To understand Electromagnetic signals, you need to understand magnetism. Do you know that a magnet will only be attracted by metals? Not wood. Not concrete. Not dirt. Not human flesh.

Metals are found in the Earth. You cannot know what is inside the Earth unless you dig it out or scan it. Because of this, towers need to be placed on top of structures to avoid POTENTIAL metals in the Earth.

Just to be clear:

1. Not all stones affect EM signals. Only metal composites.
2. Towers are placed on top of mountains to avoid POTENTIAL metal composites in the Earth.
3. Concrete, dirt, "modern cascets" do nothing to dull the EM potential of the waves.