The sticking point is political, not technical or logistical. If there are ever politicians convinced climate heating, and sustainability is important, it's fixable with no more difficulty than building a highway network. Undoubtedly you'll say citizens won't tolerate the taxes that would be needed -- still a political issue. Those can change.
As the International Energy Agency noted today whilst criticising the completely inadequate efforts the globe is making: “We will need to see great political will around the world. This is why I believe that the world needs to build a grand coalition encompassing governments, investors, companies and everyone else who is genuinely committed to tackling climate change.”
> That wouldn't even cover the electricity imported into CA
In a year. CA doesn't need a year's storage backup capacity, just enough to cover cyclic shortfalls. A few hours to cover winter nights, that's under a day's worth at most.
> A smart grid allows demand and load to be managed
Which we don't have on a national (let alone international) scale, and won't have in any reasonable period of time.
> Pumped hydro can add TWh of storage if built at scale.
It's not, and it's not being built or even planned.
> sell and buy electric from surrounding countries
We can't. There's not enough transmission capacity, and there's no sign that capacity between countries is being built. We can't even ship power from the east coast to the mid-west interior.
> It is very unlikely the whole of the US will completely lack wind at the same time, especially offshore.
Which doesn't help the interior of the US - see comment about a complete lack of transmission capacity. We also have effectively-zero offshore wind capacity, and none in the works to be built.
It's a dirty secret but the US simply doesn't have the capacity to ship power any major distance. The country is broken into individual sub-groups that are maybe a thousand miles on a side that are physically incapable of linking up due to a lack of infrastructure for lots of power.
Theoretical technology won't solve our problems; Pumped Hydro is a great example. It effectively doesn't exist outside of a few demos; per Wikipedia the total installed pumped hydro storage in under 200 GWh. That wouldn't even cover the electricity imported into CA.