What does the title "East of Eden" signify?

Steinbeck's novel East of Eden is a
symbolic retelling of the Cain and Abel story set in the fertile Salinas Valley of
California, and as such the title alludes to the Biblical passage in which
Cain

went out
from the presence of the Lord and dwelt in the land of Nod, east of
Eden.

In the
novel, like God who accepts Abel's gift and rejects that of Cain,  Cyrus Hamilton
rejects a gift from his son Charles, but accepts a lesser one from his son Adam. 
Maddened by this rejection, Charles beats his brother Adam, and then Adam joins the army
in World War I. 

Ironically, the story of Eden is
reiterated in another fashion with Adam and his wife Cathy as a sin-ridden Eve; With
their children, Caleb and Aron, the story of Cain and Abel is retold, as well,
as, ironically, Adam rejects a present from his son Caleb while he accepts the gift from
Aron.  Having been rejected, Caleb, too, rebels and takes Aron to see his prostitute
mother; this event causes disastrous results.