Substances for ground surfaces.

asphalt_mastic
asphalt_wma_concrete
beach_gravel
beach_sand
beach_sandy_soil
concrete_asphalt_rolled
coral_stone
dry_tiremarks_ground
dune_sand
flagstone
gravel_crushed
gravel_mud
ground_rocky
lava_stone
mud_cracked
pebble_beach
rock_sulphurized
sand_cracked
sand_gravel_soil
sand_ground_damp
sand_muddy_cracked
sand_stone_rock
scorched_forest_ground
soil
soil_cracked
tiretracks_chevron_mud
volcanic_gravel
volcanic_soil
volcanic_soil_muddy
walkway
wood_planks