From Handsome Atlas, a collection of awesome 19th century data visualizations based on US Census data. 

handsomeatlas:

In 1848, there were only 325 Chinese immigrants in America. By 1880, there were 300,000, making up ten percent of the population of California!

This was mostly made possible by the Burlingame Treaty of 1868, which opened up immigration relations between China and America. Not without cause, either: 90% of the workforce for the Central Pacific Railroad was made up of Chinese immigrants.

Population distribution of U.S. by age and sex (1870)