The California Gold Rush (1848–1855) was a gold rush in California, which began on January 24, 1848, when gold was discovered by James W. Marshall at Sutter's Mill in Coloma, California. The news of gold brought approximately 300,000 people from the rest of the United States and abroad to California, which had recently been conquered from Mexico. The gold-seekers were nicknamed "forty-niners", referring to 1849, the peak year for gold rush immigration.

Source: Wikipedia