National Park Service U.S. Department of the Interior Natural Resource Program Center Rock Creek Park Geologic Resources Inventory Report Natural Resource Report NPS/NRPC/GRD/NRR—2009/146 THTHISIS PAPAGE:GE: Rapids Bridge (built in 1934) over Rock Creek. Rocky streamstreamss aarre a hahalllmarklmark of tthehe PiPiedmontedmont Province, part of the metamorphosed core of the Appalachian Mountains. Library of Congress, Prints and Photographs Divivisision,on, HiHiststorioricc AmeriAmeri-- can Engineering Record, HAER DC,WASH,569-1. ON THE COVER: Boulder Bridge also spans Rock Creek. Built in 1902, it is an early examplele of rustic architecture in NPS infrastructure. Although the stones were collected outside of the park, they are typical of the weathered cobbles found within Rock Creek Park—eroded remanants of the core of the Appa- lachian Mountains. NPS Photo. Rock Creek Park Geologic Resources Inventory Report Natural Resource Report NPS/NRPC/GRD/NRR—2009/146 Geologic Resources Division Natural Resource Program Center P.O. Box 25287 Denver, Colorado 80225 December 2009 U.S. Department of the Interior National Park Service Natural Resource Program Center Denver, Colorado The Natural Resource Publication series addresses natural resource topics that are of interest and applicability to a broad readership in the National Park Service and to others in the management of natural resources, including the scientific community, the public, and the NPS conservation and environmental constituencies. Manuscripts are peer-reviewed to ensure that the information is scientifically credible, technically accurate, appropriately written for the intended audience, and is designed and published in a professional manner. Natural Resource Reports are the designated medium for disseminating high priority, current natural resource management information with managerial application. The series targets a general, diverse audience, and may contain NPS policy considerations or address sensitive issues of management applicability. Examples of the diverse array of reports published in this series include vital signs monitoring plans; "how to" resource management papers; proceedings of resource management workshops or conferences; annual reports of resource programs or divisions of the Natural Resource Program Center; resource action plans; fact sheets; and regularly-published newsletters. Views, statements, findings, conclusions, recommendations and data in this report are solely those of the author(s) and do not necessarily reflect views and policies of the U.S. Department of the Interior, National Park Service. 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NPS 821/100278, December 2009 ii Contents Figures .......................................................................................................................... iv Executive Summary ...................................................................................................... v Introduction ................................................................................................................... 1 Purpose of the Geologic Resources Inventory ........................................................................................................... 1 Park History and Setting ............................................................................................................................................. 1 Geologic Setting ......................................................................................................................................................... 2 Geologic Issues ............................................................................................................. 5 Erosion, Slope Processes, and Stability ..................................................................................................................... 5 Sediment Load and Channel Storage ......................................................................................................................... 5 Water Issues............................................................................................................................................................... 6 Recreational Demands ............................................................................................................................................... 7 General Geology and Miscellaneous Action Items ..................................................................................................... 7 Geologic Features and Processes ............................................................................... 9 The Rock Creek Shear Zone and Other Structures .................................................................................................... 9 Terraces of the Potomac River ................................................................................................................................. 10 Potential Paleontological Resources ........................................................................................................................ 10 Geologic Influences on the History of Rock Creek Park ........................................................................................... 10 Map Unit Properties .................................................................................................... 16 Geologic History.......................................................................................................... 23 Taconic Orogeny ...................................................................................................................................................... 23 Acadian Orogeny ...................................................................................................................................................... 23 Alleghanian Orogeny ................................................................................................................................................ 24 Triassic Extension to the Present ............................................................................................................................. 24 Glossary ....................................................................................................................... 28 References ................................................................................................................... 31 Appendix A: Geologic Map Graphic .......................................................................... 35 Appendix B: Scoping Summary ................................................................................. 37 Appendix C: Report of the National Park Service Monitoring Workshop: Planning for the Future in the National Capital Network p. 29-43 ........................................... 40 Appendix D: Geoindicators Notes ............................................................................. 49 Attachment 1: Geologic Resources Inventory Products CD ROCR Geologic Resources Inventory Report iii Figures Figure 1. Map showing the physiographic provinces and selected NPS areas of the National Capital Region .............. 3 Figure 2. Map of Rock Creek Park ................................................................................................................................. 4 Figure 3. Aerial view of Rock Creek Park ....................................................................................................................... 8 Figure 4. Generalized geologic map of Rock Creek Valley .......................................................................................... 12 Figure 5. Flattened and sheared metamorphosed conglomerate of the Cambrian Laurel Formation .......................... 13 Figure 6. Historic (1925) image of reverse fault near the intersection of Adams Mill Road and Clydesdale Place ...... 13 Figure 7. Petrified cypress trunk on display at the Rock Creek Park nature center...................................................... 14 Figure 8. Old Stone House in Georgetown .................................................................................................................. 14 Figure 9. Pierce Mill in 1940s ....................................................................................................................................... 15 Figure 10. Pierce Mill dam and waterfall ...................................................................................................................... 15 Figure 11. Geologic timescale ...................................................................................................................................... 26 Figure 12. Evolution of the landscape in the National Capital Region .......................................................................... 27 iv NPS Geologic Resources Division