Southern Pacific 1673, Steam locomotive at Southern Arizona Transportation Museum, Tucson, United States.

Southern Pacific 1673 is a Mogul-type locomotive with a 2-6-0 wheel arrangement built in the early 1900s, now positioned at the museum's entrance. The restored engine displays the engineering features typical of that period.

Built in November 1900 by the Schenectady Locomotive Works, No. 1673 was based in Tucson by early 1901 and hauled freight across southern Arizona, reaching Nogales, Yuma, Benson, Patagonia, Elgin, Fort Huachuca and Tombstone, logging over a million miles. Relegated to yard switching by the early 1950s, it starred in the 1955 film Oklahoma and pulled a 75th-anniversary excursion from the Southern Pacific Depot that March, after which the railroad presented it to the city of Tucson.

The locomotive appeared in a 1955 film before Southern Pacific donated it to Tucson, marking when it transitioned from active railroad service to historical preservation.

The locomotive stands outdoors beside the Southern Pacific Depot in downtown Tucson, under a shelter with a security fence, and can be viewed from outside at any time. The Southern Arizona Transportation Museum, which cares for the engine, is at 414 North Toole Avenue; the depot restoration was completed and the locomotive reopened to public display on March 20, 2005.

In 1905 the engine was converted from coal to oil, and the 1922 Sacramento rebuild added a superheater in the smokebox, which required changing slide valves to piston valves. The locomotive also carried a Vanderbilt tender until the early 1950s, when a smaller squarebox tender replaced it.