▁where ▁the ▁P ied mont ▁and ▁Atlantic ▁Coast al ▁P lain ▁meet ▁in ▁the ▁eastern ▁United ▁States . ▁Much ▁of ▁the ▁Atlantic ▁Se ab o ard ▁fall ▁line ▁passes ▁through ▁areas ▁where ▁no ▁evidence ▁of ▁fault ing ▁is ▁present . ▁ ▁The ▁fall ▁line ▁marks ▁the ▁ge olog ic ▁boundary ▁of ▁hard ▁met am orph osed ▁terrain — the ▁product ▁of ▁the ▁Ta con ic ▁or ogen y — and ▁the ▁sand y , ▁relatively ▁flat ▁out w ash ▁plain ▁of ▁the ▁upper ▁contin ental ▁sh elf , ▁formed ▁of ▁un con sol id ated ▁C ret ace ous ▁and ▁T ert i ary ▁sed iments . ▁Ex amples ▁of ▁the ▁Fall ▁Zone ▁include ▁the ▁Pot om ac ▁River ' s ▁Little ▁F alls ▁and ▁the ▁rap ids ▁in ▁Richmond , ▁Virginia , ▁where ▁the ▁James ▁River ▁falls ▁across ▁a ▁series ▁of ▁rap ids ▁down ▁to ▁the ▁tid al ▁est u ary ▁of ▁the ▁James ▁River . ▁Columbia , ▁South ▁Carolina ▁is ▁similar ▁as ▁well ▁with ▁the ▁Cong are e ▁River . ▁ ▁Before ▁navigation ▁improvements ▁such ▁as ▁lo cks , ▁the ▁fall ▁line ▁was ▁often ▁the ▁head ▁of ▁navigation ▁on ▁rivers ▁due ▁to ▁rap ids ▁and ▁water falls , ▁such ▁as ▁the ▁Little ▁F alls ▁of ▁the ▁Pot om ac ▁River . ▁N umer ous ▁cities ▁were ▁founded ▁at ▁the ▁intersection ▁of ▁rivers ▁and ▁the ▁fall ▁line . ▁U . S . ▁Route ▁ 1 ▁links ▁many ▁of ▁the ▁fall ▁line ▁cities . ▁ ▁Canada ▁Montreal ▁( St . ▁Lawrence ▁River ).