into a deep, narrow wooded gorge. The streamcourse is part of Bluemont Park and then Glencarlyn Park, where it crosses Arlington Boulevard (U.S. 50). The stream exits the gorge into flatter terrain just south of the Columbia Pike crossing. The stream then flows through Barcroft Park, Shirlington Park, and then between Jennie Dean Park and the Shirlington business district. At Shirlington, the Washington & Old Dominion Trail ends as the Four Mile Run Trail continues above the stream's north bank as the waterway becomes the boundary between Arlington and Alexandria. Downstream of Shirlington, the stream is channelized as a flood control measure, although restoration efforts are ongoing. The stream crosses under Interstate 395, and then becomes tidal in the vicinity of the Mt. Vernon Avenue crossing, whereupon its name changes to Four Mile Creek. The creek flows through Four Mile Run Park, and then underneath Richmond Highway (U.S. 1), the WMATA Yellow and Blue Lines, and the George Washington Memorial Parkway before reaching its mouth at the Potomac River at the south end of Ronald Reagan Washington National Airport. History During the colonial period and the 19th century, several watermills existed in and near the fall line of the stream. Although none of these mills remain intact, the foundation of one is still in place (Arlington Mill constructed in 1836; later rebuilt as Barcroft Mill in 1880 after being destroyed by Union Army troops during the Civil War). The mill provided locals with flour ground from corn and wheat that was grown locally and shipped up the stream on flatboats. Located west of the stream between Columbia Pike and 10th Street South in Arlington, the foundation presently supports an automobile repair shop. General George Washington owned on the southwest side of the stream in the fall line a large parcel of wooded property which he surveyed in 1785, several years after the Revolutionary War ended. As part of this survey, Washington made a cut in the trunk of an oak tree to mark a corner of his property where a tributary (Long Branch (upper)) entered the main stream. A portion of this trunk remains preserved in a neighborhood library (Glencarlyn Library), while a columnar monument marks the tree's original location. From about 1860 to 1968, the Washington and Old Dominion Railroad and its predecessors traveled along most of the stream's length in Arlington. The Northern Virginia Regional Park Authority's Washington