The California Gold Rush (1848–1855) led to a massive influx of people from around the world, significantly altering the demographic makeup of California.

The discovery of gold at Sutter's Mill in 1848 triggered the California Gold Rush, attracting hundreds of thousands of prospectors, settlers, and entrepreneurs from across the United States and other countries, including China, Mexico, and Europe. This rapid population growth transformed California from a sparsely populated region into a bustling hub of economic activity. The Gold Rush also accelerated California's admission into the United States as a state in 1850 and contributed to the displacement of Native American populations, alongside social and cultural shifts that shaped the region's identity.