The construction of the Washington Monument was stopped during the Civil War, and when it was resumed later, a slightly lighter shade of stone was used. This resulted in a noticeable line between the darker stone and the lighter stone about 100 feet up the monument. I always tell visitors that the line is the high water mark from the 1936 flood.
Seriously though, D.C. is between 300-400 feet above sea level, so I think the only city that has passed a tipping point is San Francisco from where all this nonsense emanates -- but we knew that already.
Nothing worthy to save in Washington D.C except the US Constitution as for San Fransicko the only thing worth saving is their Sour Dough Bread, Gheridelli Chocolate and the 49ers [ducks] =]