It's also not too dissimilar from Texas, Arizona, Oregon, Nevada, and Utah - which together are a much larger part of the US - and not too far from being able to ship power not too expensively to even more areas.
Florida and Colorado are not much farther below California in total solar radiation per year per sq meter, either.
Texas consumes almost 2x as much electricity as California [1], and is almost 1/8th the entire US consumption, so population is not the most important factor.
It also represents 12% of the country's population, which makes it a better benchmark than just being 1 of 50 states.