It usually makes more sense to pump water to a nearby reservoir uphill. That water can be released back through turbines when solar production is lower - pumped hydro are basically giant batteries. So not so much pumping it back upstream, but a similar idea, just without expensive desalination.
Not a saltwater coast, but the Ludington plant on Lake Michigan is a good example of this: https://en.wikipedia.org/wiki/Ludington_Pumped_Storage_Power_Plant
IIRC, California overproduces electricity during sunny summer days due to solar, but solar production drops in the evenings right when demand is peaking due to people getting home from work and cooking dinner and whatnot. There are better applications for that energy than desalination though - battery storage right now, and maybe running electrolyzers for green hydrogen production someday in the future.