Which event in 1848 contributed to California's rapid population growth?

The establishment of the Gold Rush at Sutter's Mill in 1848 was pivotal for California's rapid population growth. When James Marshall discovered gold at Sutter’s Mill, news spread quickly across the United States and even internationally. This discovery ignited a massive influx of people, known as "Forty-Niners," who traveled to California hoping to strike it rich. The Gold Rush dramatically transformed California from a sparsely populated area into a bustling hub of migration and settlement.

The associated economic opportunities, rapid urbanization, and the establishment of towns and mining camps helped shape California's demographic landscape. By the end of the Gold Rush, California's population soared, contributing to its eventual statehood in 1850.

In contrast, while other events like the construction of the transcontinental railroad, the signing of the Treaty of Guadalupe Hidalgo, and the discovery of silver in Nevada played important roles in California's development, none had the immediate and intense impact on population growth as the Gold Rush.