About 15,000 years ago, Lake Bonneville, the larger ancestor of Salt Lake, flooded this area and carved Twin Falls, named for the pair of cataracts that once poured over these rocks. In 1935, Idaho Power began construction on the original dams and power plant; because there was no road into the site, crews used an electrically powered skip that traveled on a well-greased, 260-foot wooden ramp to move equipment and supplies into and out of the canyon. The arch dam, 789 feet long, was built in 1935 along with the non-overflow dam and powerhouse. The 1935 power plant generates 9 megawatts, is used when water flows are 100 to 1,000 cubic feet per second, was built in one year, and uses a Francis turbine. In 1995, a new power plant was built on the floor of the Snake River below Twin Falls, where large cranes were used and a generator rotor was lowered into place; when water turns the turbine, it also turns the rotor, whose magnetic field creates electricity. The 1995 power plant generates 43.5 megawatts, is used when water flows are 1,000 to 4,000 cubic feet per second, was built in two years, and uses a Kaplan turbine with blades that change pitch for efficiency at varied flows; both plants are used at the same time for flows above 4,000 cubic feet per second. Twin Falls Reservoir is also a place for boating, swimming, fishing, picnicking, and enjoying the canyon, and the two power plants together can generate enough electricity for approximately 31,900 homes.