It depends on the geography of the area that the city is located in but no matter what the vast majority of that mile is going to be bedrock.

I thought they were just in the sewers under the city or something. Pulling a Fairy Tail universe wizard through a street or layer of rock I can totally see. Pulling a beginner wizard through a noticable portion of the planet's upper layer will give you a hunk of meat. And that's leaving out how difficult such a feat would be in the first place.