When did the first transcontinental railroad begin operation?

The First Transcontinental Railroad in the United States was built across North America in the 1860s, linking the railway network of the Eastern United States with California on the Pacific coast. Ceremonially completed on May 10, 1869, at the famous "golden spike" event at Promontory Summit, Utah, it created a nation-wide mechanized transportation network that revolutionized the population and economy of the American West. This network caused the wagon trains of previous decades to become obsolete, exchanging it for a modern transportation system. Authorized by the Pacific Railway Act of 1862 and heavily backed by the federal government, it was the culmination of a decades-long movement to build such a line and was one of the crowning achievements of the presidency of Abraham Lincoln, completed four years after his death. The building of the railway required enormous feats of engineering and labor in the crossing of plains and high mountains by the Union Pacific Railroad and Central Pacific Railroad, the two privately chartered federally backed enterprises that built the line westward and eastward respectively.