The rapid growth of the population of San Francisco started in 1848. The main reason was the California gold rush. The gold was found in the Sierra Navada and it brought many people to California from the rest of the US and abroad. The population boom included many workers from China. The population of San Francisco increased from about 20,000 in 1850 to about 150,000 in 1870. Answer: C. Discovery of gold in the Sierra Nevada.
