Potholes in my Street

One side-effect of all this rain we're having in Los Angeles that no one ever mentions is the gigantic potholes that have suddenly appeared everywhere. How does this happen? I get the houses sliding down hills and pools caving in and trees falling over -- that all makes sense. The cause-and-effect relationship between heavy rain and these hazards is easy to see. But potholes? Was it raining rocks? Or some other hard objects that would tear up the streets? I am confused.

That's all. There's no point to this other than I don't get it.