You can actually if you have energy trading between regions. The problem with California is that during peak-power use times (18:00->20:00) there is no where to buy more solar from. But California can sell its solar for other regions peak-power use time.

I think the problem is that the US grid is also not well set up for this to be viable though, but I don't know the specifics (I think the east coast is on a different grid from the west coast, and Texas has its own grid?)

Washington, Oregon, and Idaho all have lots of hydro with OR/ID good amounts of wind. CA should definitely get the transmission up to par to supply all their solar during the daytime and receive hydro+wind at night.

Love this grid map for stats on transmission: https://app.electricitymaps.com/zone/US-CAL-CISO