After the Portolà expedition of 1769 -- 70, Spanish missionaries began setting up 21 California Missions on or near the coast of Alta (Upper) California, beginning in San Diego. During the same period, Spanish military forces built several forts (presidios) and three small towns (pueblos). Two of the pueblos would eventually grow into the cities of Los Angeles and San Jose. After Mexican Independence was won in 1821, California fell under the jurisdiction of the First Mexican Empire. Fearing the influence of the Roman Catholic church over their newly independent nation, the Mexican government closed all of the missions and nationalized the church 's property. They left behind a small "Californio '' (white Hispanic) population of several thousand families, with a few small military garrisons. After the Mexican -- American War of 1846 - 48, Mexico was forced to relinquish any claim to California to the United States. The unexpected discovery of gold in 1849 produced a spectacular gold rush in Northern California, attracting hundreds of thousand of ambitious young men from around the world. Only a few struck it rich, and many returned home disappointed. Most appreciated the other economic opportunities in California, especially in agriculture, and brought their families to join them. California became the 31st US state in 1850 and played a small role in the American Civil War. Chinese immigrants increasingly came under attack from nativists; they were forced out of industry and agriculture and into Chinatowns in the larger cities. As gold petered out, California increasingly became a highly productive agricultural society. The coming of the railroads in 1869 linked its rich economy with the rest of the nation, and attracted a steady stream of migrants. In the late 19th century, Southern California, especially Los Angeles, started to grow rapidly.
what discovery set off a massive migration to california
gold gold gold