There is a proposal to convert the Hoover Damn and Lake Mead into pumped storage.

https://www.utilitydive.com/news/los-angeles-considers-3b-pu...

https://www.nytimes.com/interactive/2018/07/24/business/ener...

I thought they were already used as pumped storage? I know the grand coullee has the ability to pump water up into its reaovoir, at least they talked about this in a high school class I took 25 years ago.

THey can build transmission lines into WA and OR and get hydrop from there.

A ton of pacific northwest hydropower is already flowing into California through the BPA's intertie system:

https://www.bpa.gov/news/pubs/FactSheets/fs-20170726-BPA-set...

Assuming those states want to sell power to CA. I suppose they would if CA is willing to pay for it.