<Li> One motive for the Gadsden Purchase of land from Mexico in 1853 was to obtain suitable terrain for a southern transcontinental railroad, as the southern portion of the Mexican Cession was too mountainous . The Southern Pacific Railroad was completed in 1881 . </Li> <Li> The Pacific Railroad Act of 1862 (based on an earlier bill in 1856) authorized land grants for new lines that would "aid in the construction of a railroad and telegraph line from the Missouri river to the Pacific ocean". </Li> <Li> The rails of the "First Transcontinental Railroad" were joined on May 10, 1869, with the ceremonial driving of the "Last Spike" at Promontory Summit, Utah, after track was laid over a 2,826 km (1,756 mi) gap between Sacramento and Omaha, Nebraska / Council Bluffs, Iowa in six years by the Union Pacific Railroad and Central Pacific Railroad . Although through train service was in operation as of that date, the road was not deemed to have been officially "completed" until November 6, 1869 . (A physical connection between Omaha, Nebraska, and the statutory Eastern terminus of the Pacific road at Council Bluffs, Iowa, located immediately across the Missouri River was also not finally established until the opening of UPRR railroad bridge across the river on March 25, 1873, prior to which transfers were made by ferry operated by the Council Bluffs & Nebraska Ferry Company .) </Li> <Li> The first permanent, continuous line of railroad track from coast to coast was completed 15 months later on August 15, 1870, by the Kansas Pacific Railroad near its crossing of Comanche Creek at Strasburg, Colorado . This route connected to the eastern rail network via the Hannibal Bridge across the Missouri River at Kansas City completed June 30, 1869, passed through Denver, Colorado, and north to the Union Pacific Railroad at Cheyenne, Wyoming, making it theoretically possible for the first time to board a train at Jersey City, New Jersey, travel entirely by rail, and step down at the Alameda Wharf on San Francisco Bay . This distinction existed until March 25, 1873, when the Union Pacific Missouri River Bridge at Omaha was opened . </Li>

Where did the western and eastern lines of railroad finally meet