No scouring the Internet for a reference here; the novel does the work for you when Lee reads from the Book of Genesis:
"And Cain went out from the presence of the Lord and dwelt in the land of Nod on the east of Eden." (22.4.30)
First of all, Nod sounds like a really boring place. Second of all, nobody wants to be to the east of Eden, now do they? They want to be in Eden. What's the point of just living next door to? So east of Eden, as a turn of phrase, is really about the fact that Cain has been kicked out of Eden, and now has to somehow figure out how to survive in the cruel, mean world.
But if Nod is in the east, that implies that Eden is in the west. This is where things get a little complicated. Adam, who starts out in Connecticut, goes west to California to make his Eden in Salinas. So far, so good. But then it's not like the action ever moves east again. The east is more metaphorical.
Yet at the same time, there is definitely an east-west contrast permeating the book: we've got the eastern versus the western United States, and we've also got the East, as in the Orient, as in China, as in where Lee is supposedly from (but really not) versus the West, as in Western civilization, as in Europe and Christianity and all that jazz, which Samuel does a pretty good job of embodying.
Our point is, there are a lot of ways to think about how east and west are at work in the novel, and you should totally go read about contrasting regions in the "Themes" section for more.