwater Quantity and Quality—this unit is part of 

the regional shallow aquifer and confining layer system at 

Yorktown Battlefield. 

Building and Reshaping the Coastal Plain—Qt and 

overlying sediments (see Qm and Qom) may contain a 

record of paleoecological conditions for the past 37,000 

years. Northern boreal forests dominated the area until 

11,000 to 8,000 years before present when oak, hickory, 

and other temperate species thrived. Qt accumulated in 

fluvial, estuarine, and marginal and restricted marine 

environments. 

Tabb Alloformation, 

Poquoson member

(Qtp)

Qtp consists of layers of sand, silt, and clay. Qtp is up to 5 m 

(15 ft) thick. 

Qtp is mapped at Swanns Point and Jamestown Island. 

Fluvial Features and Processes—Qtp forms part of the 

low ridges south of Passmore Creek at Jamestown Island.

Coastal Plain Sediments—Qtp is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

None documented

Building and Reshaping the Coastal Plain—see 

description for Qt. Qtp and Qtl accumulated 

approximately 50,000 to 33,000 years ago. 

Tabb Alloformation, 

Lynnhaven and 

Poquoson members, 

undifferentiated 

(Qtlp)

Qtlp contains mixtures of fine- to coarse-grained sand and 

clay-rich sand. 

Coastal Plain Sediments—Qtlp is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

None documented Building and Reshaping the Coastal Plain—see 

description for Qt. 

Tabb Alloformation, 

Lynnhaven Member

(Qtl)

Qtl contains layers of silt, fine-grained sand, and clay. Qtl is 

up to 6 m (20 ft) thick. 

Qtl crops out at Jamestown Island and underlies the high 

ground first settled by the Europeans. It may have been a 

supply in early pottery and brick making.

Fluvial Features and Processes—Qtl underlies low, 

arcuate ridges on Jamestown Island.

Coastal Plain Sediments—Qtl is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

Paleontological Resources—Qtl includes paleochannel 

fill deposits that can include plant fragments or peat.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Building and Reshaping the Coastal Plain—see 

description for Qt. Qtp and Qtl accumulated 

approximately 50,000 to 33,000 years ago.

Tabb Alloformation, 

Sedgefield Member

(Qts)

Qts is coarser grained than Qt and contains pebbly sand, 

sand, and clay-rich silt layers. Qts is up to 15 m (50 ft) thick.

Qts is mapped at Yorktown. 

Coastal Plain Sediments—Qts is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

Paleontological Resources—Qts includes paleochannel 

fill deposits that can include plant fragments or peat. Qts

may contain marine fossils.

Building and Reshaping the Coastal Plain—see 

description for Qt. Qts dates at least in part to 

approximately 130,000 to 80,000 years ago.

QUATERNARY

Elsing Green 

Alloformation 

(Qeg)

Qeg consists of muddy, fine- to medium-grained sand grading 

downward to coarse-grained sand, granules, and pebbles. 

Phosphate mineral occur locally. Qeg is up to 4 m (15 ft) thick, 

with thicker areas in paleochannels in the York and James 

rivers. 

Qeg is mapped at College Creek and along the Colonial 

Parkway fronting the York River. 

Coastal Plain Sediments—Qeg is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

None documented

Building and Reshaping the Coastal Plain—Qeg dates 

at least in part to approximately 125,000 to 130,000 years 

ago.
Gray-shaded map units are not mapped within Colonial National Historical Park. Bold text refers to sections in report.

Colonial National Historical Park Map Unit Properties Table, Page 4 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY 

(middle Pleistocene) 

Shirley

Alloformation

(Qsh)

Qsh contains pebble to boulder sand layers, silt and clay 

layers, with scattered organic-rich beds of silt and peat. Qsh is 

up to 24 m (80 ft) thick in paleochannels. The contact with the 

overlying Qt is disconformable. 

Qsh is mapped at Jamestown Island, Yorktown, and along the 

Colonial Parkway. 

Coastal Plain Sediments—Qsh is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

Paleontological Resources—Qsh contains organic 

material that may include plant debris and fossil pollen. In 

situ tree stumps, leaves, and seeds of cyprus, oak, and 

hickory trees are common in Qsh. Crassostrea virginica, 

Mulinia, Noetia, and Mercenaria, among other mollusks 

also occur in Qsh. An Astrangia (coral) fossil was dated for 

an approximate age of 184,000 years before present in 

Qsh. None have been located within park boundaries to 

date.

