Portland is the only city in the United States that owns operating mainline steam locomotives, donated to the city in 1958 by the railroads that ran them. Spokane, Portland & Seattle 700 and the world-famous Southern Pacific 4449 can be seen several times a year pulling a special excursion train, either locally or on an extended trip. The "Holiday Express", pulled over the tracks of the Oregon Pacific Railroad on weekends in December, has become a Portland tradition over its several years running. These trains and others are operated by volunteers of the Oregon Rail Heritage Foundation, an amalgamation of rail preservation groups which collaborated on the finance and construction of the Oregon Rail Heritage Center, a permanent and publicly accessible home for the locomotives, which opened in 2012 adjacent to OMSI.