How do the contrasting values in the landscape affect the reader's sense of the valley in East of Eden?

In East of Eden, John Steinbeck offers a sharp contrast between the areas to the east and west of the Salinas Valley. The Salinas River cuts through the valley, between two different mountain ranges.
On the east side are the Gabilan Mountains. These represent optimism and wholesome qualities of life. They are presented as light-filled and enticing, a warm and lovely setting. A sharply different image applies to the valley’s west side, with the Santa Lucia mountains shown as more negative and physically dark, creating a foreboding, dangerous sensation.
The strongly-drawn contrast corresponds to the lives of the characters who seem caught between those worlds, both within a single generation and passed down from one generation to the next. The good and evil contrasts extend from Adam and his half-brother, Charles, to Adam’s twin sons, Cal and Aron. Likewise, the Trask ranch is located in the most fertile part of the valley, while the Hamilton ranch is stuck in a dry, unproductive area.