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Because of waterfalls the Potomac River is not navigable by boat west of Georgetown (Washington, DC).  So in 1828 the C & O canal was dug along the Maryland side of the Potomac.  By 1850 the canal had reached 185 miles to Cumberland, MD, but in the 22 years it took to build, railroads had started to be built and actually beat the canal to Cumberland by 8 years.  Cumberland was a coal mining area and coal was the main cargo to go down the canal.  Mules would walk a tow path that was located between the canal and the Potomac, pulling the boats. There were 72 locks along the 185 mile canal.  The mines were mined out by 1920 and the canal closed in 1924 after a damaging flood.
Today the canal is a national park and you can cycle the towpath.  The canal is missing in a few sections, but is there in most of the park.  In some sections there are aqueducts where the canal goes over a creek that empties into the Potomac.  At the start of the towpath in Cumberland is a museum about the canal and Cumberland.  I cycled the towpath for several miles with my mountain bike as the path is not paved but is crushed gravel.  Since the canal and land between the Potomac and the tow path is national park, nature has taken over with birds and other animals numerous among the many trees.  Tow groundhogs watched me pass, but ran away when  I stopped to chat. In the other direction from the museum there is a bike trail following a railroad northwest  through the Allegany mountains 150 miles to Pittsburgh.  I cycled that trail for several miles also.