An updating of P-3302 and Congressional testimony by the authors against the Grand Canyon dam projects. Calculation methods have been changed to credit the proposed alternative nuclear power plants with the Federal Power Commission's regular energy value adjustment: half the savings from replacing more expensive steam-generated peakload power. Also, cost-benefit ratios are given at both 3-1/8 (Bureau of Reclamation figure) and 5 percent interest rates. Nuclear plant costs were deliberately overstated for unassailability--if the paper were intended to evaluate current nuclear power economics for private utilities, the authors would endorse figures at least $10 per kilowatt lower. Nevertheless, this analysis finds the benefit/cost ratios of the dams to be 0.52-0.78 to one compared with the nuclear alternatives. The higher the interest rate, the greater the difference, because the dams are more capital intensive. (See also P-3505, P-3541, P-3548.) 18 pp. Ref.