Answer:
C: The Gold Rush of 1849; it led to a rapid increase in prospectors migrating into the state.
Step-by-step explanation:
The Mexican defeat in the American Intervention in Mexico forced the Mexican government by the Treaty of Guadalupe Hidalgo to cede California to the United States, along with the other Interior Provinces, in 1848. That same year gold was discovered in California, more precisely in one place called Coloma within the ejido of Sutter's Mill (Mill of Suter), present Sacramento, and many people came to the new US territory to look for gold and try their luck. In a few years, the 4,000 inhabitants had to assimilate the strong immigration.
California officially became a state in 1850 and since then the capital was located in Sacramento, replacing Monterrey. The entry of California into the union was very controversial due to the political imbalance that caused the entry of a non-slave state into the country. For some time the idea of dividing the state into two was supported: one slave and one "free." As happened with Texas and New Mexico when they were transformed into territories (and quite later states), their territories were divided among new ones, for example with parts of California, Nevada and part of Arizona were created (this without counting the territories already ceded before 1825).
The state benefited from the impact of the discovery of gold, but that did not calm local tensions. The presidential elections of 1850 demonstrated the state division, since three candidates divided the votes, winning Abraham Lincoln the state with only 32% of the votes. The stage was ready for a war between the political and social forces of the United States.