Because the soil was depleted during the time of the dust bowl many people:

Moved westward to coastal states, is the right answer.

Explanation:

The Southern Plains experienced severe drought throughout the 1930's. Due to this relentless dust storms occurred that destroyed the ecology and farming of the prairies of America and Canada. Due to such climatic conditions, people and livestock died in Texas, Oklahoma and Nebraska. Since agricultural activities could not take place in such an environment thus people chose to move West in search of better living opportunities in the West Coastal region of the nation.