The SPSR commenced operations in November 2003 after David Parkinson acquired the San Pedro and Southwestern Railway (reporting mark SWKR) from RailAmerica in 2003 with "the intent of restoring transborder rail service with the Mexican rail system at Naco, Arizona, and developing North American Free Trade Agreement-related traffic, but that this plan never materialized."

David Parkinson had owned several other shortlines in the western US, such as the California Northern Railroad, under his ParkSierra Rail Group, which was sold in 2002 to RailAmerica, which was purchased in turn by Genesee & Wyoming in 2012.

SWKR decided to abandon the line south of Curtiss in March 2005 due to limited freight business and the lack of prospects for future traffic increases.

In 1888 Arizona & Southeastern built a 60-mile (97 km) line southward along the San Pedro River from a connection with the Southern Pacific Railroad at Benson to Bisbee.

The A&SE track partially paralleled the New Mexico and Arizona Railroad (NM&A) that was built six years earlier (1882) on the opposite side of the San Pedro River from Benson to Fairbank.

The STB ruled that the Offer of Financial Assistance (OFA) deal of the agreed upon price of $5.6 million for the SPROC railroad line from Curtiss to Naco and Paul Spur must close on or before July 12, 2006.

In October 2018, the line was sold by ARG Transportation Services to Ironhorse Resources and renamed the San Pedro Valley Railroad.