As you say, dams are a net positive, and while failures do happen, these days we tend to be wiser about where we put PHES in particular.

I guess I’m surprised it isn’t more of an option for California - the U.K. uses Snowdonia as a giant battery, and afaik there’s been one failure of a dam that wiped half of trefriw off the map a century ago - which wasn’t hard as it’s a speck of a place. Since then the lakes have pretty reliably and safely provided somewhere to stick excess energy, and now are largely pumped by the offshore wind arrays nearby.

California has big mountains, but I’m not sure if the geology or terrain is right for PHES.