The Southern Transmission System (STS) consists of a 488-mile 500 kV transmission line and the associated converter stations on each end that provides for the transmission of energy between Southern California and Rocky Mountain regional markets. When the line was originally built in 1986, the rating was for 1,920 MW. After upgrades to two AC/DC converter station in 2011, the rating increased to 2,400 MW.
SCPPA participants entered into the Southern Transmission System to bring power from one of their original projects, Intermountain Power Project, which they now longer participate in. Currently, these lines bring energy from the Milford Wind Projects in Utah.