October 6, 1866
Union Pacific Crews Pass 100th Meridian
Union Pacific crews reached an important milestone when they passed the 100th meridian near Cozad, Neb. This guaranteed the railroad the irrevocable right to continue westward, as stipulated in the Pacific Railway Act of 1862. Thomas Durant hosted a "100th Meridian Excursion," organizing on the spot a group of reporters and politicians to note the event. In 1879, the U.S. Geological Survey officially established the 100th Meridian to mark 100 degrees of longitude west of Greenwich as the boundary between the "moist east and the arid west."