Gold Rush: A period in history marked by rapid migration of people in search of gold; specifically, the California Gold Rush occurred from 1848-1855.
Prospecting: The act of exploring an area in search of mineral deposits or oil. In this case, prospecting refers to searching for gold.
Migration: The movement from one region or country to another. This term is relevant because it describes the mass movement of people (like the '49ers) towards areas with perceived opportunities.