Library of Congress, By M. Amelia Raines, Reference Librarian, Geography and Map Division: “Many of the most important cities in the eastern United States owe much of their history to a geological phenomenon which began 250 million years ago. The results of the processes which shaped the Earth itself can be seen on modern maps – not just geological maps, but topographic, political, and even highway maps. Geology North America, like every landmass, is made up of physiographic provinces – regions of land with characteristic geology, morphology, soils, and other environmental features. All through the eastern United States, from New Jersey to Alabama, runs a line where two of these provinces – the Atlantic Coastal Plain and the Piedmont – meet. The Piedmont – essentially the foothills of the Appalachian mountain range – is made up of undulating belts of metamorphic rocks running northeast-southwest. The geology here is complex, and produces a landscape of gently rolling hills. The Atlantic Coastal Plain, by contrast, is flat and sandy. Over millennia, rivers have deposited Appalachian sediments in an alluvial plain stretching from Texas to Cape Cod. Where these two regions meet, elevation drops…and the landscape changes. This line of transition is called the Atlantic Seaboard Fall Line.”