Promontory Summit is notable as the location where the United States' first Transcontinental Railroad was officially completed on May 10, 1869, with the driving of the Golden Spike, joining the Union Pacific and Central Pacific railroads. Promontory was the site of a temporary city during and shortly after the construction of the railroad, but this was then dismantled, and since then Promontory has had no permanent population. Since 1957 it has been preserved as part of the Golden Spike National Historic Site. Of historical note is that the eastbound and westbound railheads were joined at this location on May 10, 1869. However one final link remained to actually complete coast to coast. Near present day Lathrop, California the Mossdale Crossing bridge had to be completed across the San Joaquin River. The vertical lift drawbridge was not completed until September 1869, at which time the coast to coast link was actually completed. Today Mossdale Crossing is a county park and the site is a California Historical Site with a Marker located at N 37° 47.242 W 121° 18.305.
Although there is no longer a continuous railroad track running through Promontory, Utah, a section of track was relaid for Centennial operations in 1969. Furthermore, the NPS had two exact replicas of the UP #119 and Jupiter #60 built in California in the 1970s. The original engines were scrapped long ago. Both engines operate on a seasonal basis.