America's Volcanic Past -
Washington D.C.

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Volcanic Highlights and Features:
[This list is just a sample of various Washington D.C. volcanic features or events and is by no means inclusive.]

• Washington D.C.
• Washington D.C.'s Volcanic Rocks
• Washington D.C.'s Volcanic Building Stones
• Washington D.C.'s Buildings
• Great Falls of the Potomac

Volcanic Rocks of the Piedmont Plateau:¹
The Piedmont Plateau province lies west of the Coastal Plain. The Piedmont rocks in and near Washington D. C., are crystalline metamorphic rocks that are quite hard and resist weathering; they contain veins of quartz and pegmatite and in many places have been intruded by igneous rock (formed from molten rock from inside the Earth). Most of the crystalline rocks on the uplands were deposited about 550-600 million years ago.

Volcanic Rocks of the Triassic Lowland Province:¹
The rocks of the Triassic Lowland province, deposited about 200 million years ago, are red shales and red and gray sandstones and conglomerates, which weather to a reddish soil. Near Washington these sedimentary rocks are as much as 5,000 feet thick. In some places, they have been intruded by trap rock (resistant fine-grained igneous rock).

Volcanic Rocks of the Blue Ridge Province:¹
The Blue Ridge province, lying west of the Triassic Lowland, is a region of north- and northeast-trending valleys and ridges underlain by folded metamorphic and igneous rocks that were formed more than 500 million years ago. Near Washington, the rocks consist predominantly of granite, greenstone (metamorphosed by great heat and pressure from basaltic lava flows), and quartzite.

First Building Stones - Piedmont Metamorphic Rocks:¹
The building stones used by the earliest European settlers were the crystalline rocks of the Piedmont, which were quarried from outcrops along the Potomac River and Rock Creek. One type, known to geologists as Sykesville Formation, is still quarried west of the city and used for flagstone. (See Piedmont above)

Granites:¹
Starting in the 1850's, granite quarried at Dix Island, Maine, was shipped by sea to Washington and was used for facings and columns in the Treasury Building. Granites from New England, Georgia, and North Carolina and marbles from Vermont, Tennessee, and Georgia were used for almost all government buildings after the Civil War until the First World War.

Arlington Memorial Bridge:¹
Piers, Georgia granite; facing of spans, granite from Georgia, Vermont, North Carolina, New Hampshire, and Maine. The granite from North Carolina (Mount Airy, Surry County): very light gray, medium textured, biotite granite, biotite is unequally distributed; some rock contains almost no biotite. Probably Paleozoic age.

Capitol Building Steps to the West Front:¹
Granite from Vermont - Barre, Washington County. Gray to white. Medium to fine grained. Contains about 65 percent feldspar, 27 percent quartz, and 8 percent biotite mica. Ordovician age.

Capitol Building:¹
Building Stones: Center building, Virginia Aquia Creek sandstone; Senate and House wings, Lee, Mass., dolomitic marble; Rotunda floor, Seneca, Md., sandstone; columns of wings, Cockeysville, Md., white marble; center steps, Renville, Minn., granite; west elevation steps, Mount Airy, N.C., granite; west elevation balustrade, Vermont marble; interior balustrades and columns of stairs leading to House and Senate galleries and wall of Marble Room, Tennessee marble; east front exterior, Georgia White Cherokee marble (covering original Aquia Creek sandstone); 24 exterior columns, Georgia marble; interior columns, Statuary Hall, Old Senate Chamber and foyer, Maryland Potomac marble; columns in Crypt and those with corn and tobacco leaves, Virginia Aquia Creek sandstone; columns, ground floor east front addition, Colorado brecciated marble.

Commerce Department:¹
Exterior, first and second floors, Stony Creek granite, Connecticut Coarse-grained, with large pink feldspar crystals in a gray mass of smaller crystals. Precambrian age; interior, Georgia and Missouri marble.

Department of Agriculture, North Building:¹
Central part, Georgia white Cherokee marble; wings, Vermont marble; foundation, Massachusetts granite; interior, Tennessee marble.

Department of the Interior Building:¹
Building Stones: Foundation and steps, Milford, Mass., granite; exterior, Indiana limestone; interior, Tennessee marble.

Executive Office Building (Old State-War-Navy Building):¹
Building Stones: Exterior, granite from Virginia, Maine, and Massachusetts; subbasement, Maryland sandstone.

FDR Memorial:¹
Carnellan granite, quarried in South Dakota, with a small amount of "Academy Black" granite, quarried in California and fabricated in Cold Spring, Minnesota.

Federal Reserve Building:¹
Exterior, Georgia marble; foundation, Massachusetts granite; fountains, Pennsylvania black diabase.

Fountains on the Ellipse at Constitution Ave:¹
Granite from Minnesota - Redwood and Renville Counties. Greenish-gray medium-grained biotite gneiss; pale-pink biotite granite or quartz diorite; and a granite gneiss with distinct banding, black knots of biotite, and large isolated feldspar crystals. Precambrian age.

Freedom Plaza:¹
Border, red-pink granite from Llano, Texas; interior, L'Enfant's original plan for Washington portrayed with streets of Georgia marble, waterways of New York sandstone, and city blocks of California granite.

Jefferson Memorial:¹
Exterior columns and walls, Vermont white marble; foundation and circular terraces, Georgia granite; floors, Tennessee pink and gray marble; interior dome, Indiana limestone.

