Union Pacific No. 3105 is an SD40-2C type diesel locomotive built by Electro-Motive Diesel (EMD) in June 1979, originally for the Missouri Pacific Railroad (MP) as their No. 6027. When the MP was acquired by the Union Pacific Railroad (UP) on January 1, 1997, it was renumbered to UP 3105. It served in regular freight service with the UP until January 2014 when it was traded to the RailGiants Train Museum in Pomona, CA in exchange for UP Big Boy No. 4014 for its restoration to operating condition by the UP for excursion service. It later arrived at the museum on February 22, 2014 along with a UP boxcar and a UP caboose where it has remained mostly on static display ever since.
It is the first and only operational piece of rolling stock at the museum and occasionally still operates on the museum grounds from time to time.