The Metropolitan Water District just opened a new one with an absolutely huge reservoir (though not the largest reservoir they have). It's now over half full, but they slowed down the pumping during the recent crisis so others could use the power. Now they're probably buying some of that cheap power the state is selling and running the pumps on it. It'll have a pretty good generating capacity when full.

When the MWD was excavating for the dams, they had a lot of archeaoligists and paleontologists on site, and unearthed several Indian sites and found a whole slew of totally complete mastadon skeletons, plus some mammoth skeletons (mammoths were not previously known to be this far south).

There are also a bunch of smaller pump/generator sites, some of which reverse daily with the power peaks and valleys.

We are also ramping up power generation from landfills, with a whole slew of microturbines running off the methane from rotting garbage. Later perhaps we'll mine the suckers since the largest volume is wood and paper, but right now it's cheaper to bury it (besides, landfills fight global warming by taking all that carbon out of circulation).