James Marshall discovered gold at Sutter's Mill in 1848, sparking the California Gold Rush that lasted from 1848 to 1855. Word of the discovery spread quickly despite efforts to keep it quiet, with thousands of prospectors flocking to California in search of wealth. The population of California ballooned from 15,000 to over 150,000 as people abandoned their homes for the gold fields, transforming California from a territory into a state. While most prospectors found little gold and wealth, the Gold Rush had a profound and lasting impact on California's development.