Korean War Veterans Memorial:¹
Wall was made of "Academy Black" granite from California, sand blasted in Cold Spring, Minnesota, with more than 2,500 photographic, archival images from the war; on the base of the pool highly reflective black granite from Canada.

Library of Congress:¹
Building Stones: Concord, New Hampshire, granite.

Lincoln Memorial:¹
Reflecting pool, North Carolina granite; foundation steps, Massachusetts granite; memorial building, Colorado marble; statue, Georgia marble; base of statue and floors, Tennessee marble; columns and lintels, Indiana limestone.

Museum of American History of the Smithsonian Institution:¹
Minnesota granite, rarely seen in Washington's government buildings before World War II, is now being used more frequently. This material serves as steps and trim around the Museum of American History of the Smithsonian Institution and is used in fountains in the Ellipse on Constitution Avenue. Some of these granites have been dated by the U. S. Geological Survey as 3.5 billion years old, the oldest rocks in North America.

Museum of American History, Smithsonian Institution:¹
Exterior, mainly Tennessee light-pink marble; curbs and fountain steps, Minnesota pearl pink granite. Note light-red irregularly shaped feldspar crystals.

Museum of Natural History, Smithsonian Institution:¹
Exterior, ground floor, Massachusetts pink granite; two main floors, Vermont white granite; top floor, Mount Airy, N. C., white granite; doorway on Mall side, greenish-pink granite.

National Archives Building:¹
Exterior, Milford, Massachusetts granite and Indiana limestone; interior, Missouri golden vein marble; foyer, Tennessee marble.

Post Office Pavilion and Nancy Hanks Center Tower:¹
Exterior, Maine granites; interior mezzanine floor, white and orange marble with green serpentine.

Rayburn Building:¹
Building Stones: Exterior walls, Georgia White Cherokee marble and Vermont marble; perimeter base, New Hampshire pink granite; east and west courts and paving borders, pink granite (note large, regularly shaped pink feldspar crystals); inner court, base of Salisbury, North Carolina, pink granite with Indiana limestone above.

Treasury Building:¹
Starting in the 1850's, granite quarried at Dix Island, Maine, was shipped by sea to Washington and was used for facings and columns in the Treasury Building. Exterior, the original part along 15th Street was originally built of Virginia Aquia Creek sandstone, replaced in large part by Dix Island, Maine, granite; remainder, Dix Island and Milford, Mass., granite; foundation, Maryland crystalline rocks. Patio, Seneca, Md., red sandstone; Catskill, N.Y., green sandstone; and concrete.

Union Station:¹
Building Stones: Vermont granite.

U.S. Navy Memorial:¹
Quebec, Canada, black granite, Rhode Island light-gray granite; patio, Catskills, N.Y., green sandstone; border, Deer Isle, Maine, lavender granite.

Vietnam Veterans Memorial:¹
Building Stone: Black granite quarried near Bangalore, India; cut and fabricated in Barre, Vermont; and sandblasted in Memphis, Tennessee.

Zero Milestone:¹
Granite from Massachusetts - Milford, Worcester County. Light pinkish to greenish gray, with spots of black biotite mica that may form bands. Medium to coarse textured. Precambrian age.

Great Falls of the Potomac

Great Falls of the Potomac, McLean, Virginia:²
Located just 15 miles from the Nation's capital, the Great Falls of the Potomac (a name given the area by the first European colonists) is considered the most spectacular natural landmark in the D.C. metropolitan area. Here, the Potomac River builds up speed and force as it falls over a series of steep, jagged rocks and flows through a narrow gorge. This dramatic scene makes Mather Gorge, named after the first director of the National Park Service, a popular site with local residents and tourists from around the world who are visiting the Washington area. The falls consist of cascading rapids and several 20 foot waterfalls with a total 76 foot drop in elevation over a distance of 3500 feet. Arising from a calmer and much broader flow upstream, the Potomac constricts at Great Falls from 2500 feet just above the falls to between 60 and 100 feet along the gorge for over a mile. The Great Falls of the Potomac display the steepest and most spectacular fall line rapids of any eastern river. The geologic history of the falls is an interesting one. After the last ice age, the ocean levels dropped forcing the Potomac river to carve deeper in its path to the sea. The overlying rock was eroded away exposing a much harder, resistant rock formation called the Piedmont. This hard layer is principally made up of highly metamorphic and igneous rock, and may be seen throughout the park. For thousands of years the Potomac river has eroded the bedrock, causing the falls to recede upstream from a point 9 miles downstream near Chain Bridge to its current position at Great Falls. Joint fault plains, natural fissures in the rock substrata where shifting has occurred, exist in many places in the Piedmont Formation between Chain Bridge and the Great Falls. These areas of faulting have loosened the rock, forming areas of weakness. The force of the river has eroded along these areas changing the river's course to its current position. As one walks along the cliff tops, evidence of the ancient river beds can be seen in well-rounded boulders, smoothed surfaces and grooves, and beautifully formed potholes which were once formed on the ancient riverbed. The metamorphic rocks provide jagged rocky surfaces and high-walled cliffs, stark and pristine against the crashing waters of the Potomac at the falls and along Mather Gorge.

Excerpts from:
1) Building Stones of Our National's Capital: USGS General Interest Publication, OnLine Version 1.0, 1999
2) U. S. National Park Service Website, Great Fall Park Website, 2002

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