<P> 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 . </P>
<P> 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 . </P>
what discovery set off a massive migration to california
what discovery set off a massive migration to california
gold
gold