California was the site of the famed gold rush that began in 1849, following the discovery of gold at Sutter's Mill in January of that year. This massive influx of prospectors, known as "forty-niners," drastically accelerated California's population growth and economic development. Towns sprang up almost overnight, and the promise of wealth fueled westward expansion in the United States. The gold rush significantly impacted the state's demographics, culture, and infrastructure, leading to its eventual admission to the Union in 1850 and contributing to the broader narrative of American Manifest Destiny.