The Middle Fork Project ( detailed in the next section ) was constructed by the Placer County Water Agency for water supply and hydropower generation , after receiving approval from the Federal Power Commission in 1963 . L.L. Anderson ( French Meadows ) Dam , completed in December 1964 , was the first major structure to be built . Hell Hole Dam on the Rubicon River was still under construction at that time when massive flooding struck northern California . More than of rain fell within five days . On December 23 the incomplete dam was overtopped and destroyed , and a wall of water swept down the Rubicon , lower Middle Fork , and lower North Fork canyons , triggering landslides , uprooting trees , and obliterating any buildings and bridges along its path . However , since there were no permanent residences in the canyon , there was no loss of human life , and the floodwaters were contained by Folsom Lake , sparing the city of Sacramento from damage . The flood surge of may have exceeded in magnitude any natural flood since the Pleistocene . The dam was rebuilt and completed in 1966
massive flooding struck northern California
Christmas flood of 1964
Middle Fork American River