The California Gold Rush was one of the greatest catalysts of westward expansion in the United States. Before it began in 1849, California was a sparsely settled region at the far end of the frontier. When the United States annexed this territory from Mexico in 1848, the non-native population of California numbered less than 1,000 people. By the end of the following year, that had risen to 100,000. This marks the fastest rate of population increase in the country's history.

The discovery of gold led to the rapid creation of boomtowns, the growth of San Fransicso into a major port city, and the expansion of the railroad. In just a few decades after the initial gold rush, California became a huge economic center for the country.

The Gold Rush led to greater ethnic and racial diversification in the United States. Thousands of Chinese, Mexican, Polynesian, Filipino, and South American immigrants took part. In addition to all the European Americans and African Americans from the east who flocked to the region, California quickly became one of the most diverse parts of the country.

The California Gold Rush also impacted gender dynamics in the country. Most of the 49ers were men. When they left their families in the east to head to California, the remaining women became responsible for managing the family's affairs. Thousands of women became the head of the household, running their farm or business while their husbands and fathers were panning for gold in the California Sierras.

The Gold Rush even helped to usher in the Civil War. The quick surge in population allowed California to petition for statehood in 1850. That year, a compromise in Congress allowed California to enter the Union as a free state while the matter would be left to popular sovereignty in Utah and New Mexico. This upset the delicate balance between slave and free interests in the country. As a result, supporters of the expansion of slavery felt their interests were under threat, increasing overall tensions.