What event led to a significant population increase in California in the late 1840s?

The California Gold Rush was a pivotal event that resulted in a dramatic increase in the state's population during the late 1840s. It began in 1848 when gold was discovered at Sutter's Mill, leading to an influx of prospectors, entrepreneurs, and settlers seeking fortune. This influx of people came from various parts of the United States and around the world, including significant numbers from Asia and Latin America, drawn by the promise of wealth.

As news of the gold discovery spread, thousands of hopeful miners made the arduous journey to California, shifting the demographic landscape significantly. Towns and cities sprang up almost overnight to accommodate the surge in population, fundamentally transforming California's economy and society. This event also played a crucial role in the westward expansion of the United States, leading to California's admission as the 31st state in 1850.

The other options, while significant to California's history, did not directly cause the population boom seen during the Gold Rush. The Spanish-American War occurred later, and the Mexican-American War had effects on land and governance but did not lead to a sudden influx of people like the Gold Rush did. The Transcontinental Railroad, completed in 1869, facilitated travel and trade but came after the Gold Rush