The average price paid for a KWh is very different than what a median customer pays for a marginal KWh. There are myriad small utilities that drag down the average price paid for a KWh in CA, but the three big IOUs cover the majority of accounts. And they all use the same transmission network.
I'm not sure how the US average residential retail number is weighted, but let's take it at face value at $0.1619/KWh. [1]
Baseline allocations are very small (around San Francisco--territory T--you get 177 KWh/mo in the summer and 234 KWh/mo in the winter). Marginal consumption is almost guaranteed to be in the second tier. Under the old default E-1 plan, that means your marginal rate is currently $0.5257/KWh. [2] This is in excess of 3x the national retail average.
But E-1 isn't the default plan any more. These days that's TOU-C. It's more difficult to come up with clean comparisons with a time-of-use plan. To keep it simple, I'll just average the rates together. The variation across time and season is not huge, so it should be good-enough approximation. Under that plan your marginal rate is around $0.5388/KWh. [3] This is also in excess of 3x the national retail average.
What about at the other end of the state? I don't know as much about baselines around San Diego since I don't live there. If we use the same assumptions for SDG&E as we did for PG&E, the marginal KWh there comes out to $0.4833/KWh. [4] This is almost exactly 3x the national average retail rate.
And if you're somewhere between these two utilities and on SCE? The same assumptions put you at $0.43/KWh. [5] So you're just barely under 3x the national average.
Considering the geographic size of the electricity grid in CA, that's not surprising. A bigger grid is more expensive to build and maintain.