Yosemite

“The Yosemite Hydroelectric Power Plant and associated structures (including the diversion dam) were constructed during 1917-1918 to provide electrical power to Yosemite Valley. Water was diverted from the Merced River into a wooden penstock that paralleled El Portal Road and dropped into the power plant, where electricity was generated. The electricity was then conducted along 11-kilovolt overhead power lines from the power plant to Yosemite Valley. This complex is listed in the National Register of Historic Places, significant for engineering. Five residences were constructed in the Cascades area to provide housing for individuals responsible for maintaining and operating this system. This hydropower system is no longer in use, and many elements of it (including the dam and five houses) have been removed in consultation with the State Historic Preservation Officer and Advisory Council on Historic Preservation (NPS 1986).

…

The National Park Service purchases power from Pacific Gas & Electric Company (PG&E). Electricity is carried into Yosemite Valley via a 70,000-volt transmission line that runs overhead through El Portal and the Merced River gorge to the substation at the old Cascades Powerhouse. The powerhouse is no longer active as a hydroelectric generator but is still used as a substation. From the powerhouse, power is stepped down to 12,000 volts. Conductors extend beneath El Portal Road to a substation in Yosemite Village. The Wawona Tunnel and Big Oak Flat Tunnel are served by overhead lines from the powerhouse. The primary electric distribution system is in generally good condition after upgrades over the last 12 years, although areas in Yosemite Valley still require rehabilitation. End users in Wawona, El Portal, Foresta, and Hodgdon Meadow are served directly by PG&E, whose facilities are within the park in several places.” (Text from the Final Revised Merced River Plan/SEIS)

The Cascade Diversion Dam, built in 1979 to divert the main stem of the Merced River into the Yosemite Hydroelectric Power Plant (also known as the Cascades Powerhouse), was removed in 2003. The facilities were taken offline in the mid-1980s as the dam deteriorated and the hydropower system became outdated. The already-deteriorated dam suffered significant damage during a 1997 flood, leading to its removal 6 years later.

Read more in this report on removing historic dams (p.36).