I’d agree with that. But GP’s point still stands if you specify the Midwest rather than California. In fact, that happened during the Great Depression, exacerbating hunger problems just as unemployment was peaking: a severe years-long drought in the Midwest (whence the term “dust bowl”) crippled the country’s grain production.
I doubt that the US is that dependent on California. For lettuce and strawberries, yes. Not for wheat, corn, soybeans, or cattle, though. We won't starve without salads or strawberries.
I know that I'm missing some of what California grows. Losing it would hurt. But it's not vital.