Hydrogeologic System at Yorktown Battlefield—Qsh

is part of the interlayered shallow system of aquifers and 

confining layers. Sandy sediments of Qsh are part of the 

Columbia aquifer. Clay-rich layers in Qsh form part of the 

Cornwallis Cave confining unit. Qsh is the part of the 

Cornwallis Cave aquifer.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Geologic Hazards and Risks—Qsh underlies local 

buildings with relatively elevated radon levels.

Groundwater Quantity and Quality—this unit is part of

the regional shallow aquifer and confining layer system at 

Yorktown Battlefield.

Building and Reshaping the Coastal Plain—Qsh was 

part of a series of complex erosional surfaces, channel 

incisions, and sedimentary fill events during local sea level 

changes. Qsh accumulated in spatially complex fluvial, 

estuarine, and nearshore marine settings. Qsh

accumulated on the York-James Peninsula approximately 

400,000 to 250,000 years ago. 

QUATERNARY 

(middle(?) Pleistocene) 

Chuckatuck 

Alloformation

(Qc)

Qc consists of pebbly sand, sand, silt, and clay layers. Qc is 

locally up to 8 m (26 ft) thick. Upper and lower contacts of Qc

are unconformable. 

Qc is mapped at Yorktown Battlefield. 

Coastal Plain Sediments—Qc is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

Paleontological Resources—Qc contains Ophiomorpha

burrows as trace fossils. None have been located within 

park boundaries to date.

Hydrogeologic System at Yorktown Battlefield—Qc is 

part of the interlayered shallow system of aquifers and 

confining layers. Sandy sediments of Qc are part of the 

Columbia aquifer. Clay-rich layers in Qc form part of the 

Cornwallis Cave confining unit. Qc is the part of the 

Cornwallis Cave aquifer.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Groundwater Quantity and Quality—this unit is part of 

the regional shallow aquifer and confining layer system at 

Yorktown Battlefield. 

Building and Reshaping the Coastal Plain—Qc formed 

in fluvial, estuarine, and restricted marine environments 

associated with sea level changes during the Pleistocene. 

QUATERNARY

(early Pleistocene) 

Charles City 

Alloformation

(Qcc)

Qcc is similar in composition to Qsh with pebble to boulder 

sand, interlayered with cross-bedded sand, and silt and clay.

Qcc is mapped at Yorktown Battlefield and near College 

Creek at the Colonial Parkway. 

Coastal Plain Sediments—Qcc is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

None documented

Building and Reshaping the Coastal Plain—Qcc was 

part of a series of complex erosional surfaces, channel 

incisions, and sedimentary fill events during local sea level 

changes.
Gray-shaded map units are not mapped within Colonial National Historical Park. Bold text refers to sections in report.

Colonial National Historical Park Map Unit Properties Table, Page 5 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

QUATERNARY 

(early Pleistocene) 

Windsor Formation

(Qw)

Qw contains clay-rich, fine- to coarse-grained sand that 

overlies fine- to coarse-grained, pebble-rich sand layers. Qw

has a local maximum thickness of about 12 m (40 ft). The 

contact between Qw and overlying Qsh is disconformable.

Qw is mapped along the Colonial Parkway and at Yorktown.

Coastal Plain Sediments—Qw is among the younger, 

fluvial-estuarine deposits with highly variable 

compositions.

Paleontological Resources—Fossils are not common for 

this unit and none have been located within park 

boundaries to date. Elsewhere, Qw contains in situ vertical 

knobby burrows similar to those formed by Calianassa 

major (modern ghost shrimp). Qw also displays mollusk 

molds formed in goethite, hematite, and limonite minerals 

from reworked Ty mollusks. 

Hydrogeologic System at Yorktown Battlefield—Qw

is part of the interlayered shallow system of aquifers and 

confining layers. Sandy sediments of Qw are part of the 

Columbia aquifer. Qw is also part of the Cornwallis Cave 

aquifer.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Groundwater Quantity and Quality—this unit is part of 

the regional shallow aquifer and confining layer system at 

Yorktown Battlefield. 

Building and Reshaping the Coastal Plain—Qw was 

part of a series of complex erosional surfaces, channel 

incisions, and sedimentary fill events during local sea level 

changes. Qw accumulated in fluvial, estuarine, tidal flat, 

and restricted marine settings. Qw was deposited 

approximately 1.5 million years ago.

