Construction on the Cabinet Gorge Dam began in 1951 by the Morrison Knudsen Corporation. The Clark Fork River had to be diverted with two coffer dams and speed was necessary because Spring flooding threatened the river diversion and coffer dam integrity. 32 tons of dynamite was used to blast 50,000 cubic yards of rock from the canyon walls in order to prep the construction site. Water was diverted through two . tunnels and a half-million cubic yards of earth was excavated from the site overall. Construction on the dam was complete in 1952 and the reservoir was filled in 1951, half the estimated time.