Located about a mile and a half upstream of the town of La Grange on the Tuolumne River, the La Grange Diversion Dam is among the oldest dams still operating in California. When it was completed in 1893 it was the highest overflow dam in the United States, built at a cost of $550,000.
Once released from Don Pedro, water flows through a steep canyon to the La Grange Diversion Dam. Once there, it can flow three different ways. It can flow into either the MID or Turlock Irrigation District’s (TID) tunnels – the head of each District’s canal system – or into the Tuolumne River. On occasions where water is abundant, it flows over the top of the dam and directly into the River.
Unlike most dams, very little water is stored behind La Grange Diversion Dam. Instead, its purpose is to raise the level of the Tuolumne River so that water can be diverted into MID and TID’s canal systems. Water flows downhill in these canals to farmers throughout MID and TID, making it possible for them to grow food for people across the nation.
In 1923, an 18-inch concrete cap was added and in 1930 an additional 24-inch cap was added, making the height 131 feet.
In 1924, TID constructed the La Grange Powerhouse which is capable of generating five megawatts of clean, carbon-free power. MID and TID are currently in the multi-year Federal Energy Regulatory Commission process for licensing La Grange Diversion Dam.