Built in November 1941 by the American Locomotive Company (ALCO) as a 4-8-8-4 Big Boy Steam Locomotive.  It was built for the Union Pacific Railroad (UP) and delivered to them in December 1941.  In 1959, after traveling 1,031,205 miles on revenue service with the UP, the locomotive was retired.  In December 1961, the UP donated it to the Southern California Chapter of the Railway And Locomotive Historical Society for display at their RailGiants Train Museum at the Pomona Fairplex in Pomona, CA.  It arrived at the RailGiants Train Museum on January 8th, 1962.  52 years later (June 2013), the Union Pacific Railroad reacquired the locomotive for operation.  On Sunday, January 26th, 2014, at 2:45 AM, the Big Boy departed the Pomona Fairplex for Cheyenne, Wyoming, the base for Union Pacific Steam Program.  Along the way, it made many stops in towns for people to see the Big Boy.  It arrived at the UP Steam Program's shops in Cheyenne, Wyoming, on May 8, 2014.  After arriving in Cheyenne it sat idle for two years inside the Steam Shop Roundhouse.  In August 2016, restoration began.  It took almost three years to restore the Big Boy back to operating status.  In May 2019 it returned to service.

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It is seen here in Casa Grande, Arizona, preparing to leave for Tucson. AZ.