High Quality Content by WIKIPEDIA articles! Promontory in Box Elder County, Utah, United States, is notable as the location of Promontory Summit where the United States' first Transcontinental Railroad was officially completed on May 10, 1869. It is at an elevation of 1494 meters (4902 ft) above sea level. Promontory is 51 km (32 mi) west of Brigham City, Utah and 107 km (66 mi) northwest of Salt Lake City, and north of the Great Salt Lake. In May 1869, the railheads of the Union Pacific and Central Pacific railroads finally met at Promontory Summit. The ceremony to drive in the Last Spike was originally to be held on May 8, but was postponed two days because of bad weather and a labor dispute on the Union Pacific side.