Moorings unit of 

Oaks and Coch 

(1973)

(Qm)

Qm consists of massively bedded sand or clay. None documented None documented

Building and Reshaping the Coastal Plain—Qm was 

part of a series of complex erosional surfaces, channel 

incisions, and sedimentary fill events during local sea level 

changes.

Bacons Castle 

Formation 

(Qbc)

Qbc is composed of massively bedded and lenticular to flaserbedded layers of sand, silt, and clay. Basal layers commonly 

contain pebbles and coarser sand grains. Qbc ranges in 

thickness from 14 to 21 m (45 to 70 ft). 

Qbc crops out in Swanns Point and along the Colonial 

Parkway.

Coastal Plain Sediments—Qbc has flaser bedding in 

which mud streaks or lenses occur in ripple troughs, but 

not on the crests.

Paleontological Resources—Fossils are not common for 

this unit and none have been located within park 

boundaries to date. Qbc may contain invertebrate 

burrows.

Subsurface Geologic Features and the Chesapeake 

Bay Impact Crater—Qbc overlies regional faults that may 

affect shallow-aquifer dynamics. 

Hydrogeologic System at Yorktown Battlefield—Qbc

is part of the interlayered shallow system of aquifers and 

confining layers. Clay-rich layers in Qbc form part of the 

Cornwallis Cave confining unit. Qbc is part of the 

Cornwallis Cave aquifer.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Geologic Hazards and Risks—Qbc underlies local 

buildings with relatively elevated radon levels.

Groundwater Quantity and Quality—this unit is part of 

the regional shallow aquifer and confining layer system at 

Yorktown Battlefield. 

Building and Reshaping the Coastal Plain—Qbc was 

part of a series of complex, shifting depositional 

environments resulting from climatic and sea level 

changes. Qbc accumulated in fluvial, estuarine, tidal flat, 

and possibly marine settings approximately 2.3 to 2.0 

million years ago.

NEOGENE

(late Pliocene) 

Cold Harbor 

Formation 

(Tch)

Tch contains yellow to red, muddy, fine- to coarse-grained 

sand with rare granules. Some lenticular clay layers may reach 

9.1 m (30 ft) in thickness. Tch also commonly includes a basal 

gravel layer with large pebbles. Total thickness of Tch ranges 

up to 24.2 m (80 ft). Tch unconformably overlies Tymh and 

Tc. 

Tch is mapped in creek drainages crossed by the Colonial 

Parkway.

Paleontological Resources—burrows such as 

Ophiomorpha nodosa are common for Tch. 

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Building and Reshaping the Coastal Plain—Tch

accumulated in marginal-marine, wave-dominated deltaic, 

shallow marine, and tidal flat/channel settings. Tch was 

deposited during a period of sea-level rise. 
Gray-shaded map units are not mapped within Colonial National Historical Park. Bold text refers to sections in report.

Colonial National Historical Park Map Unit Properties Table, Page 6 of 6 

Age Map Unit

(Symbol) Geologic Description Geologic Features and Processes Geologic Resource Management Issues Geologic History

NEOGENE

(late Pliocene) 

Yorktown 

Formation, Moore 

House Member

(Tymh)

Tymh is one of four members of the Yorktown Formation (Tc) 

and consists of a shell hash of coquina layer and sandy, clayey

silt that is yellowish to brown in color. The sand layers coarsen 

downward from very-fine sand to granules. Tymh is typically 2 

to 3 m (7 to 10 ft) thick. 

See descriptions for Tc See descriptions for Tc

Building and Reshaping the Coastal Plain—Tymh

accumulated in a fluvial-estuarine, and tidal channel

settings.

NEOGENE

(Pliocene and early Pliocene)

Chesapeake Group, 

Yorktown and 

Eastover formations, 

undivided

(Tc)

Tc includes interlayered shell-rich, fine-grained sand, clay-rich 

fine-grained sand, and silty fine- to very fine-grained sand. 

The Yorktown Formation contains interlayered shell-rich sand 

and fine-grained sand with dark brown clay-rich sand and clay 

at the top of the unit. Locally, the Yorktown Formation ranges 

in thickness between 12 and 14 m (39 and 45 ft). Its 

maximum thickness at Yorktown is 16.8 m (55 ft). The 

contacts between the Yorktown and overlying and underlying 

units are disconformable. Recent mapping and drilling on the 

James-York Peninsula have revealed the previously used 

“Sedley Formation” to be a weathering layer within the 

Yorktown Formation.

