Gold has always been one of the most highly valued metals in the world. It is used in the manufacture of everything from jewelry to electronics, and has been established as the basis for monetary systems worldwide. The factor that makes gold valuable is its rarity. Although gold can be found in many different areas, the most valuable deposits are large veins of gold ore running through mountains. When a large deposit is found, mining the deposit greatly boosts the economy in settlements and cities near the mine. Historical examples of this phenomenon are the many towns that grew and prospered over a relatively short time during the California gold rush in America during the 1800s.