This site lets you peer under layers of current graffiti walls all the way back to 1999. What a great way to show the impermanent nature of tags as part of a larger body of art.
I seriously still can’t believe that cities don’t pay graffiti writers and provide walls for them. So it’s not their favorite aesthetic; it’s still an essential part of the public art movement, it brightens the drab city walls, and some of it gets conceptual. Shake yourselves awake, oh ye admin of the citay! Free art is a great opportunity!
Here’s the progression of work on Capitol, in OLYMPIA (gotta rep):
(SAME WALL) In 2007:
more here: Graffitti Archaeology