The 'valley of ashes' lies between Long Island and New York and the Wilsons live on the edge of this area. It is a desolate industrial wasteland, bounded on one side by "a small foul river".
Fitzgerald uses an agricultural image to stress its barren nature through contrast: "a fantastic farm where ashes grow like wheat into ridges and hills and grotesque gardens". The "spasms of bleak dust" which drift over the area turn everything grey so the men who work on the railroad there are themselves "ash-grey".
The imagery of dust and ashes recalls death – the people who are condemned to live and work there inhabit a kind of living death, shut out from the wealth that more privileged people such as the Buchanans enjoy.
'Ashes' also has connotations of penitence and humiliation. Tom humiliates Wilson both verbally and by his actions - he is having an affair with his wife. Myrtle despises Wilson for his poverty.
As well as revealing the huge gulf between the haves and have-nots in America in the 1920s, in the valley of ashes Fitzgerald also hints at the spiritual barrenness of American society, which is materialistic and lacking in morals or decency. Nick says he always finds the area "vaguely disquieting", reflecting his feelings about the moral decay that it suggests.
George Wilson's garage is a "small block of yellow brick sitting on the edge of the waste land".