California's formal entry into the United States of America occurred on September 9, 1850. Settled by the Spanish and mostly ignored by later Mexican rulers, who pictured the state as a sleepy backwater with less than 10,000 occupants, California was given to the United States in 1848 as part of the Treaty of Guadalupe Hidalgo, just as gold was being discovered in the northern part of the state. The earlier independence movement had been initiated by the Californio residents, who were people of mixed Spanish ancestry, born in California (especially descendants of the 18th century Spanish settlers), who identified themselves as Spanish Californians, instead of Mexicans, although Mexico technically ruled the state. Newly-arrived (since about 1845) foreigners joined in the fight for independence, which resulted in the independent Bear Flag Republic being declared shortly before California's admission by the U.S. These two events -- the Gold Rush and Statehood -- dramatically and rapidly changed the face of California life forever, and helped make California the place that it is today!
"California becomes the 31st state in record time"