the district three votes in the Electoral College for the election of president and vice president, but still not affording the city's residents representation in Congress. After the assassination of civil rights leader 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, which were predominantly black residential and commercial areas. The riots raged for three days until more than 13,600 federal troops and Washington, D.C. Army National Guardsmen stopped the violence. Many stores and other buildings were burned, and rebuilding from the riots was not completed until the late 1990s. 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 district's first elected and first black mayor. Geography Washington, D.C. is located in the mid-Atlantic region of the U.S. East Coast. The city has a total area of , of which is land and (10.67%) is water. The district is bordered by Montgomery County, Maryland to the northwest; Prince George's County, Maryland to the east; Arlington County, Virginia to the west; and Alexandria, Virginia to the south. Washington, D.C. is from Baltimore, from Philadelphia, from New York City, from Pittsburgh, from Charlotte, and from Boston. 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 the city at the Atlantic Seaboard fall line. The highest natural elevation in the district is above sea level at Fort Reno Park in upper northwest Washington, D.C.. The lowest point is sea level at the Potomac River. The geographic center of Washington is near the intersection of 4th and L Streets NW. The district has of parkland, about 19% of the city's total area and the second-highest percentage among high-density U.S. cities after Philadelphia. The city's sizable parkland