For nearly five decades, the Southern Pacific Railroad utilized two massive roundhouses at its railyard near downtown Tracy. The roundhouses were constructed to service and repair steam locomotives at Tracy, which was a major waypoint on the SP during the first half of the Twentieth Century.

A view of the SP’s Tracy turntable, looking between the old roundhouses, circa early 1950s.
In the mid-1950s, the Southern Pacific began the complete phase-out of steam locomotives, replacing their entire fleet with more reliable diesel-electric locomotives, which required substantially less maintenance.