The Valley of Ashes is on the way to New York City from West Egg. It has a train track that go through it. Workers shovel out the ashes from the train cars. It is "bounded on one side by a small foul river" with a second railroad track that runs alongside and across the drawbridge over the foul river. When the drawbridge is raised to allow barge traffic to pass, passengers look down on the Valley while the train is stopped. It is literally a stretch of land that has industrial ashes dumped there. The dark imagery helps to create symbols of the plight of the poor as well as the emptiness of of the quest for happiness with riches for the upper class.
The Valley of Ashes is in between the East and West Egg. It is the palce where the "poor" or hardworking people at that time lived.