Southern Pacific Railroad 1673 is a standard gauge 2-6-0, Mogul type of the M-4 class, steam locomotive built in 1900 by Schenectady Locomotive Works; the engine was delivered in November of that year, and by early 1901 it was based in Tucson, Arizona and operated primarily in southern Arizona hauling freight trains.

In 1962, the locomotive had to be moved to a display location at Himmel Park in Tucson due to construction at the Historical Society to expand the size of its buildings, which left no room for the engine.

The engine sat for many years there at the park, exposed to the elements and gradually deteriorating, as well as suffering periodic vandalism and theft of equipment, including its builder's plates and gauges.

During one abortive attempt in 1965, the locomotive was steamed up to clear out the whistle, and run a short distance on the display track at Himmel Park.

Although it was determined that restoration to operational condition was feasible, the project was abandoned due to the higher than expected costs related to repairing or replacing its boiler.

In December 2000, the engine was moved out of the park to the Southern Pacific Depot in downtown Tucson, and over the next two years a shelter and security fence were erected around it.

By summer of 2011, work was started on cleaning, relubricating, reassembling and reinstalling on the locomotive parts that were removed during the 1992–1994 restoration, but kept in storage for many years.

Other work includes finding or fabricating suitable replacements for parts lost, stolen, or badly damaged beyond repair over the many years No.