The Willets Point location has historical significance on several levels:
The town of Flushing was first settled in 1645 under charter of the Dutch West India Company.... By the 1850s, a second crossing, Strong's Causeway was built near the present-day Long Island Expressway, extending Corona Avenue towards Flushing. This crossing was located near the confluence of Horse Brook and the Flushing River. In the mid-19th Century, the growing city of Brooklyn gave the land around the river to the Brooklyn Ash Removal Company, which turned the salt marshes into landfill. The pollution was chronicled by F. Scott Fitzgerald in The Great Gatsby, where Jay Gatsby observed the "valley of ashes" on his train ride between Manhattan and Long Island. In 1936, Robert Moses proposed closing the ash landfill and transforming it into a park through its use as a World Fair site. With the exception of the Willets Point triangle, the landfill was leveled, the riverbed was straightened, and the southern part of the river was deepened to form the Meadow and Willow lakes. --
Wikipedia
In the Great Gatsby: CHAPTER II
The opening description of the valley of ashes, watched over by the brooding eyes of Dr. T. J. Eckleburg, has been analyzed again and again. Fitzgerald's friend and editor, Maxwell Perkins, wrote to Scott on November 20, 1924: "In the eyes of Dr. Eckleburg various readers will see different significances; but their presence gives a superb touch to the whole thing: great unblinking eyes, expressionless, looking down upon the human scene. It's magnificent." Later in the same letter Perkins concludes, "...with the help of T. J. Eckleburg... you have imported a sort of sense of eternity."
How should you approach this famous symbol? Remember, a wide variety of interpretations have been made and defended over the years.
It's best to begin by placing Eckleburg in his geographical context: the valley of ashes, located about halfway between West Egg and New York City. The valley of ashes is the home of George and Myrtle Wilson, whom we'll meet later on in this chapter. The valley is also a very important part of what we might call the moral geography of the novel. Values are associated with places. In Chapter I we were introduced to East and West Egg, the homes of the very rich, the nouveau riche, and the middle class. The valley of ashes is the home of the poor, the victims of those who live in either New York or the Eggs. M en, described by Fitzgerald as "ash-gray," move through the landscape "dimly and already crumbling through the powdery air."
-- From CliffNotes