The Fall Line is a geological and hydrological phenomenon that has greatly affected the course of urban development in the eastern United States. It is an imaginary line drawn through the point in eastern rivers where a change in elevation, and the resulting waterfall, makes navigation further inland from the Atlantic impossible. Canals with hydraulic locks are often found at these fall line navigational obstructions. Cities also usually can be found at the fall line, as they are generally sites of offloading and transfer of commercial goods to points further up- or downstream, eventually becoming social loci supporting this commercial activity. Prominent "fall line cities" include Richmond, Virginia, Columbia, South Carolina, Augusta, Georgia, and Lowell, Massachusetts. Because of the change in elevation, these cities often became sites of hydropower development and contained factories, such as textile mills, which were driven by water power.