Putting the solar cells in the desert makes a lot of sense, but I don't understand why the pumped storage facility has to also be there. Put it somewhere else i

Putting the solar cells in the desert makes a lot of sense, but I don't understand why the pumped storage facility has to also be there. Put it somewhere else in California where there is ample water, the ground isn't as porous, and there will be less evaporation. For example, why not use something like San Luis Reservoir and the O'Neil Forebay?