California uses more pumped storage than is generally realized. Some of the reservoirs of the California Water Project are uphill from their water source, and thus have large pumps. These can also be run as generators. They pump water uphill at night when power is cheap, and generate power during the daytime peak. This generates some profit for the CWP. The reservoirs and pumps are needed anyway, so there's very little capital cost associated with doing this. Because big Water Project storage reservoirs are involved, the water levels don't change rapidly.

Purpose-built pumped storage plants, such as Helms near Fresno, tend to have much smaller reservoirs, about enough for a daily cycle, and they go from full to empty and back each day. This annoys some people. They're not recreational lakes. Efficiency is 60% - 80% round trip from electricity in to electricity out.