The California Gold Rush included thousands of Mexican and Chinese arrivals. Chinese migrants, many of whom were impoverished peasants, provided the major part of the workforce for the building of the Central Pacific portion of the transcontinental railroad. Most of them went home by 1870 when the railroad was finished. Those who stayed on worked in mining, agriculture, and opened small shops such as groceries, laundries, and restaurants. Hostility against the Chinese remained high in the western states/territories as seen by the Chinese Massacre Cove episode and the Rock Springs massacre. The Chinese were generally forced into self-sufficient "Chinatowns" in cities such as San Francisco, Portland, and Seattle. In Los Angeles, the last major anti-Chinese riot took place in 1871, after which local law enforcement grew stronger. In the late 19th century, Chinatowns were squalid slums known for their vice, prostitution, drugs, and violent battles between "tongs". By the 1930s, however, Chinatowns had become clean, safe and attractive tourist destinations.