| Southern Pacific 5021 | |
| Powertype: | Steam |
| Operator: | Southern Pacific Railroad |
| Fleetnumbers: | SP 5021 |
| Whytetype: | 4-10-2 |
| Cylindercount: | 3 |
| Builder: | American Locomotive Company |
| Builddate: | 1926 |
| Serialnumber: | 66793 |
| Weightondrivers: | 317500lb |
| Driverdiameter: | NaNinches |
| Boilerpressure: | 225psi |
| Cylindersize: | (inside) 25x dia × stroke (outside) 25x dia × stroke |
| Tractiveeffort: | 84200lbf 96540lbf with booster |
| Maxspeed: | 70mph (Passenger Service) |
| Tendercap: | 16152USgal water 4912USgal fuel oil |
| Numinclass: | 49 |
| Operatorclass: | SP-2 |
| Retiredate: | 1955 1963 |
| Restoredate: | 1961 |
| Currentowner: | Railway and Locomotive Historical Society |
| Disposition: | On static display at the RailGiants Train Museum in Pomona, California |
Southern Pacific 5021 is an SP-2 class 4-10-2 steam locomotive built in 1926 by ALCO at their Schenectady, New York, shops. It is the only member of this class of SP locomotives to be preserved, and it is one of only five three-cylinder locomotives preserved in North America.
The locomotive was built in 1926 by Alco. It was designed to haul mixed freight and passenger trains over the Sierra Nevada range between northern California and Nevada. Later in its career, No. 5021 was shifted to service in Oregon, where it remained until its retirement in 1955.
Southern Pacific donated 5021 to the Railway and Locomotive Historical Society on 8 March 1956. In 1961 it was fired up and used for operation on the museum's spur line. However, the Southern Pacific did not like this, so they were forced to pull the tracks in 1963. Following this, 5021 was stored in the roundhouse of the Atchison, Topeka and Santa Fe Railway. While it was stored, a possible excursion career for 5021 was being arranged by the Santa Fe, but the plans were dropped.
5021 sat in Southern Pacific's San Bernardino yard until 1975, when it was moved to the Southern Pacific Taylor Yard in Glendale, CA. Shortly after, it was moved back to the RailGiants Train Museum, when the GS-4 class 4449 was on display with the American Freedom Train in the Los Angeles County Fairgrounds. As of 2023, 5021 is on permanent display at the Fairplex railway exhibit in Pomona, California.