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Washington Co., Maryland, USA

This county in western Maryland is underlain by sedimentary rocks that have been spectacularly folded and faulted by the late Paleozoic Allegheny orogeny (mountain building period). These folded rocks are beautifully displayed at the I-70 road cut at Sideling Hill. Differential erosion has sculpted these rocks into alternating high and low lands known as the scenic "Valley and Ridge Province" of the Appalachians. The rocks are generally unmineralized, little metamorphosed sandstone, shales, limestones and coal beds ranging in age from Ordovician to Pennsylvanian. They are at times profusely fossiliferous. Many of these lithologies are well exposed in road cuts, most notably the magnificent syncline exposed in the Sideling Hill road cut on I-68. Cambrian limestone abounds in the Hagerstown Valley, an extension of the Great Valley. On the eastern side of this valley, forming the eastern edge of the County, is the Blue Ridge Province, where older, more metamorphosed sedimentary rocks and volcanic rocks of Proterozoic to Cambrian age occur. These are well exposed in Greenbrier and Washington Monument State Parks on South Mountain, which is held up by the very resistant Cambrian Wevertown Quartzite. Some of the volcanic rocks host small native copper deposits.

Mineral List

Mineral list contains entries from the region specified including sub-localities
var: Blue Quartz
var: Smoky Quartz


11 entries listed. 7 valid minerals.

Localities in this Region


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Cloos, E. et. al. (1951) Washington County: Maryland Geological Survey: County Report, 333 p.

Brezinski, D. K. (1997) Lithostratigraphy of the western Blue Ridge cover rocks in Maryland: Maryland Geological Survey: Report of Investigations 55, 55 pages plus map.

Schmidt, M.F. & M. F. Schmidt Jr. (2010) Maryland's Geology: Schiffer Publications, 164 p.

Means, J. (2010) Roadside geology of Maryland, Delaware and Washington, D.C.: Wild Horizons Publishers, 346 p.

External Links

Geological Map of Garrett, Alleghany and Western Washington Counties, Maryland http://www.mgs.md.gov/geo/wmdgeomap.html

Geology of the Sideling Hill road cut: http://www.mgs.md.gov/esic/brochures/sideling.html

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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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