On April 4, 1934, it was an internal combustion locomotive causing a stir with people flocking to see the first streamliner, the Union Pacific M-10000 as it passed through Idaho on its nationwide promotional tour. All along the route from Pocatello to Idaho Falls people stopped to watch the locomotive zip by at 85 miles per hour. Several car drivers raced to try keeping up with the engine on the parallel US 91-191. Bands came out to play for the train in Blackfoot and Shelley.
W. Averell Harriman—who would later develop the Sun Valley Resort for Union Pacific—had the train built, incorporating the best ideas of aeronautical design and the latest railroad technology. It was built with lightweight tubular aluminum construction and was powered by a spark-ignition distillate engine, using a lightweight fuel something like kerosene. It could reach speeds up to 110 MPH.
The M-10000 wasn’t just a prototype, although a second one never was built. The engine was put into service and operated almost a million miles under the name City of Salina before being retired, cut to pieces and recycled for the war effort in 1942.