aboard a British ship, wrote "The Star-Spangled Banner," a poem later set to music as the national anthem of the United States. Today, a red, white, and blue buoy marks the spot where was anchored. Geography Watershed The Patapsco has a watershed area (including the water surface) of . Through most of its length, the Patapsco is a minor river, flowing for the most part through a narrow valley. The last , however, form a large tidal estuary inlet of Chesapeake Bay. The inner part of this estuary provides the harbor of Baltimore, composed of the Northwest Harbor and the Middle Branch including Thoms Cove. (See Baltimore Inner Harbor.) The Patapsco estuary is south of the Back River and north of the Magothy River. The Patapsco River forms the harbor as it empties into the Chesapeake Bay. Besides Baltimore, the river also flows through Ellicott City (the county seat of Howard County) and Elkridge. The Patapsco River mainstem begins at the confluence of the North and South Branches, near Marriottsville, approximately west of downtown Baltimore. The South Branch rises further west at Parr's Spring, where Howard County, Carroll, Frederick, and Montgomery counties meet. The latter begins at elevation on Parr's Ridge, just south of Interstate 70 and east of Ridge Road (Highway 27), south of Mount Airy, Maryland. The South Branch Patapsco River traces the southern boundary of Carroll County and the northern boundary of Howard County. The first land record regarding Parr's Springs dates from 1744, when John Parr laid out a tract he called Parr's Range. During the Civil War, Parr's Spring was a stop for the Army of the Potomac's Brig. Gen. David M. Gregg's cavalry, on June 29, 1863, while en route to Gettysburg, Pennsylvania. Parr's Spring was dug to form a pond in the 1950s, filled by seven spring heads that form the headwaters of the South Branch of the Patapsco River. The North Branch flows southward from its origins in Carroll County. Liberty Dam and its reservoir, located on the North Branch, is a major component of the Baltimore city water system. Patapsco Valley State Park extends along of the Patapsco and its branches, encompassing a total of in five different areas. The river cuts a gorge 100–200 feet (35–70 m) deep within the park, which features rocky cliffs and tributary waterfalls. Bloede's Dam, a hydroelectric dam built in 1906, was located on the