The great California gold rush began on January 24, 1848, when James W. Marshall discovered a gold nugget in the American River while constructing a sawmill for John Sutter, a Sacramento agriculturalist. News of Marshall’s discovery caused the large influx of “’49ers,” as the gold prospectors were known. California’s overall population growth was so swift that it was incorporated into the Union as the 31st state in 1850—just two years after the United States had acquired it from Mexico.

One of the migrations stimulated by the discovery of gold was the internal westward movement of Americans from the eastern states who hoped to make fortunes in California. At first, there were only two routes. The first entailed a six-month sea voyage from New York around the tip of South America to San Diego or San Francisco. Rampant seasickness, bug-infested food, boredom, and high expense made this route unattractive for many would-be prospectors. The second route brought travelers over the Oregon-California Trail in covered wagons—over rugged terrain and hostile territory. This journey also averaged six months’ duration. By 1850, the length and difficulty of both routes had inspired the construction of the Panama Railway, the world’s first transcontinental railroad. Built across the isthmus of Panama by private American companies to speed travel to California, the railroad helped to shave months off of the long voyage around South America.

In addition to massive emigration from the eastern US, the California gold rush triggered a global emigration of ambitious fortune-seekers from China, Germany, Chile, Mexico, Ireland, Turkey, and France. The number of Chinese gold-seekers was particularly large. The influx of Chinese and other foreign laborers led to ethnic tensions in California, especially as gold grew scarce. Despite the ethnic tensions it engendered, the Gold Rush forever changed the demographic face of California by making it one of the most ethnically diverse states in the Union by the middle of the 19th century.

Reference:

http://www.mapsofworld.com/on-this-day/december-5-1408-the-golden-horde-marches-into-moscow

http://ocp.hul.harvard.edu/immigration/goldrush.html