With the country continually expanding and growing, Congress passed the Pacific Railroad Acts in 1862, authorizing two companies, the Union Pacific and the Central Pacific, to construct a transcontinental railroad. Work began the next year, and eventually over 18,000 Chinese, German, Irish, and Italian immigrants worked on the project. The last spike was driven on May 10, 1869, in a ceremony at Promontory, Utah.
Memorial and Joint Resolution relative to a grant of Lands, 2/11/1858, Records of the U.S. House of Representatives
Letter from Secretary of the Interior, 1/14/1869, Records of the U.S. Senate