Most of the early Chinese immigration to the United States can be traced to the mid-1800s. These early immigrants—some 25,000 in the 1850s alone—came seeking economic opportunity in America. The Chinese arriving in San Francisco, who came primarily from the Taishan and Zhongshan regions as well as Guangdong province of mainland China, did so at the height of the California Gold Rush, and many worked in the mines scattered throughout the northern part of the state. Others took jobs as farmhands or in the burgeoning garment industry in the “City by the Bay.” Still more became laborers with the Central Pacific and Transcontinental railroads, and were instrumental in building the transportation infrastructure that helped fuel the westward expansion of the United States before, during, and after the Civil War.