The company's first proposal was to construct a rockfill diversion dam that would send water into a 20-mile (32 km)-long tunnel, developing a hydraulic head of over 1,700 feet (520 m) to supply a 120,000 hp powerhouse.

Work progressed fairly quickly, although the builders ran into problems with exfoliation of granite sheets, probably caused by drilling and explosive charges along the steep walls of the gorge.

It is an important component of Southern California Edison's Big Creek Hydroelectric Project, which comprises a system of 25 dams, nine power plants and supporting tunnels and diversion channels in the upper basin of the San Joaquin River.

Water from the reservoir is diverted into a 7.45-mile (11.99 km)-long reinforced concrete penstock into Mammoth Pool Powerhouse, which has two 100,000 hp turbines totaling a nominal generating capacity of 190 megawatts (MW).

Any higher water will flow over an uncontrolled ogee crest spillway cut into the rock of the San Joaquin Canyon about a quarter of a mile to the west of the main dam.

[10] During late summer and autumns of most years, nearly the entire flow of the San Joaquin River is diverted into the Mammoth Pool penstock, essentially drying up nearly 9 miles (14 km) of riverbed.