<P> After the assassination of civil rights leader Dr. Martin Luther King, Jr., on April 4, 1968, riots broke out in the District, primarily in the U Street, 14th Street, 7th Street, and H Street corridors, centers of black residential and commercial areas . The riots raged for three days until more than 13,600 federal troops stopped the violence . Many stores and other buildings were burned; rebuilding was not completed until the late 1990s . </P> <P> In 1973, Congress enacted the District of Columbia Home Rule Act, providing for an elected mayor and 13 - member council for the District . In 1975, Walter Washington became the first elected and first black mayor of the District . </P> <P> Washington, D.C., is located in the mid-Atlantic region of the U.S. East Coast . Due to the District of Columbia retrocession, the city has a total area of 68.34 square miles (177.0 km), of which 61.05 square miles (158.1 km) is land and 7.29 square miles (18.9 km) (10.67%) is water . The District is bordered by Montgomery County, Maryland, to the northwest; Prince George's County, Maryland, to the east; and Arlington and Alexandria, Virginia, to the south and west . </P> <P> The south bank of the Potomac River forms the District's border with Virginia and has two major tributaries: the Anacostia River and Rock Creek . Tiber Creek, a natural watercourse that once passed through the National Mall, was fully enclosed underground during the 1870s . The creek also formed a portion of the now - filled Washington City Canal, which allowed passage through the city to the Anacostia River from 1815 until the 1850s . The Chesapeake and Ohio Canal starts in Georgetown and was used during the 19th century to bypass the Little Falls of the Potomac River, located at the northwest edge of Washington at the Atlantic Seaboard fall line . </P>

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