He explained why non-pressurized planes were expected to route around the mountains, not over them: “All transcontinental air travel of that era, starting with air mail service in the 1920s, was routed through the gap in the Rocky Mountain chain that exists between the Snowy Range and the Wind River Range to the north. This is the same gap, the Great South Pass, that was used by all the historic trails, the Union Pacific Railroad and the Lincoln Highway to cross the Continental Divide.”