In 1848, there were about 4,000 Spanish-speaking people in today's California on the American side. (Today the state has a total of nearly 40,000,000 people.) In 1849, gold was suddenly found and the number of people went up very fast as the Gold Rush took hold. Slavery also spread there as people hoping to find gold brought black slaves and either forced them to work in gold mines or hired them out for other work. In 1850, California became a state in the Union (the United States).