The Garbage mounds are heaps of refuse outside the Factory in the Shadowlands. After Grey Guards reach their fail date, they are dumped in the mound and replaced by a fresh batch of Guards. The Guards in the mounds are decomposing and melting, emitting a stench of decay. They are unable to move and cannot do much but lie in heaps and wait to die.
Expired Guards and detritus from the Factory are placed in the mounds.
Lief, Barda, Jasmine, and Emlis took cover in the mounds when they were pursued by a vraal in the Shadowlands. They did not see what the mounds were made of until a decomposing Guard began speaking, saying he could smell humans nearby. Many of the decaying Guards then tried to seize the companions, but could do nothing in their weakened state. They called out that they had found the girl with the black bird and they could still be useful to their Master.