Wednesday, September 10, 2014

Topography of the Washington, D.C., area, overlaid with city streets and boundaries of the area.

Look closely: You'll see that much of downtown Washington is basically on a flat plain, with a curving natural escarpment to the northeast, north, and northwest.

On July 9, 1790, Congress passed the Residence Act, which approved the creation of a national capital on the Potomac River. The exact location was to be selected by President George Washington, who chose a portion of the states of Maryland and Virginia on January 24, 1791. Originally, government officials did not foresee that the city of Washington would expand to fill the boundaries of the entire District of Columbia. The "Federal City", or City of Washington, originally lay within an area bounded by Boundary Street (northwest and northeast), 15th Street Northeast, East Capitol Street, the Anacostia River, the Potomac River, and Rock Creek. Boundary Street was renamed Florida Avenue in 1890.

Florida Avenue passes along the foot of the hilly terrain which basically marks the Federal City. These hills are the Wicomico-Sunderland Escarpment, which is part of the Atlantic Seaboard fall line. The escarpment help marks the transition between the Appalachian Piedmont region north of the avenue and the flat Atlantic Coastal Plain terrain of the city's downtown area to the south.

You will also notice the natural valley in the escarpment to the north of downtown, which is where most of the city expanded in the late 1800s. Note, too, the flat land along the Potomac River next to Georgetown, which is on the Georgetown Heights. Beyond that, you can see how a natural northeast-southwest running ridge forms Nebraska Avenue NW, and beyond that is the gentle slope of AU Park and Spring Valley.

In the lower central image, on the left bank of the Potomac is Alexandria on the flat land there. On the right bank are the flat farmland that is now Joint Base Anacostia-Bolling, and the high escarpment behind it that used to hold Civil War forts. (That's South Capitol Street hugging the base of the escarpment.) Slicing southwest through Anacostia is Oxon Run, and through Maryland is Broad Creek. South of Alexandria, that's Cameron Run. These creeks have carved deeply into landscape.

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