The valley of ashes is a virtual wasteland of the industrial products produced in New York City. Alluding to the poem by T. S. Eliot, "The Wasteland," in which places and people seem dead spiritually and symbolically. F. Scott Fitzgerald, who greatly admired the poet, connotes this same spiritual death in his description of the billboard of Doctor T. J. Eckleburg, whose dimmed eyes, faded by repeated rains and sunny days, "brood on over the solemn dumping ground."
This "solemn dumping ground" is symbolic of the lives of material and spiritual waste characteristic of many on the East Coast of the United States. Much like his narrator Nick Carraway, Fitzgerald found the affluent Easterners jaded in their love of materialism and their excesses and amorality in the setting of 1922. [Please note that this novel was published in 1925, so it does not and could not have the Great Depression as its subject since the Depression came in 1929 with the Crash of the Stock Market]
The eyes of Doctor T. J. Eckleburg [that] look out of no face but, instead, from a pair of enormous yellow spectacles which pass over a nonexistent nose
are certainly symbolic of the lack of godliness in the Roaring Twenties. The imagery of eyes made dim by many suns looking over the grey wasteland suggests the loss of spirituality in people, especially since the spectacles are yellow, a color often associated with evil. Here, too, in the context of this novel, yellow and gold are often associated with money, as well.
"The certain desolate area of land" alluded to in the first sentence can, therefore, be symbolic of the lack of morality in the characters of this novel: Jordan Baker, who has cheated to win her first gold tournament and bends the truth constantly; Tom Buchanan, who has a mistress; Daisy, who shamelessly kisses Gatsby while her husband is out of the room and who leads Gatsby to think that she will leave Tom while she carries on her affair with him; Meyer Wolfscheim, a bootlegger and member of organized crime and one who has cheated on the World Series, an institution of Americana; Kilspringer, a freeloader who stays at Gatsby's as long as his host permits; and even Gatsby himself as he acquires his wealth illegally and reinvents himself.
The valley of ashes is a location that is described first in Chapter II, and is also the location where the Wilsons live, who are shown to survive a very different kind of existence from the kind of lives that Daisy and Tom Buchanan lead. Throughout the novel, the valley of ashes is shown to represent the graveyard of the American materialism, the other side of America that people such as the Wilsons are consigned to, representing poverty and lives of quiet despair. Note how the valley of ashes is first described:
This is a vally of ashes--a fantastic farm where ashes grow like wheat into ridges and hills and grotesque gardens, where ashes take the forms of houses and chimneys and rising smoke and, finally, with a transcendent effort, of ash-grey men, who move dimly and already crumbling through the powdery air.
The way in which the ashes are symbolic is highlighted through their permeation into everything, even into the forms of living people. Ashes are clearly symbolic of something that is burnt out and of which nothing of value remains, and in the context of this novel, they are symbolic of the failed materialism and spirituality. The reference to the ash-grey men paints a very different side of America than that of the wealthy elite who reveled in the "Roaring Twenties"; it focuses on the America in which many people, including the Wilsons, struggle to make ends meet and live lives of difficult toil and struggle.