Bottom line: pumped storage for power is a proven method for electricity "storage" and widely used. California at least has many more than one and has other projects for more. Eagle Mtn would add to the collection, which is useful not only for absorbing nuclear/coal base load at night for daytime peaking recovery, but also daytime solar or anytime wind overproduction for later use. The only real question with Eagle Mtn is where the water (the "working fluid") will come from - and the Colorado River Aqueduct is close enough that MWD's involvement should be a no-brainer.