What significant event led to nearly 250,000 people migrating to California between 1849 and 1852?

The event that led to nearly 250,000 people migrating to California between 1849 and 1852 is the California Gold Rush. This migration was triggered by the discovery of gold at Sutter's Mill in 1848, which ignited a massive influx of individuals seeking fortune and a new life in the West. The promise of wealth drew not only Americans from various regions but also immigrants from other countries. This period marked a pivotal moment in American history, as it significantly contributed to the population growth and economic development of California, ultimately leading to its admission as a state in 1850. The California Gold Rush reshaped the demographics and socio-economic landscape of the region, making it a key event in the westward expansion of the United States.