The Horse Mesa Dam was completed in 1927, the second of three dams along the lower Salt River, between Theodore Roosevelt Lake and Phoenix, and one of two that have powerhouses with reversible turbines enabling pumped storage functions. The Horse Mesa hydroelectric plant has three conventional turbines, producing 32 megawatts. A reversible fourth unit was installed in 1972, adding another 97 megawatts to the plant’s generating capacity, and enabling the plant to pump water backwards through the system.