Industrial timbering cleared large swaths of stable old-growth woodland, removing key components of a stable ecosystem, changing the character of the land, and allowing plant growth previously hindered by the dense canopy while creating habitat that supported deer, turkey, bear, and small mammal populations. Some cleared lands were later converted into state forests or game lands. Coal mining dug deep shafts and tunnels below the surface, disrupted groundwater patterns by creating new subsurface channels and pools sometimes harboring acidic chemicals, and concentrated waste materials in large mounds called culm banks or overburden piles. As industry declined, the region was left with abandoned rail corridors, canal ways, underground mines, houses, commercial buildings, disrupted groundwater patterns, culm banks, and deep stripping pits. Some abandoned rail corridors became recreational trails, while abandoned canal ways, commercial buildings, and mining villages became heritage sites. Some large waste piles have been re-mined for waste coal burned to make electricity, and some new underground water pools are used for geothermal heating. The first federal mine reclamation act, passed in 1977 in direct response to major landscape changes caused by mining, required permits and bonds to ensure projects were carried out properly and that money would be available for cleanup and reclamation after mine closure.