Major cities on the west coast are also full of old tunnels. Some are tourist attractions now. Goes back to the old days of kidnapping drunks to work on the ships, so I've read. Who knows how many networks of tunnels are under cities that are not on the tourist tours. I know of a few smaller cities in western states that also have networks of old tunnels that are quite a bit inland. Not sure what they were originally for but I know they were not in mining areas.
I remember seeing a television news special about this. I guess Portland was one of the worst cities for this. One bar had a trap door under a bar chair. One yank on the door, and you were shanghaied. Lots of people went missing during the late 1800's and early 1900's. Most people don't know that there is a whole city under the city.