Mopping The Sidewalk

So the weather has been nice for all a while now so I have been out walking a lot and exploring all those areas that aren't close to parking.  Many of the sidewalks along some of the major streets are marble, especially  in front of major stores and shopping centers.  Anytime I've been by they have always been very clean and shiny and frankly I hadn't really put any thought into it.  It rarely rains here, so they don't get a good cleaning the natural way, they have to clean them, right?  So I'm walking outside down the street today and they are MOPPING the sidewalks!  It makes sense if you think about it, it just struck me as very funny!