[PaulDavisThe1st]

This is not quite true. Most western US (well, say CA central valley back to the plains) agriculture has been made possible by large scale irrigation systems backed by the construction of substantial reservoirs. From time to time, it has been necessary to pull from groundwater, and from time to time, some farmers have done so even when it wasn't necessary. But in general, most of the agricultural expansion has been based on collected rainwater, distributed via huge systems. This system has worked "well" as long as the snow and the rain has kept coming (and flowing, rather than being absorbed into warm-weather baked soil). But the rain & snow are not making it into the rivers and reservoirs, and so this system has serious problems now.

By contrast, plains and some midwestern ag. has been drawing down the Ogallala aquifer at an insane rate, and that really is "fossil water".

[dreamcompiler]

Correct. I overgeneralized; the coastal western states might be able to continue some farming. Assuming cities like LA don't continue to appropriate more and more water that fell to the ground hundreds of miles away.