The Eastover Formation consists of sand with interlayers of 

fossiliferous sand. The Eastover Formation varies in thickness 

from 5 to 28 m (16 to 92 ft). The contacts between The 

Eastover Formation and underlying older units, as well as 

overlying units are disconformable.

Tc is mapped at Swanns Point, Yorktown, and along the 

Colonial Parkway.

Coastal Plain Sediments—Tc is among the older, thin, 

tabular, fossiliferous marine deposits.

Paleontological Resources—The Yorktown Formation

contains shells and shell debris (coquina). The first figured 

and described fossil from North America (ca. 1687) may 

have come from this unit—Chesapecten jeffersonius, 

named the state fossil of Virginia in 1993. The Yorktown 

Formation is rich in mollusks (at least 600 molluscan 

species) and other species such as Turritella (gastropod), 

Crepidula (gastropod), Striarca centenaria (bivalve), Tellina

(bivalve), Balanus (barnacles), Scaphopoda (tusk-shelled 

mollusks), Yoldia limatula (bivalve), bryozoans, 

brachiopods, sponges, corals, annelid worms, decapod 

burrows, foraminifera, ostracodes, and echinoids. 

Vertebrate fossils discovered in the Yorktown Formation

include fish bones, shark teeth, walrus jaw (Prorosmarus 

alleni), whale (Balaena) vertebrae, and a whale tooth.

The Eastover Formation contains fossil-bearing layers that 

may include foraminifera, diatoms, palynomorphs (pollen 

and spores), dinoflagellates, brachiopods, gastropods, 

bivalves, ostracodes barnacles, crabs, echinoids, sharks, 

bony fish, auks, whales, and burrows; mollusks from the 

Eastover Formation may also be reworked into the 

Yorktown Formation.

Subsurface Geologic Features and the Chesapeake 

Bay Impact Crater —the deposition of Tc coincides with 

active Cenozoic faulting that may affect shallow-aquifer 

dynamics.

Hydrogeologic System at Yorktown Battlefield—Tc is 

part of the interlayered shallow system of aquifers and 

confining layers. Clay-rich layers in Tc form part of the 

Cornwallis Cave confining unit. Tc is the part of the 

Cornwallis Cave aquifer. Tc is part of the Yorktown 

confining unit. The Yorktown Formation is the lowermost 

part of the interlayered shallow system of aquifers and 

confining layers. The Yorktown Formation is the primary 

portion of the Cornwallis Cave aquifer and part of the 

Yorktown-Eastover aquifer, both of which underlie nearly 

the entire battlefield.

Paleontological Resource Inventory, Monitoring, and 

Protection—the park does not yet have a site-specific 

paleontological resource management plan.

Geologic Hazards and Risks—Lateral heave within layers 

of the Yorktown Formation lead to local slope instability. 

Tc underlies local buildings with relatively elevated radon 

levels.

Groundwater Quantity and Quality—this unit is part of 

the regional shallow aquifer and confining layer system at 

Yorktown Battlefield. the Eastover Formation portion of 

this unit is part of the regional shallow aquifer and 

confining layer system at Yorktown Battlefield, but is 

located at depths that are not reached by local stream 

incision.

Karst Landscape Management—dissolution of 

carbonate-rich layers within Tc causes sinkhole formation 

at Yorktown Battlefield. 

Yorktown Formation Shrink-and-Swell Clays—clays 

within the Yorktown Formation swell when water 

saturated and shrink upon drying. The resulting volume 

changes can cause damage to roads and overlying 

structures. 

Abandoned Mineral and Disturbed Lands—Cornwallis 

Cave was excavated into coquina layers of the Yorktown 

Formation. The roof of the cave is failing. 

Building and Reshaping the Coastal Plain—the 

Yorktown Formation accumulated in a variety of shallow 

marine settings including open marine, lagoon or other 

restricted marine, and barrier environments. Climate was 

relatively warmer during the deposition of the Yorktown 

Formation resulting in subtropical species flourishing. Age 

dates for the Yorktown Formation range from 4.5 to 2.5 

million years ago. 

The Eastover Formation accumulated in shallow marine 

depositional environments during the Late Miocene. The 

Eastover Formation contains a record of a climate shift 

from older, cooler, open marine phase, to a younger, 

subtropical, shallow marine phase. The Eastover Formation

may be as old as 11 million years.