Virginia Key Park in Miami, FL was built on a landfill, and Santos in Ocala, FL was built on the site of a failed canal project. In fact, most Florida trails are built on the sites of failed or decommissioned public works projects!
Laurel Hill trail system, Lorton Va is built on what was a large prison complex. Trails are named after whatever part of the complex they were built on: Slaughterhouse, Dairy Barn, Power Station, Apple Orchard, Workhouse. Very nice suburban DC trail system.
If we’re including mining land, there’s a lot–Five Points in North Georgia, which we rode Jeff, was built on old mining tailings.
I’m not sure if this fits, but Jungle Habitat is a trail in New Jersey that was built on the site of an abandoned wild life amusement park–pretty unique trail: http://www.singletracks.com/bike-trails/jungle-habitat.html
Wildlife Prairie Park – Peoria IL. Old Strip Mine (Coal) – in the home of Caterpillar which made for a pretty massive mining operation, mining ceased 30+ years ago. Maybe the fastest, flowiest, single track this side of Boca Raton FL? In all seriousness, it’s an awesome trail system, and only one of seven in the immediate area.