why did americans move west in the years following the civil war?

Why did americans move west in the years following the civil war?
The Americans moved west because the most precious metal,gold,was discovered there.This is called gold rush in the history.
A gold rush is a period of feverish migration of workers to an area that has had a dramatic discovery of gold deposits.
Gold rushes were typically marked by a general buoyant feeling of a "free for all" in income mobility,in which any single individual might become abundantly wealthy almost instantly,as expressed in the California Dream.
Gold rushes helped spur a huge immigration that often led to permanent settlement of new regions and define a significant part of the culture of the Australian and North American frontiers.As well,at a time when the world's money supply was based on gold,the newly-mined gold provided economic stimulus far beyond the gold fields.