Annexation and the Gold Rush

John C. Frémont, a U.S. Army officer, led a scientific expedition to California in 1844. In 1846, on a second trip, he encouraged the American ranchers in the north to revolt against Mexican rule. They seized Sonoma and proclaimed a republic. Meanwhile, the Mexican War had started, and an American naval squadron soon seized Monterey. The north was quickly taken; the south fell to American forces under General Stephen W. Kearny and Commodore Robert F. Stockton in 1847. Mexico ceded California to the United States under the terms of the Treaty of Guadalupe Hidalgo, 1848, which ended the Mexican War.

In that year, gold was discovered by James Marshall at Sutter's Mill, located in what is now El Dorado County. By 1849, prospectors from all parts of the United States and from many foreign countries were rushing to northern California. Many of the “Forty-niners,” as the prospectors were called, arrived with exaggerated expectations of gaining easy wealth, but the reality was that few miners became rich. Nonetheless, the population continued to grow, increasing in two years from about 20,000 to more than 90,000, as immigrants were lured by the fertile soil and pleasant climate. California became a state in 1850, and in 1854 Sacramento was made the capital.