A line roughly along Interstate 95 joining areas of relatively steep gradient on several rivers on Maryland's western shore. The line marks the geographical area where each river descends from the hilly Piedmont to the flat and sandy Coastal Plain. It also marks the limit of upstream commercial navigation.
A line connecting the waterfalls of nearly parallel rivers that marks a drop in land level.
A line joining the waterfalls on several rivers that marks the point where each river descends from the upland to the lowland and marks the limit of navigability of each river.