Today in train history...

January 12, 1883
The last spike was driven on the Pecos River Bridge in New Mexico, completing the Sunset Route. The Sunset Route is a through line from California to New Orleans, with associated steamer connections to New York. It is the first US route from the Atlantic to the Pacific controlled by a single company, the Central Pacific. The Central Pacific railroad company is also arguably the first US transcontinental railroad company.

Source: California State Railroad Museum