In 1854, John Pope of the US Army (and a veteran of the Mexican American War) was tasked by Secretary of War Jefferson Davis to plot out a transcontinental railroad route through Texas. Southern politicians worked very hard to convince the rest of Washington that a southern, not northern, transcontinental route was preferable.
Pope documented his expedition on this map, which was printed in 1861. He denoted where he set up camps along his journey, which started at the Rio Grande in El Paso and ended at the Red River in Preston (Grayson County, TX). This is a small portion of the much larger map – I especially like where he marked the “lower” and “upper” cross timbers around misspelled Gainesville (Cooke County).
It looks a lot like he didn’t “invent” the trail that he took – in many places, it mirrors the Butterfield Overland Stagecoach route, which suspended operations at the start of the Civil War. Southwest of Fort Belknap (Young County), he surveyed a more westerly direction, as the stagecoach route meandered towards Fort Phantom Hill.
When southern states left the Union in 1860-1861, the hopes for a transcontinental line from St. Louis to San Diego (through Arkansas, Texas, New Mexico, and Arizona) seceded with them.