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Fall zones along streams within the Blue Ridge and Piedmont provinces of North Carolina and Virginia are distributed systematically. Nearly all occur along seven curvilinear trends (fall lines) that parallel the regional tectonic fabric and gravitational gradient of the Appalachian orogen. These seven fall lines are defined and named, and the processes that could have formed them are discussed. The limited available evidence favors a neotectonic origin. The fall lines described here probably formed within the last 2 million years, because late Pliocene fluvial terraces that accumulated along major Piedmont riverways appear to be warped in tandem with adjacent fall zones across at least two of these lines. This indicates that the modern fall lines developed in latest Pliocene or Pleistocene time, after the terrace deposits had accumulated. Introduction Although fall zones are an important source of water power in the Piedmont of North Carolina and Virginia, they have been a serious impediment to navigation since the earliest European exploration and settlement. Exploring upstream, colonial era ocean-going ships quickly found their way blocked by major rapids or falls along nearly every major coastal river. These rapids and falls define a prominent linear trace that has been called the "Fall Line" or "Fall Zone" for over a hundred years (for example, Darton, 1894; Clark and others, 1912; Renner, 1927; Dietrich, 1970; Reed, 1981; Hack, 1982; Johnson and others, 1987). This fall line consistently has been located at or near the western edge of the Atlantic Coastal Plain physiographic province (Figure 1, labeled TFL). The origin of "the Fall Line" has been ascribed to tectonic warping (for example, McGee and others, 1891; Hack, 1957; Mixon and Newell, 1977; Reed, 1981), though variation in world eustatic sea level in response to Quaternary glaciation also has played a significant role in shaping its present prominence as a geomorphic feature (Hack, 1957).

u.s. geological survey open file report/open-file report

Newly recognized en echelon fall lines in the Piedmont and Blue Ridge provinces of North Carolina and Virginia; with a discussion of their possible ages and origins