The Northwest Branch enters a scenic, rugged rocky gorge at the Fall Line, where the tough metamorphic rocks of the Piedmont give way to the sandy sediments of the Coastal Plain. This rapid change in gradient creates a series of waterfalls in the stream’s “Torrent and Gorge” section; below the Fall Line, the stream widens and slows. As a tributary of the Anacostia River, the Northwest Branch lies within an area whose rugged beauty helped lead Maryland to identify the Anacostia as a Scenic and Wild River in 1984 under the Maryland Scenic and Wild Rivers Act. On larger streams and rivers, the Fall Line generally marks the limit of travel by ships, and many large cities such as Washington, D.C. and Baltimore were established just below this geographical barrier where ports could be established. The steep-sided valley was also a favorite of President Theodore Roosevelt, who praised its beautiful gorge, great boulders, cliffs, and scenery after a ride there with his wife in 1904.